AC Mode Switch - Electrical?

[Kozmatic]

Hi! Just brought 3849 home today here in Florida. She runs great and would love to be out driving her today but alas the AC is not working.

So I'm not getting it to do anything - no blower coming on at any speed and no compressor kicking in. I swapped a circuit breaker - nothing..still no blower.

Pulled console to checkout mode switch - seems to be in good shape. With motor running, I can switch modes and see the vents in the center opening and closing. No Hiss when running.

I was thinking switch because neither the blower or compressor turns on.

Now, it was just charged/serviced before it was shipped to me from Illinois...this past Tuesday. Seller is indicating that blower was working and thinks it could have been something knocked loose when AC was charged.

I'm trying to figure out what to check next before I put the console back together. Any ideas?

[Josh]

When you click to speed 3 and 4 you should hear the relays engaging. If not, I would check fuse #10 which supplies power to the switch.

[Kozmatic]

Fuse is good....door lock light is on and pulling it cuts the light out. so power to the switch then, right? Should I be able to measure voltage at the connections on the switch then?

[Kozmatic]

i forgot to mention that I measured no voltage at the blower connection under the dash. so it's not getting there it seems.

[Josh]

Ok that clears up the power to the switch. Like i said relays on 3 and 4, so not 1 and 2. So even if the relays arent engaging theoretically speeds 1 and 2 should.

From here I would probe the light green wire on the back of the mode switch. If its not giving out 12v when anywhere other than off the switch is to blame.
Another test to confirm this is to hook 12v (fused for 20a) to the light green wire going into the fan speed switch. If the fan starts spinning in all speeds the mode switch is once again to blame.
Edit, just jump the light green and white wire with the light green from the back of the mode switch.

[Kozmatic]

Power at all connections at mode switch. so that's good. confusing

[Josh]

if there is power at all the terminals the compressor clutch should be kicking in.

maybe its the fan speed switch that is hooped? probe the connections at the back of the switch (remember light green is incoming, all the striped black wires are designated to a speed) and see if they are putting out 12v.

[Kozmatic]

(remember light green is incoming, all the striped black wires are designated to a speed) and see if they are putting out 12v.

That's good to know....thank you....checking there next

[Kozmatic]

if there is power at all the terminals the compressor clutch should be kicking in.

maybe its the fan speed switch that is hooped? probe the connections at the back of the switch (remember light green is incoming, all the striped black wires are designated to a speed) and see if they are putting out 12v.

Ok, so no power at the fan speed select switch. I'm trying to work my way back. Would this go back to the breaker 18? If so, no power there either. Not sure where to go. Relay perhaps?

Thanks for your help!

[Kozmatic]

Ok, so no power at the fan speed select switch. I'm trying to work my way back. Would this go back to the breaker 18? If so, no power there either. Not sure where to go. Relay perhaps?

Thanks for your help!

Correction. Realized the mode switch had to be on for there to be power at the fan speed switch. There's power. Speed switch is bad. Not sure if that has anything to do with the compressor or not, but certainly fan speed.

[Rich]

So I'm not getting it to do anything - no blower coming on at any speed and no compressor kicking in.

I was thinking switch because neither the blower or compressor turns on.

Now, it was just charged/serviced before it was shipped to me from Illinois...this past Tuesday. Seller is indicating that blower was working and thinks it could have been something knocked loose when AC was charged.

It is possible that the blower failure and the compressor failure are unrelated.

A normal refrigerant recharge would not knock anything loose. If they botched the recharge and somehow you are low on refrigerant then the compressor will not kick in because the low-press switch isn't closed.

And be sure to check the diagram, shown at top of first post here: http://dmctalk.org/showthread.php?40-All-Wiring-Schematics

As for your fan speed switch be sure it isn't just wiring or connector corrosion before you replace it. Run a continuity check. If you lost all speeds then the input contact or the feed wiring are suspect.

[Kozmatic]

It is possible that the blower failure and the compressor failure are unrelated.

A normal refrigerant recharge would not knock anything loose. If they botched the recharge and somehow you are low on refrigerant then the compressor will not kick in because the low-press switch isn't closed.

And be sure to check the diagram, shown at top of first post here: http://dmctalk.org/showthread.php?40-All-Wiring-Schematics

As for your fan speed switch be sure it isn't just wiring or connector corrosion before you replace it. Run a continuity check. If you lost all speeds then the input contact or the feed wiring are suspect.

Was able to repair the switch....didn't realize but as I disconnected the plug from it, it pulled the back of it off. I was able to figure out the orientation and snap it back in place. It is working normally now with all four speeds. Now just down to the compressor.

Thank you all for your help! I'll take these baby steps

[DMC5180]

Compressor not engaging is most likely LOW refrigerant charge. You can confirm this by removing the connector from the Low pressure switch (the switch it located on the side of the A/C accumulator behind the right front wheel). Pull the connector from the switch and make a short jumper and plug that into the connector. Turn the KEY to the run Position > Switch the mode switch to A/C> You should hear A/C clutch Snap and Radiator Fans come ON> If yes, the circuit is confirmed good and your charge is LOW (or you have a Bad LP switch, not likely though) IF, the clutch does NOT snap, you will need to look at wire connections in the Relay compartment (confirm you don't have an open Diode) and or good connection at the BH connector.

[Kozmatic]

Compressor not engaging is most likely LOW refrigerant charge. You can confirm this by removing the connector from the Low pressure switch (the switch it located on the side of the A/C accumulator behind the right front wheel). Pull the connector from the switch and make a short jumper and plug that into the connector. Turn the KEY to the run Position > Switch the mode switch to A/C> You should hear A/C clutch Snap and Radiator Fans come ON> If yes, the circuit is confirmed good and your charge is LOW (or you have a Bad LP switch, not likely though) IF, the clutch does NOT snap, you will need to look at wire connections in the Relay compartment (confirm you don't have an open Diode) and or good connection at the BH connector.

Thanks! I did the LPS jumper and fans and compressor kicked on. I started the car and boom - cold air!

Guess I have a bad LPS? I'm assuming you cannot just pul it out without losing freon? I thought I read somewhere that there's an adjustment for the pressure at the switch but I don't see anything like that.

[Jonathan]

Thanks! I did the LPS jumper and fans and compressor kicked on. I started the car and boom - cold air!

Guess I have a bad LPS? I'm assuming you cannot just pul it out without losing freon? I thought I read somewhere that there's an adjustment for the pressure at the switch but I don't see anything like that.

Two things:

1.) Cold air probably is saying there is Freon in the system, but you would not normally want to go driving around with that jumper in place. If the Freon is low or becomes low and your car can't shut the system off when it needs to, there are some components that could be damaged fairly quickly. This would be an expensive lesson for you unfortunately.

2.) You might get lucky and it could be the connector on your LPS was just not making good contact because of the aforementioned corrosion possibility. Give 'er the ole plug it in, unplug it, plug it in, unplug it, sure-fire-remove-that-corrosion-special-Lotus-engineering-don't-fail-me-now solution and you might not have to replace anything.

Hopefully that works.

[DMCMW Dave]

Thanks! I did the LPS jumper and fans and compressor kicked on. I started the car and boom - cold air!

Guess I have a bad LPS? I'm assuming you cannot just pul it out without losing freon? I thought I read somewhere that there's an adjustment for the pressure at the switch but I don't see anything like that.

There is a achrader valve behind the switch. They sometimes stick so work fast. Don't leave the lp switch jumped. I've seen people destroy compressors that way.


Sent from phone

[Kozmatic]

Tried the remove and reattach the connector several times....no luck. Found the adjustment screw. Turned it in each direction up to one full turn and tested....still nothing. Not sure that's even a valid test.

[DMC5180]

Tried the remove and reattach the connector several times....no luck. Found the adjustment screw. Turned it in each direction up to one full turn and tested....still nothing. Not sure that's even a valid test.

Just reading back up the thread and I don't see where it says the system had been serviced or confirmed working before you brought the car home. The jumper TEST made the system run, but that does not mean the system has adequate charge. "Boom Blows Cold" (how cold?) Or do you think it blows cold just because is BLOWS (fan runs)

Also +1 on what Dave said. Do Not run the system beyond what is necessary to diagnose it with the jumper installed.

[Kozmatic]

Just reading back up the thread and I don't see where it says the system had been serviced or confirmed working before you brought the car home. The jumper TEST made the system run, but that does not mean the system has adequate charge. "Boom Blows Cold" (how cold?) Or do you think it blows cold just because is BLOWS (fan runs)

Also +1 on what Dave said. Do Not run the system beyond what is necessary to diagnose it with the jumper installed.

Gotcha...here's the story. Seller supposedly has the AC serviced right before delivery to me via a Chevy dealer. He said it blew cool, not cold. In hindsight I think maybe the compressor wasn't kicking it at all. Totally possible that it never really went to that dealer and nothing has been done....I have no proof.

As for my impression that it's cold, it certainly is cold. Clearly much colder than just the fans running. You can also feel the accumulator getting cold as well.

Certainly will not drive it with a jumper, but just trying to diagnose. There's obviously some freon in the system or it would not get cool at all. I guess the question is how much. There has been a r134 conversion done on the fittings which the seller did tell me and I can visually confirm.

I'm trying to diag as far as I can as taking it to a shop around here is questionable....but I can ask another owner in the area if needed.

Here's my question - should adjusting the switch make any difference at this point in troubleshooting, with the idea of figuring out if the switch is bad? In other words, should I be able to adjust it to the point that it closes just to see if it's working? Asking because I tried going up to two or three full turns in both directions with no changes.

[DMCMW Dave]

If the system is empty it will never come on. The adjuster on the switch is also the major leak point. So you'll need to replace the switch anyway. Have you put gauges on it? If not you are flying blind. Are the r134 fitting quality steel fitting at the aluminum junk?


Sent from phone

[Kozmatic]

If the system is empty it will never come on. The adjuster on the switch is also the major leak point. So you'll need to replace the switch anyway. Have you put gauges on it? If not you are flying blind. Are the r134 fitting quality steel fitting at the aluminum junk?


Sent from phone

I spoke too soon I guess. The switch is working now, although it's not cycling. Just running...blowing real cold. I'll get some gauges on it.


Thank you all

[NightFlyer]

If your service ports (on the high and low hoses connectors where they join with the compressor) are stock/OEM with no adapters of any kind on them, then you can use a pressure gauge with a female 1/4" SAE tapered fitting (must have a build in schrader core depressor to work), on either the high or low side port to determine how much of a charge is currently in your system.

Do this with the car off and a cold engine. You must also know the ambient temperature of the air around the car.

Then, based upon what kind of refrigerant you have in the system, reference the static temperature/pressure charts for that kind of refrigerant.

For example, at 76F (24.4C) ambient air temperature, the static pressure representing a full charge of the system are as follows (in pounds per square inch):

Refrigerant : Pressure
R-12 : 78.2
R-22 : 134.5
R-134a : 80.2
R-152a : 71

If the pressure your reading is lower than the pressure required for a full charge, then you know that your system is undercharged. Not sure how how undercharged it needs to be to prevent the compressor from activating, but at least you'll know if you need to add refrigerant to the system.

If this is the first time you've attempted to run the A/C on the car in several years, then you may want to evacuate/depressurize the system, change out the schrader cores in the service ports, pull the compressor, drain it of oil, replace the o-rings at the hose connections, back flush the system with appropriate solvent (mineral spirits or lacquer thinner), blow it out both ways with compressed air until most of the solvent used is out of the system, add new oil to the compressor (6oz-8oz of mineral if your keeping R-12, ester if you'll be running a 12a product, R-22, R-134a, or R-152a), reconnect the compressor, vacuum down the system for a good period of time to pull out any air and boil out any moisture, and then recharge with the refrigerant of your choice.

[Jonathan]

I spoke too soon I guess. The switch is working now, although it's not cycling. Just running...blowing real cold. I'll get some gauges on it.


Thank you all

Just to also mention, you can test to see whether the compressor will come on without actually running the engine. If you are/were at the stage where you wanted to test the LPS or the electrical points in between, you can turn the key in the ignition (without starting the engine) and if you have the mode selector on A/C or MAX and the temperature knob clicked all the way around, you will be able to hear the compressor clutch "clack" in. This is a good test to see how much is working before you get to the part about how much Freon is in the system and run (no pun intended) the risk of damaging something.

[NightFlyer]

I was typing out my previous post before you posted the details about the condition of your system.

So you have an R-134a conversion. Here's a link to the temperature/pressure chart direct from the source of the patent holder:

http://www2.dupont.com/Refrigerants/en_US/assets/downloads/k10909_Suva_pressure_temp_eng.pdf

Sounds like the system had some work done to it. Assuming it was done correctly, all you should have to do is assure the proper amount of refrigerant in the system, and get the LPS figured out so that the compressor activates and cycles correctly (as you are already aware).

Best luck :thumbup:

[Kozmatic]

I was typing out my previous post before you posted the details about the condition of your system.

So you have an R-134a conversion. Here's a link to the temperature/pressure chart direct from the source of the patent holder:

http://www2.dupont.com/Refrigerants/en_US/assets/downloads/k10909_Suva_pressure_temp_eng.pdf

Sounds like the system had some work done to it. Assuming it was done correctly, all you should have to do is assure the proper amount of refrigerant in the system, and get the LPS figured out so that the compressor activates and cycles correctly (as you are already aware).

Best luck :thumbup:

Thanks! Seems like I'm getting close.... and boy do I need it. 90 plus with 90 % humidity is NO JOKE right now, lol. Clearly some work as you indicated has been done. My adjustment to the LPS seems to have worked as to get the compressor to turn on, but it does not appear to be cycling, but man it blows cold! I'm stuck until I get a gauge on it. I have some el-cheap-o gauges from Harbor Freight I've never actually used. Onward march!

For reference here's a pic of the connections. Looks like they may be the cheap ones. :question:

Thank all you guys for your help! I love this community! :thankyou:

29403

[DMC5180]

I spoke too soon I guess. The switch is working now, although it's not cycling. Just running...blowing real cold. I'll get some gauges on it.


Thank you all

You definitely need to put gauges on it. The cycling pressures for 134a should be ON @ 45 PSI OFF @ 26-28 PSI. I believe the upper 45 PSI is a fixed setting. The Lower 26-28 is range adjustable. The switch was probably still at factory setting of 30 PSI for R12 You do not want the compressor to run below these setting or the Evaporator could/will freeze up.

[Jonathan]

If the compressor is not cycling off, could there be a problem with your high pressure cut-off switch? (albeit I don't know where that one is off the top of my head but assume it's somewhere in the vicinity.)

[DMC5180]

Just to also mention, you can test to see whether the compressor will come on without actually running the engine. If you are/were at the stage where you wanted to test the LPS or the electrical points in between, you can turn the key in the ignition (without starting the engine) and if you have the mode selector on A/C or MAX and the temperature knob clicked all the way around, you will be able to hear the compressor clutch "clack" in. This is a good test to see how much is working before you get to the part about how much Freon is in the system and run (no pun intended) the risk of damaging something.


Covered this previously in post #13 :biggrin:

[DMC5180]

If the compressor is not cycling off, could there be a problem with your high pressure cut-off switch? (albeit I don't know where that one is off the top of my head but assume it's somewhere in the vicinity.)

High pressure cut-off is a safety switch BEFORE the Evaporator in the event the orifice tube becomes plugged and would require very high pressure to turn the system OFF. This switch remains CLOSED in all but the most extreme case.

On-Off cycling is function of the LP switch. The LP and HP switches are wired in series too.

[Kozmatic]

Ok so I have gauges on it. Low side pressure drops and drops and compressor doesn't shut off. I've from one extreme to the other. I found a online video that shows counter clockwise turns to adjust to get it to cut off at higher pressure.

So far I'm not getting anywhere with that. The adjustment screw thread are showing now. Here's the question - can't the adjustment take a few minute before the switch would notice? Seems like that may have happened before to get it working in the first place. In other word, should I wait a certain a mount of time after turning the screw before testing?

[NightFlyer]

Ok so I have gauges on it. Low side pressure drops and drops and compressor doesn't shut off. I've from one extreme to the other. I found a online video that shows counter clockwise turns to adjust to get it to cut off at higher pressure.

So far I'm not getting anywhere with that. The adjustment screw thread are showing now. Here's the question - can't the adjustment take a few minute before the switch would notice? Seems like that may have happened before to get it working in the first place. In other word, should I wait a certain a mount of time after turning the screw before testing?

I'm pretty sure that turning the adjustment screw clockwise has the effect of getting the compressor to cut-off at higher low-side pressures, while turning it counter-clockwise has the effect of getting the compressor to cut-off at lower low side pressures.

Try turning it clockwise to raise the low-side pressure at which the compressor will kick off at.

[Rich]

Ok so I have gauges on it. Low side pressure drops and drops and compressor doesn't shut off....

Not sure what drops and drops means.

Can you report what the the gauge data is? Both high side and low side pressures.

And under what conditions (engine speed, outside temperature)?

You report that the A/C compressor does not cycle. Depending on the engine speed, temperature and refrigerant charge the compressor may not need to cycle.

[DMC5180]

Ok so I have gauges on it. Low side pressure drops and drops and compressor doesn't shut off. I've from one extreme to the other. I found a online video that shows counter clockwise turns to adjust to get it to cut off at higher pressure.

So far I'm not getting anywhere with that. The adjustment screw thread are showing now. Here's the question - can't the adjustment take a few minute before the switch would notice? Seems like that may have happened before to get it working in the first place. In other word, should I wait a certain a mount of time after turning the screw before testing?


I don't believe there is a delay in making the adjustments. Turn the screw back to about where it was when you started the process. Also If it is as hot as you say the system probably won't cycle OFF at idle. Raise the engine RPM and see what difference that makes. Turn too MAX A/C w/ FAN on 4

[NightFlyer]

Yes, in high ambient temps/humidity, the compressor will constantly stay running at idle, as Dennis stated.

Raise the engine RPM and put a box fan blowing across the condenser to simulate driving conditions while the car remains stationary.

[Kozmatic]

Yes, in high ambient temps/humidity, the compressor will constantly stay running at idle, as Dennis stated.

Raise the engine RPM and put a box fan blowing across the condenser to simulate driving conditions while the car remains stationary.

Yeah I did increase rpms to about 2k but no change. I'll go back and a just the other way. .... Gotta break for a while before my family thinks I left them for a car....errrr....uh..

[DMC5180]

.... Gotta break for a while before my family thinks I left them for a car....errrr....uh..

LOL :tantrum:

[Bitsyncmaster]

If your service ports (on the high and low hoses connectors where they join with the compressor) are stock/OEM with no adapters of any kind on them, then you can use a pressure gauge with a female 1/4" SAE tapered fitting (must have a build in schrader core depressor to work), on either the high or low side port to determine how much of a charge is currently in your system.

Do this with the car off and a cold engine. You must also know the ambient temperature of the air around the car.

Then, based upon what kind of refrigerant you have in the system, reference the static temperature/pressure charts for that kind of refrigerant.

For example, at 76F (24.4C) ambient air temperature, the static pressure representing a full charge of the system are as follows (in pounds per square inch):

Refrigerant : Pressure
R-12 : 78.2
R-22 : 134.5
R-134a : 80.2
R-152a : 71

If the pressure your reading is lower than the pressure required for a full charge, then you know that your system is undercharged. Not sure how how undercharged it needs to be to prevent the compressor from activating, but at least you'll know if you need to add refrigerant to the system.

If this is the first time you've attempted to run the A/C on the car in several years, then you may want to evacuate/depressurize the system, change out the schrader cores in the service ports, pull the compressor, drain it of oil, replace the o-rings at the hose connections, back flush the system with appropriate solvent (mineral spirits or lacquer thinner), blow it out both ways with compressed air until most of the solvent used is out of the system, add new oil to the compressor (6oz-8oz of mineral if your keeping R-12, ester if you'll be running a 12a product, R-22, R-134a, or R-152a), reconnect the compressor, vacuum down the system for a good period of time to pull out any air and boil out any moisture, and then recharge with the refrigerant of your choice.

Static pressure will not tell you the amount of charge. It will just indicate if you have some liquid refrigerant in the system or not. Even one oz. of liquid will read the same pressure as 20 oz.

[NightFlyer]

Static pressure will not tell you the amount of charge. It will just indicate if you have some liquid refrigerant in the system or not. Even one oz. of liquid will read the same pressure as 20 oz.

That's what I used in doing my R-152a conversion (the second time around), which worked well enough that it was freezing the evaporator with minimal compressor cycling (had to adjust the LPS so that the compressor hardly kicks on at all) :dunno:

My initial charge was way low - I now know this.

My subsequent charge started out too high, but I vented some of the refrigerant the same way you'd vent air out of a tire when setting the pressure.

Relieving the system of an ounce of refrigerant definitely caused the static pressure that the system was reading to decrease to where I wanted it to be according to the chart based on the ambient air temperature around the system.

What good would the static pressure charts be if they didn't tell you something about the status of your system?

I honestly don't know if using static pressure to determine system charge status is right or wrong - only that setting it as you would a tire based on the ambient air temperature's corresponding pressure number as indicated on the static pressure charts worked pretty much perfectly for me.

Your mileage may vary.

[Bitsyncmaster]

Relieving the system of an ounce of refrigerant definitely caused the static pressure that the system was reading to decrease to where I wanted it to be according to the chart based on the ambient air temperature around the system.

When you vented an ounce of refrigerant the system got colder (refrigerant cools changing from liquid to vapor) and hence the drop in pressure. Now if you waited until the system got back up to the room temp you would see the same pressure you saw before you vented. I can't convince Bill of this either.:sad30:

Put your gauge on my 30 lbs tank at the same temperature and you will see the same pressure.

[NightFlyer]

When you vented an ounce of refrigerant the system got colder (refrigerant cools changing from liquid to vapor) and hence the drop in pressure. Now if you waited until the system got back up to the room temp you would see the same pressure you saw before you vented. I can't convince Bill of this either.:sad30:

Put your gauge on my 30 lbs tank at the same temperature and you will see the same pressure.

I'll put my gauge on tonight and see where the pressure is currently at :)

[Kozmatic]

Not sure what drops and drops means.

Can you report what the the gauge data is? Both high side and low side pressures.

And under what conditions (engine speed, outside temperature)?

You report that the A/C compressor does not cycle. Depending on the engine speed, temperature and refrigerant charge the compressor may not need to cycle.

Yeah I guess drops and drops was a worthless statement, lol.

Outside temp - 88-90, humidity 60 ish

So with AC off, low side was 25 and high was around 62 or so. Turn AC on, compressor on, low drops as far as 5. As I said, blows cold that whole time. I didn't leave it like that very long. After reading more, it sounds like it should be off at 25. So does this indicate low refrigerant?

As for the switch, have I screwed it up? Seems like it should not be working with the pressure that low regardless. I still have not been able to get back and try the adjustment back to where I found it yet, but that was my next test. When I do, I'll record the exact pressure readings.

[Bitsyncmaster]

I'll put my gauge on tonight and see where the pressure is currently at :)

Good plan.

You can also just put a can on your gauge, check the pressure, vent a few oz, wait a long time because that can will be freezing cold now. Then read the pressure, it should still follow the static pressure table no matter what the amount of liquid in the can. Of course when you have no liquid then it won't work

[Kozmatic]

My readings - still around 89 outside temp, 60% humidity

I'm using pics just so i have more eyes reading this. I appreciate you all taking the time with me on this. I know a lot about a lot of things - AC is clearly NOT one of them!

Static pressure - engine not running 29426

Engine idle -- 29427

Higher RPMs - 2-3k 29428

[DMC5180]

Yeah I guess drops and drops was a worthless statement, lol.

Outside temp - 88-90, humidity 60 ish

So with AC off, low side was 25 and high was around 62 or so. Turn AC on, compressor on, low drops as far as 5. As I said, blows cold that whole time. I didn't leave it like that very long. After reading more, it sounds like it should be off at 25. So does this indicate low refrigerant?

As for the switch, have I screwed it up? Seems like it should not be working with the pressure that low regardless. I still have not been able to get back and try the adjustment back to where I found it yet, but that was my next test. When I do, I'll record the exact pressure readings.

With the A/C OFF you should be seeing equal STATIC pressure on both gauges. It's a closed system. Are you sure you have the port valves open?

[Kozmatic]

With the A/C OFF you should be seeing equal pressure on both gauges. It's a closed system. Are you sure you have the port valves open?

just checked...they're open. could the gauges not be exactly right as they're within a cpl lbs.

[Bitsyncmaster]

You know the PSI scale is the inside numbers. So your getting 42 PSI low side and 190 PSI high side at idle. Your 250 PSI running higher RPM tells me your charged pretty full.

[Kozmatic]

You know the PSI scale is the inside numbers. So your getting 42 PSI low side and 190 PSI high side at idle. Your 250 PSI running higher RPM tells me your charged pretty full.

I'm the first to admit I'm not very knowledgeable here, but are you saying to read the BLACK Inside and NOT the BLack Outside that says r134a?

[Kozmatic]

You know the PSI scale is the inside numbers. So your getting 42 PSI low side and 190 PSI high side at idle. Your 250 PSI running higher RPM tells me your charged pretty full.

Also, if using those numbers - 42 PSI low and 190 PSI high, what next then? I still have not been able to get the compressor to cycle. I've tried the high RPMs, with the box fan in front of the car running for some time. I've tried different fan speeds.

I'm not sure where to go from here or if I'm ok.

[Bitsyncmaster]

I'm the first to admit I'm not very knowledgeable here, but are you saying to read the BLACK Inside and NOT the BLack Outside that says r134a?

Yes if you want to read PSI.

The other scales show temperature for that pressure (static pressure).

[Kozmatic]

Yes if you want to read PSI.

The other scales show temperature for that pressure (static pressure).

OK...I'm with you. Thanks for explaining that I cannot read a gauge correctly. LOL...I didn't take the time to think about what I was reading there.

So, what do you make of the compressor not cycling? How can I make sure the system is operating correctly? Is it possible that the pressure just never gets low enough? I'm confused on how to evaluate the current status.

[Bitsyncmaster]

OK...I'm with you. Thanks for explaining that I cannot read a gauge correctly. LOL...I didn't take the time to think about what I was reading there.

So, what do you make of the compressor not cycling? How can I make sure the system is operating correctly? Is it possible that the pressure just never gets low enough? I'm confused on how to evaluate the current status.

Run your AC with the fan speed on #1 speed and you should see it cycle. Your low pressure switch may be set to low since I saw 25 PSI on your high RPM test.

[DMC5180]

My readings - still around 89 outside temp, 60% humidity

I'm using pics just so i have more eyes reading this. I appreciate you all taking the time with me on this. I know a lot about a lot of things - AC is clearly NOT one of them!

Static pressure - engine not running 29426

Engine idle -- 29427

Higher RPMs - 2-3k 29428

Your gauges appear to OFF slightly in Calibration LOW side shows 10 PSI less than HIGH side But we will call it 110 PSI for now.

When IDLING the LO side is showing 42 PSI ( so at Idle this number stays fairly constant and only drops when increase RPM?) Fundamentally, the system will cycle ON when the pressure reaches 45 PSI the pressure should DROP from there to the point when it reaches 26-28 it cycles OFF. DEPENDING on environmental conditions. It can hoover in the RANGE between 26 and 45 and therefore never turn off.

Try this: with A/C on MAX set the fan speed at 1 and close the doors. This will usually force a rapid cycle situation. Report back on where the the LO side pressure cuts off.


AT 2K the LO side is at 25 PSI This tells me the switch pressure needs to be increased a little if it is not cutting the compressor OFF

Yeah, What DAVE said: LOL

[Kozmatic]

Run your AC with the fan speed on #1 speed and you should see it cycle. Your low pressure switch may be set to low since I saw 25 PSI on your high RPM test.

OK...should this test be at idle or higher RPM?

[Bitsyncmaster]

OK...should this test be at idle or higher RPM?

It should work at idle.

[Bitsyncmaster]

Yeah, What DAVE said: LOL

Beat you by 4 min. We think alike.

[DMC5180]

OK...should this test be at idle or higher RPM?


try it at idle if nothing happens just increase rpm it should not hurt anything (remember when your driving the RPM is somewhere between 2 and 3 K)

[NightFlyer]

So with AC off, low side was 25 and high was around 62 or so.

Not sure if this has been addressed yet or not (haven't read all the new posts yet), but static pressure with the system off should be the same on both the high and low side (assuming that a source of localized heat isn't interfering with one of the sides, which is why static pressure is best taken with the engine cold and off). If they're not the same, it's indicative of unwanted blockage somewhere in the system.

[Kozmatic]

well, doors closed, max AC on fan speed 1 - it just will not cycle. Runs the whole time. Nice and cool in the cabin though!

[Bitsyncmaster]

well, doors closed, max AC on fan speed 1 - it just will not cycle. Runs the whole time. Nice and cool in the cabin though!

How low does the low pressure get? You may have a bad low pressure switch or someone jumped it.

[Kozmatic]

How low does the low pressure get? You may have a bad low pressure switch or someone jumped it.

lowest around 25. I've adjusted the switch so it's not jumped. It cuts out along with fans when i disconnect it to adjust. I'm thinking the switch could be bad as I've adjusted it damn near as far as the screw will go in both directions trying to get it to do something different.

[NightFlyer]

My readings - still around 89 outside temp, 60% humidity

Static pressure - engine not running 29426

OK, so you have an ambient of 89F.

According to the chart, with R-134a, you want to see a pressure of about 102 psi at such a an ambient temp.

Both gauges are reading a pressure of around 102 psi, thus I'd say that you have a suitable charge of R-134a in your system, and the fact that both sides are equal suggests that the system is free/clear of any unintended blockages.

However, Dave M. has said that this not a reliable way to determine the sufficiency of a system charge, thus take my assessment with a grain of salt (even though it worked well for me)....

[DMC5180]

Here is a very good Tutorial for troubleshooting/theory of operation in a Typical Automotive A/C system: it's a very good read and will answer many questions you might have been wondering about.

http://aircondition.com/tech/questions/82/Troubleshooting-with-Gauges-FAQ

[Bitsyncmaster]

lowest around 25. I've adjusted the switch so it's not jumped. It cuts out along with fans when i disconnect it to adjust. I'm thinking the switch could be bad as I've adjusted it damn near as far as the screw will go in both directions trying to get it to do something different.

You can replace the switch without loosing much refrigerant.

[NightFlyer]

Higher RPMs - 2-3k 29428

Your low side pressure is approaching 25psi, thus proper adjustment of the switch should be causing the compressor to cycle-off. As you're not getting a response regardless of how you have the switch adjusted, then I'm thinking that you have a defective LPS, and it will need to be replaced.

Best luck :thumbup:

I'm convinced that your system does have a full charge of refrigerant in it, thus I believe you to be good to go in that respect, if that's any consolation.... :wink:

[Kozmatic]

Your low side pressure is approaching 25psi, thus proper adjustment of the switch should be causing the compressor to cycle-off. As you're not getting a response regardless of how you have the switch adjusted, then I'm thinking that you have a defective LPS, and it will need to be replaced.

Best luck :thumbup:

I'm convinced that your system does have a full charge of refrigerant in it, thus I believe you to be good to go in that respect, if that's any consolation.... :wink:

It certainly is! Thank you to everyone who's taken time to walk me through this! I'll get a new switch and go from there.

[kings1527]

There are only a couple of things (aside from some maverick rewiring) that control the compressor from cycling on/off (or just staying off):

1) low charge, which seems to be ruled out.
and
2) a defective (or improperly adjusted) low pressure switch.

The circuit is pretty simple, kind of like troubleshooting the radiator fans not coming on. Usually either the otterstat or the fan relay.

My money is on you having a bad low pressure switch. Very easy and cheap to swap out and confirm! But again, double check the low pressure switch connection. After doing some work on the system, mine was very seasonal on making good contact and I had to work on the contacts a bit.

As far as how long it takes for the system to right itself after an adjustment to the LPS, it's relatively instant. Maybe within 30 seconds or so. But any adjustment to the LPS MUST be done with gauges. There's no other way to tell. If you get the evaporator too cold, the refrigerant oil becomes too viscous and won't flow through the system properly. This in turn can damage your compressor. And turn your evaporator into an ice block.

On a side note, if you install a new LPS be sure not to forget the o-ring that goes inside it. I was chasing around a slow leak forever when I forgot to put that one in. :sad30:

[Ron]

Do this with the car off and a cold engine. You must also know the ambient temperature of the air around the car.

Then, based upon what kind of refrigerant you have in the system, reference the static temperature/pressure charts for that kind of refrigerant.

For example, at 76F (24.4C) ambient air temperature, the static pressure representing a full charge of the system are as follows (in pounds per square inch):

Refrigerant : Pressure
R-12 : 78.2
R-22 : 134.5
R-134a : 80.2
R-152a : 71
Josh,
Temperature-Pressure conversion(s) should be right on the gauge (Be careful- Many Gauges are in C not F):
29434 (Click to enlarge)
To get the correct correct charge (on a D and others) you must check the high and low side at the moment the clutch cycles out and compare to a Pressure Data Chart (NOT a conversion Chart), or preferably, evacuate and charge by weight):
DeLorean R-12 Pressure Check Data (http://dmctalk.org/showthread.php?1244-Refrigerant-Temp-Pressure-Chart&p=13960&viewfull=1#post13960)
Standard 134a Pressure Check Data (http://acprocold.com/wp-content/uploads/2011/11/Temp-pressure-chart-33776F1.jpg)


Also,
The static pressure will tell you nothing useful about the correct charge, other than if it has some refrigerant. E.G. say a system takes 3 cans of R-134a. If you evacuate the system and add 2 cans, then let it sit overnight with an ambient of 76F, the static pressure will be ~80.2F. If you then add the 3rd can and check again the next morning, it will be 80.2F (yes, the same!) -- Static Pressure is a direct function of temperature.


EDIT- Oops, I just noticed Bitsy covered some of the above...
======

Kozmatic,
+1 on suspecting a bad low pressure switch (or you got it out of adjustment before you solved other problems).

[Kozmatic]

I used the parts cross-over list and Autozone had the LPS....I'm very happy to report that a quick install and all is well....AC works and cycles great! I put the gauges on it and she now shuts off at 20lbs and comes back on at 41lbs! I didn't make any adjustments to the replacement LPS. Plug and play! :biggrin::partyhat:

[artisticent]

Just reading through this thread and want to say that every response is so amazing in every way. The time and energy for all the help on this forum. It makes owning a Delorean even that much more incredible because it comes with a family. Im so excited to have my interior done and the few little things buttoned up so that I can drive to some events and meet more people in the D community. Just a kudos on how the members are so helpful to offer their knowledge.

Thanks
Nathan

[Kozmatic]

Just reading through this thread and want to say that every response is so amazing in every way. The time and energy for all the help on this forum. It makes owning a Delorean even that much more incredible because it comes with a family. Im so excited to have my interior done and the few little things buttoned up so that I can drive to some events and meet more people in the D community. Just a kudos on how the members are so helpful to offer their knowledge.

Thanks
Nathan

I couldn't agree more! It seriously is part of the reason I came back to Delorean for the second time