a/c Mystery

[DMCflux]

I went for a 45 min drive to my destination the other day. The temp outside was 90 with 90% humidity (uncomfortable day). I decided it was a good day to test out my D's a/c and engine temp. I have a DMCMW a/c kit installed (evap, hign & low temp switches, oraface tube), R12 and I know the system is holding pressure and I have no leaks. After 10 min of driving (all freeway miles to destination) the thermometer I have in my vents started to increase. By the time I got off the freeway, the a/c was blowing at 70 deg. On my ride home, everything was normal and the a/c was working fine. Any thoughts???

[Michael]

It's possible your evaporator froze up. Do you hear the compressor cycle?

Driving on the interstate with lots of fresh air over the condenser will make the ac as cold as it can get, as you slow down and rely on the fans more, the ac will warm up a bit..

[DMCMW Dave]

Either slightly overcharged, the low pressure switch set a bit too low, or an odd combination of circumstances as mentioned. Were you on normal or max? I agree that it sounds Iike the evaporator froze up. When you shut it off, it defrosted and was back to normal.

[DMCflux]

Either slightly overcharged, the low pressure switch set a bit too low, or an odd combination of circumstances as mentioned. Were you on normal or max? I agree that it sounds Iike the evaporator froze up. When you shut it off, it defrosted and was back to normal.

I dont think it froze because prior it was blowing around 47 deg. How do I adjust the low pressure switch?
I was on max

[DMCflux]

I remember when I got off the freeway, I was in some traffic. A/c was on max and I saw the engine temp gauge incr and felt the fans kick in. So did the high press switch cut the voltage to the fans while on the freeway? This is the first time it has happened and the first drive on a 90 deg day.

[Ron]

No, the high pressure switch should only turn the compressor off.

Is 47F the coldest it blows? If so, I doubt it is the evaporator freezing, assuming your duct work etc is in good shape...more likely trash or moisture at the orifice tube.
There are really too many things it could be to even guess w/o putting a gauge set on it.....

[DMCflux]

No, the high pressure switch should only turn the compressor off.

Is 47F the coldest it blows? If so, I doubt it is the evaporator freezing, assuming your duct work etc is in good shape...more likely trash or moisture at the orifice tube.
There are really too many things it could be to even guess w/o putting a gauge set on it.....

No, it usually blows colder. On that particular day it was really hot and the humidity was extremely high.

[David T]

No, it usually blows colder. On that particular day it was really hot and the humidity was extremely high.

Not only can you freeze the exterior of the evap coil with condensate, if there is ANY moisture internally (with the refrigerant) the orifice tube can freeze up stopping the flow of refrigerant and shutting the compressor off by either the low or high pressure switch. That is why you pull a hard vacuum for a while, to boil out any remaining water vapor before charging with refrigerant. If the evap coil freezes over you will notice significantly diminished air flow out the vents. if it continues and the safety switches do not shut the compressor off in time you can blow the relief valve.
David Teitelbaum

[DMCflux]

Not only can you freeze the exterior of the evap coil with condensate, if there is ANY moisture internally (with the refrigerant) the orifice tube can freeze up stopping the flow of refrigerant and shutting the compressor off by either the low or high pressure switch. That is why you pull a hard vacuum for a while, to boil out any remaining water vapor before charging with refrigerant. If the evap coil freezes over you will notice significantly diminished air flow out the vents. if it continues and the safety switches do not shut the compressor off in time you can blow the relief valve.
David Teitelbaum

After installing the new equipment I had a vacuum on it for over an hour to get any moisture out of the system. The orafice tube freezing makes sense but I don't think I have any moisture in the system right now.

[DMCflux]

Could the orafice tube supplied with the kit be the wrong one for a system using R12?

[Bitsyncmaster]

My bet is your drain is plugged. After the trip, it was filled with water and no air could pass over the evaporator.

[DMCflux]

My bet is your drain is plugged. After the trip, it was filled with water and no air could pass over the evaporator.

Drain plug is clear. I made sure to blow out any debris when I had it all apart. I can see the condensation pool under the car on humid days.
Im thinking there may be dirt in the system that temporarily blocked the orafice tube. I might try flushing it.

[David T]

Drain plug is clear. I made sure to blow out any debris when I had it all apart. I can see the condensation pool under the car on humid days.
Im thinking there may be dirt in the system that temporarily blocked the orafice tube. I might try flushing it.


I would strongly doubt it is dirt, there is a large filter just ahead of the orifice to prevent that. Moisture is the much more likely cause. If I am correct you should remove the refrigerant and oil, flush the system, replace the dryer/accumulator, leak test, and pull a hard vacuum for at least an hour. Then refill with a measured amount of Freon. If the system looks contaminated visually, corroded, residue, etc) you should flush several times.
David Teitelbaum

[DMCflux]

I would strongly doubt it is dirt, there is a large filter just ahead of the orifice to prevent that. Moisture is the much more likely cause. If I am correct you should remove the refrigerant and oil, flush the system, replace the dryer/accumulator, leak test, and pull a hard vacuum for at least an hour. Then refill with a measured amount of Freon. If the system looks contaminated visually, corroded, residue, etc) you should flush several times.
David Teitelbaum

I'll try flushing it. The accumulator was replaced when I did the kit. I then pulled vacuum for an hour and pressured the system and monitored it for 2 days with no signs of lost pressure.

[Ron]

I agree with David, but I would sure put a set of gauges on it and reproduce the symptoms before opening it up.

[DMCflux]

I agree with David, but I would sure put a set of gauges on it and reproduce the symptoms before opening it up.

Agree.
Thanks for everyones help!

[DMCflux]

Update:

Guages show everything is fine. Driving freeway speed for 30+ min. With a/c on max and the fans shut off & temp begins to increase.
Does anyone know why this happens? (Fans shutting off)

[DMCMW Dave]

Update:

Guages show everything is fine. Driving freeway speed for 30+ min. With a/c on max and the fans shut off & temp begins to increase.
Does anyone know why this happens? (Fans shutting off)

Circuit breaker overheating (assuming the fans shut off but the compressor is still running). It is a self-resetting breaker. It's either a bad breaker or a fan motor that's pulling too much current. When this happens your A/C pressures absolutely take off (which is probably why a hose blew a few weeks ago).

[DMCflux]

Circuit breaker overheating.

What do I do to solve the problem?

[David T]

Update:

Guages show everything is fine. Driving freeway speed for 30+ min. With a/c on max and the fans shut off & temp begins to increase.
Does anyone know why this happens? (Fans shutting off)

It is very possible for the fans to shut off when the compressor cycles. When you are moving and the otterstadt is not making the cooling fans run and the compressor shuts off during it's cycle the fans will stop till either the otterstadt runs the fans or the compressor starts up again. Or maybe the compressor is shutting down on it's high (or low) pressure switch because the orifice is frozen again.
David Teitelbaum

[DMCflux]

It is very possible for the fans to shut off when the compressor cycles. When you are moving and the otterstadt is not making the cooling fans run and the compressor shuts off during it's cycle the fans will stop till either the otterstadt runs the fans or the compressor starts up again. Or maybe the compressor is shutting down on it's high (or low) pressure switch because the orifice is frozen again.
David Teitelbaum

When the fans shut off with the ac on, they do turn back on when engine temp reaches its point to have the otterstadt run the fans.

[DMCMW Dave]

What do I do to solve the problem?

You need to figure out if it is a bad breaker or a bad fan.

Measure the fan current to see if it's more than the breaker can tolerate. Measure each fan separately and see if one is pulling way more than the other. This should be a 40A Breaker, total load of the two fans once they are up and running should not be more than about 25A. If you have the breakers reversed (i.e. the big one on the blower and the small one on the radiator fans) this could happen too.

[DMCMW Dave]

When the fans shut off with the ac on, they do turn back on when engine temp reaches its point to have the otterstadt run the fans.

With the compressor still engaged? If so, that's pretty odd behavior, the only other thing in the circuit is a diode between the compressor and the fan circuit. Diodes never fail like this, when they go bad they stay bad.

[DMCflux]

With the compressor still engaged? If so, that's pretty odd behavior, the only other thing in the circuit is a diode between the compressor and the fan circuit. Diodes never fail like this, when they go bad they stay bad.

Not sure if the compr is still engaged. I'll check the fan current. Thank you Dave!

[DMCflux]

Looking in the fuse/relay area, the 40 & 30 amp breakers are switched. The 30 has two wires going to it and the 40 has four.

[DMC5180]

Just too clarify things a bit.

Steve, Since You have verified the fans DO run with the OtterStat (that's GOOD) Do you have OEM fans or DPNW Fans?

Start the cold engine. Turn the A/C on MAX/ fan speed 4/ the the compressor clutch should cycle ON, it may not cycle OFF at idle, raise the RPM until it does cycle. The fans Should be running in unison ON/OFF with the comp. clutch. If the fans do not run with the clutch check the DIODE Dave mentioned It will be the one with the (Pink) wire and Doubled (BLACK/orange) wires (It may Have failed OPEN) That DIODE was Failed OPEN on my car when I first got the car. I had taken the car in to the A/C shop for servicing and the Guy said the fans would not RUN when the compressor was running. I traced it to that DIODE. You can Temporarily remove the the DIODE and connect the wires together. This will allow you to see if the fans RUN and is an easy verification of an open DIODE. You do not want to drive the car like this though. The compressor will engage IF the Otterstat kicks in.

[DMCflux]

Just too clarify things a bit.

Steve, Since You have verified the fans DO run with the OtterStat (that's GOOD) Do you have OEM fans or DPNW Fans?

Start the cold engine. Turn the A/C on MAX/ fan speed 4/ the the compressor clutch should cycle ON, it may not cycle OFF at idle, raise the RPM until it does cycle. The fans Should be running in unison ON/OFF with the comp. clutch. If the fans do not run with the clutch check the DIODE Dave mentioned It will be the one with the (Pink) wire and Doubled (BLACK/orange) wires (It may Have failed OPEN) That DIODE was Failed OPEN on my car when I first got the car. I had taken the car in to the A/C shop for servicing and the Guy said the fans would not RUN when the compressor was running. I traced it to that DIODE. You can Temporarily remove the the DIODE and connect the wires together. This will allow you to see if the fans RUN and is an easy verification of an open DIODE. You do not want to drive the car like this though. The compressor will engage IF the Otterstat kicks in.

oem fans. they do run with the clutch when a/c is turned on and off if i shut it off. I think the breakers are wrong as Dave mentioned. the 4 wire leads are going to the 40 amp and the 2 lead wires are going to the 30. Im thinking this is where my problem is. The fans drawing to much current on the wrong breaker, shutting the fans off until the cars otterstadt turns them back on when engine reaches a certain temp. I will switch the breakers and see what happens.

[DMCMW Dave]

oem fans. they do run with the clutch when a/c is turned on and off if i shut it off. I think the breakers are wrong as Dave mentioned. the 4 wire leads are going to the 40 amp and the 2 lead wires are going to the 30. Im thinking this is where my problem is. The fans drawing to much current on the wrong breaker, shutting the fans off until the cars otterstadt turns them back on when engine reaches a certain temp. I will switch the breakers and see what happens.

Yes, that sounds backwards. The 40A breaker should have 2 wires only (i.e. coming from the cooling fan relay and going to the blue socket).

The 25 A (sometimes 30A) breaker has one input and two outputs, one each for the speed 3 and 4 relay. In addition what looks like a second input side is the feed to the starter recall. That's unrelated to your issue but it is important that the blower breaker have both relays on one side, or you'll have a unfused fan speed.

Also note that the breakers are marked for input/output, or source/load etc. They should be connected the right way or they may pop at lower than rated current. Not sure why, but . . .

[DMCflux]

Yes, that sounds backwards. The 40A breaker should have 2 wires only (i.e. coming from the cooling fan relay and going to the blue socket).

The 25 A (sometimes 30A) breaker has one input and two outputs, one each for the speed 3 and 4 relay. In addition what looks like a second input side is the feed to the starter recall. That's unrelated to your issue but it is important that the blower breaker have both relays on one side, or you'll have a unfused fan speed.

Also note that the breakers are marked for input/output, or source/load etc. They should be connected the right way or they may pop at lower than rated current. Not sure why, but . . .

I switched the circuit breakers and the fans stay on now. That problem is solved. I still have a fluctuation in ac temp and pressure. I threw guages on and it showed my pressure at 32 so I took some out to the manuals recommended spec. Went for a ride, threw guages on, now at 20. Evap was iced over. I waited for the evap to de ice and went for another ride, pressure at 40! The readings are all over the place as is the cabin temp. I start out at 42 and after 30min of drviing I'm at 65.

[Ron]

It is normal for the pressure to fluctuate and 32psi is not abnormal when it is 70-100F...Are you taking the readings at the moment the clutch kicks off?
What was the high side showing?

[Bitsyncmaster]

You really can't determine the AC charge by checking the low pressure. The best way to charge is to evacuate and charge with a measured amount. Most will top up the charge using the high pressure reading and a thermometer in the vent.

[DMCflux]

It is normal for the pressure to fluctuate and 32psi is not abnormal when it is 70-100F...Are you taking the readings at the moment the clutch kicks off?
What was the high side showing?

It's 85 today. I took the readings after driving for 30 min.
What should the high and low side be and at what rpm?

[Ron]

IMHO, you have to use both if you don't want to evacuate it....and there is a chart at N:09:01 to do it with.

EDIT:
20422

[DMCflux]

IMHO, you have to use both if you don't want to evacuate it....and there is a chart at N:09:01 to do it with.

EDIT:
20422

Thank you, Ron.

[DMCflux]

What are the chances I have a bad or plugged orifice tube?

[Ron]

NP!

Make sure you take the readings when coolant is within normal temp range (use a box fan in front of the radiator if you have to).

[Ron]

What are the chances I have a bad or plugged orifice tube?Then you should see the low side go low (until the pressure switch kicks the compressor out) while the high side goes high...

[David T]

You do not want the low side pressures to go below 32 PSI for any length of time (assuming you are using R-12). At 32 (or below) the evap coil will start to ice up.
David Teitelbaum

[Texas Twister]

I had a stepped orifice in mine for awhile and it was nothing but a headache. I use the white fixed orifice by GM. About 2 bucks at the parts store. Be sure the pressures are good. I was told too low can cause freezing up too.

[Texas Twister]

If it is plugged it won't get better! I had this happen due to me not flushing out the condenser when I replaced everything else.

[DMCMW Dave]

What are the chances I have a bad or plugged orifice tube?

Slim. That generally won't freeze up the evaporator. Classically a frozen evaporator is symptom of overcharge or a low pressure switch set too low. That switch is variable.

[DMCflux]

Slim. That generally won't freeze up the evaporator. Classically a frozen evaporator is symptom of overcharge or a low pressure switch set too low. That switch is variable.

if the switch is set to low which way do I turn the screw to adjust it?

[David T]

if the switch is set to low which way do I turn the screw to adjust it?

You should not touch that adjustment unless:
You KNOW all of the components of the A/C are working correctly
You measure in the correct amount of refrigerant
You set up the pressures right

NOW you adjust the switch to give you the right cycle time.
If it has never been touched it is probably right and something else is not right. Do NOT adjust that switch to correct for something else that is not right.
David Teitelbaum

[DMCflux]

You should not touch that adjustment unless:
You KNOW all of the components of the A/C are working correctly
You measure in the correct amount of refrigerant
You set up the pressures right

NOW you adjust the switch to give you the right cycle time.
If it has never been touched it is probably right and something else is not right. Do NOT adjust that switch to correct for something else that is not right.
David Teitelbaum

the compressor doesn't cycle, all the components of the AC system are new, including low pressure switch

[DMCMW Dave]

the compressor doesn't cycle, all the components of the AC system are new, including low pressure switch

The compressor HAS to cycle or the evaporator will freeze up. Which seems to be what you are seeing.

The adjustment is between the two pins of the switch. If it never cycles this may be the problem (unless someone has bypassed the switch in some way that you are not seeing). If not, you have another issue to solve first. I've seen some POs that think the switch is bad when the system is actually out of refrigerant, so they jumper it out in any number of creative ways. This usually leads to compressor failure. Counterclockwise is lower pressure. Whole range of adjustment is normally less than a turn, so if you are moving it more than that something is wrong. Unplug the switch and see if the compressor stops.

I can honestly say I've never seen one of those switches bad (or out of adjustment) out of the box, but anything is possible.

[Ron]

It makes no sense at all to play with the orifice tube adjustment unless you know the charge is correct. The most you could know is that the pressures are OK for whatever the ambient temperature is at the time you set it.

My suggestion is that you stop, take a deep breath, and tell us everything from the beginning, including: how it was originally charged ie what kind, how much, how evacuated, if you know; from first symptoms, what you did to resolve them, the results, etc; and not leave anything out that you might think doesn't matter, blown hose, variable orifice tube etc; and, your current readings for everything in the chart. We need the whole story to help you get it right.
And hang in there! ;-)

[DMCflux]

Problem solved:

It turned out to be a bad/stuck low pressure switch. I put in a new one and the compressor now cycles and the evap doesn't freeze.
Thank you everyone for your help. :smile: