AC Low pressure adjustment?

[alexwolf1216]

Does anyone have the procedure to adjust the low pressure? I read in the shop manual but after a quick search found an old article that contradicts it.

I am cycling too much, it's maybe 10 seconds on, then it shuts off. The car started to get a little hot on the ride home, and it was only 81 outside. It's almost like the fans wouldn't come on long enough to cool down.

I know where the switch is and how to adjust, but what is the correct trigger/time to look for? It's 134a converted.

[David T]

Does anyone have the procedure to adjust the low pressure? I read in the shop manual but after a quick search found an old article that contradicts it.

I am cycling too much, it's maybe 10 seconds on, then it shuts off. The car started to get a little hot on the ride home, and it was only 81 outside. It's almost like the fans wouldn't come on long enough to cool down.

I know where the switch is and how to adjust, but what is the correct trigger/time to look for? It's 134a converted.

If it was fully charged and properly adjusted and now is cycling to fast you do NOT fix it by adjusting the switch. You probably have a leak and lost a little refrigerant. The fix is to find and fix the leak and refill with the correct amount of refrigerant.

[alexwolf1216]

I just replaced the switch. It was never properly adjusted, this was the first trial run of. The system.

[hmcelraft]

A new switch is already adjusted. If it is cycling too much there is a problem and highly unlikely it is the switch. Low on gas or system is clogged somewhere - I would suspect on the high pressure side. Orifice tube replaced? Have you checked the pressures with gauges yet?

[alexwolf1216]

I replaced the compressor, all lines, accumulator, orficice tube.

Testing pressure now actuallh

[alexwolf1216]

Pic with clutch engaged, max ac full fan EDIT pressure is building. Disregard.

33725

[alexwolf1216]

So pressure gets up to here on max fan

So33728



Something happens and it just drops. Clutch isn't stopping at all unless I turn down the fan. Then it cuts out for a quick second but reengages.

[alexwolf1216]

https://vimeo.com/124078699

Fan on max.

[alexwolf1216]

And of course now it's not cycling. It's just staying engaged the entire time.

[Bitsyncmaster]

When your car is not moving and engine at idle if your blower fan is on max it is common the compressor will not cycle.

My guess from your symptoms is the orifice tube is plugging up with junk. Did you flush your system. You may need to flush again.

[alexwolf1216]

Yea we flushed it, blew it out then pulled vacuum. Thanks guys!

[David T]

Yea we flushed it, blew it out then pulled vacuum. Thanks guys!

If you "just" replaced the switch and you KNOW you have the correct amount of refrigerant AND you converted to -134 the switch probably needs to be adjusted because it was set for -12.

[alexwolf1216]

Yes, the switch is brand new, filled with 3 cans of 134a. I can't seem to find adjustment procedures. In the manual it says it's already dialed in.

[Bitsyncmaster]

It's not that critical for adjustment. You just adjust it so your pull between 40 to 50 PSI on the lose side where the compressor will switch off. I think mine kicks the compressor on at 50 PSI and off around 40 PSI. If you adjust it to low you can cause the evaporator to ice up and then you get no cooling.

[alexwolf1216]

So if I can't get it to shut off while sitting, should I take it for s drive then adjust?

[PJ Grady Inc.]

I never adjust the LP switch as it causes erratic behaviour. From the 2nd picture of the gauges I'd suggest that your cooling fans are inop. or cutting out with the compressor engaged. The pressures are dangerously high and if it's not from overcharging then check those cooling fans. They must be on whenever the compressor is engaged or eventually the blowoff valve or something else will give way. Your clg. fan breaker may be cutting out under load...very common with the original breaker!
Rob


So if I can't get it to shut off while sitting, should I take it for s drive then adjust?

[David T]

I never adjust the LP switch as it causes erratic behaviour. From the 2nd picture of the gauges I'd suggest that your cooling fans are inop. or cutting out with the compressor engaged. The pressures are dangerously high and if it's not from overcharging then check those cooling fans. They must be on whenever the compressor is engaged or eventually the blowoff valve or something else will give way. Your clg. fan breaker may be cutting out under load...very common with the original breaker!
Rob


As Rob says, if EVERYTHING else is not running PERFECTLY you DO NOT adjust the pressure switch! The fans MUST run CONSTANTLY while the compressor clutch is engaged. In fact, to do it right, if the car is sitting still in a shop you should have a fan placed in front of the car blowing at the radiator to properly check the pressures. If you did not vacuum ALL of the air out your system before putting in the refrigerant, the pressures will be too high on both sides preventing cycling too. If the fans cycle while the clutch is engaged you probably have a bad CB. Did the car every get the relay upgrade kit?

[Bitsyncmaster]

So if I can't get it to shut off while sitting, should I take it for s drive then adjust?

You can bump up the engine speed and or drop the blower speed to get it to cycle. The low pressure switch is just that. If the AC unit is making more cooling than it needs it cuts off the compressor. The fact you did not get enough cooling on your drive at 81 deg air temp says your not getting enough cooling. Since the cycle was short I'm still thinking your orifice is limiting the cooling.

Your high pressure is also high and that depends on your cooling fans and the air temp you tested at.

I had to flush my condenser 2 or 3 times before my orifice would stay clean.

[alexwolf1216]

Sorry was out all day. I replaced my breakers and my cooling fans recently, DMC breakers and Toby fans.

If I have to flush my brand new orifice tube, that also means I will have to refill the system correct?

[DMC5180]

Sorry was out all day. I replaced my breakers and my cooling fans recently, DMC breakers and Toby fans.

If I have to flush my brand new orifice tube, that also means I will have to refill the system correct?

Yes, it will need to be refilled any time you break the system open. That what makes recovery units nice to work with. Unfortunately you don't have one of those but you could take the car to a shop and have the system emptied, then get a credit for the gas. I hate to intentionally let the gas out which is different than it leaking out.

The normal Cut IN should be 45 psi and Cut OFF 26-28 psi for 134a. When I had my system converted at an A/C shop the guy did adjust the LP down a little it was originally set at 30 psi for R12. I'm not sure what setting the high pressure switch cuts out at though. Obviously it must be very high since you were seeing 350 PSI an it still wasn't kicking the compressor off. Is it possible the 2 switches are in the the wrong locations. I don't what effect that would have on the system though. You definitely should not be seeing 60 psi on the low side, the normal full capacity for the 134a conversion is 1.95 Lbs. 3 full 12 oz cans is too much. Your looking for 32 oz approximately. Their is a formula that usually comes with conversion kits that states the percent by weight that you fill 134a compared too R12.

[Bitsyncmaster]

Another cause for poor AC is a plugged drain on the evaporator. But in most cases you would feel the passenger side carpet is wet if that was the case. That OEM drain hose sucks. I replaced my drain hose with a spark coil boot and clear hose running down below the frame.

[djdogbone]

The guys from "Today" flushed the lines with mineral spirits from the high to low side to clean to orifice tube without removing it (if I'm not mistaking)

http://m.youtube.com/watch?v=Fyy1Q7Wh57Q

[djdogbone]

I was wrong, from low to high side flushes the orifice tube.

[David T]

I was wrong, from low to high side flushes the orifice tube.

Anyone who knows the proper procedures to work on A/C will cringe while watching that video. Bill R is known for taking short-cuts and this video just confirms that. This video is a tutorial in what NOT to do. Besides, it has nothing to do with adjusting the low pressure switch. A proper flushing procedure is in the Workshop Manual N:10:12. A chart for adjusting the low pressure switch is on N:09:01 for R-12. If necessary the pressures and temperatures can be converted over to -134. Be aware that when using -134 you must use 10% less by volume and your head (high side) pressures will be MUCH higher (low side pressures too). Any leaks will be made all that much worse because of the higher pressures and you lose about 10% cooling capacity. The system was not designed to use -134, the condenser is too small.

[djdogbone]

http://youtu.be/-RvNS7JfcMM

[Farrar]

I had a similar problem to yours when I was working on my a/c a couple of years ago -- turns out I had accidentally installed the orifice tube backwards.

[alexwolf1216]

Well that's interesting. Can it go in both ways?

[Farrar]

Can it go in both ways?

Technically, yes -- but once you put it in the correct way, you will realize it. The fit is much tighter.

[Bitsyncmaster]

Technically, yes -- but once you put it in the correct way, you will realize it. The fit is much tighter.

It will work either way but it's best to have the filter screen before the orifice gets liquid coolant. And the pulling end is made with ears on the correct install.

[hmcelraft]

So pressure gets up to here on max fan

So33728



Something happens and it just drops. Clutch isn't stopping at all unless I turn down the fan. Then it cuts out for a quick second but reengages.

That symptom sounds like "slugging" which could be the result of too much gas or a missing or wrong size orifice tube and/or too much oil. That compressor stopping may be a liquid lock (slugging). Slugging can destroy the compressor. The DeLorean ac systems are rather forgiving - but, be careful in oil and gas measurements. You're sure you are using the right weight and type of oil?

[alexwolf1216]

The oil was filled in the compressor shipped by DPI. Josh confirmed that it was the proper oil

[DMC5180]

The oil was filled in the compressor shipped by DPI. Josh confirmed that it was the proper oil

sanden pre-oils all new compressors. Their is no need to add any additional amount.

At my work we new AC on our product. The only time oil is added is if system maintenance is being performed and oil is removed during the recovery process. Then only the amount removed will be replaced.

[alexwolf1216]

I should correct myself for clarity. Josh told me the compressor was properly filled and ready to go, not that he put anything in or removed anything from.

[hmcelraft]

So pressure gets up to here on max fan

So33728



Something happens and it just drops. Clutch isn't stopping at all unless I turn down the fan. Then it cuts out for a quick second but reengages.

Just looking at the gauges - they tell me one of several things could be happening that I would investigate first because the pressures appear too high.
1. inadequate air passing over the condenser. Check the fans for proper operation. Fins in condenser are clear?
2. too much gas. Get the correct charge into the system. Drain and start over.
3. too much oil. Take the compressor off - drain the oil - measure the drained oil and do the calculations for 8-9 oz of oil for the system. Put balancing amount of oil back in the compressor reinstall and recharge. Need to be cautious here. You might want to take the accumulator off and drain any oil from it if you suspect a lot of excess oil was put into the system initially.
4. The air temp is 125F and all is well.

[alexwolf1216]

Just looking at the gauges - they tell me one of several things could be happening that I would investigate first because the pressures appear too high.
1. inadequate air passing over the condenser. Check the fans for proper operation. Fins in condenser are clear? New fans, new breakers but I heard one pop after about 45 mins of operation. Fins clear
2. too much gas. Get the correct charge into the system. Drain and start over. Put in exactly 3 cans, +- a little at the end
3. too much oil. Take the compressor off - drain the oil - measure the drained oil and do the calculations for 8-9 oz of oil for the system. Put balancing amount of oil back in the compressor reinstall and recharge. Need to be cautious here. You might want to take the accumulator off and drain any oil from it if you suspect a lot of excess oil was put into the system initially. Sure hope not......
4. The air temp is 125F and all is well. This made me chuckle. I do live in the oven called Texas, but it was 80 outside. I wonder if the pressure drop was from the HPS kicking in?


Responses above

[hmcelraft]

Just looking at the gauges - they tell me one of several things could be happening that I would investigate first because the pressures appear too high.
1. inadequate air passing over the condenser. Check the fans for proper operation. Fins in condenser are clear? New fans, new breakers but I heard one pop after about 45 mins of operation. Fins clear
2. too much gas. Get the correct charge into the system. Drain and start over. Put in exactly 3 cans, +- a little at the end
3. too much oil. Take the compressor off - drain the oil - measure the drained oil and do the calculations for 8-9 oz of oil for the system. Put balancing amount of oil back in the compressor reinstall and recharge. Need to be cautious here. You might want to take the accumulator off and drain any oil from it if you suspect a lot of excess oil was put into the system initially. Sure hope not......
4. The air temp is 125F and all is well. This made me chuckle. I do live in the oven called Texas, but it was 80 outside. I wonder if the pressure drop was from the HPS kicking in?


Responses above

Well - 3 cans of 134a at 12oz is 36oz + a little at the end? That is 4oz + too much. Enough in my book to get the high pressures and poor performance..

[alexwolf1216]

Well - 3 cans of 134a at 12oz is 36oz + a little at the end? That is 4oz + too much. Enough in my book to get the high pressures and poor performance..

Yeah I think they were 12oz. I read somewhere and was advised that the car could take all 3 cans. So, should I just open one of the scrader valves (red or blue) and let some out?

[David T]

[QUOTE=alexwolf1216;170245]

Well - 3 cans of 134a at 12oz is 36oz + a little at the end? That is 4oz + too much. Enough in my book to get the high pressures and poor performance..

According to ST-29-11/81 the proper fill using R-12 is 2.2 lbs or 35.20 oz. Just short of 3 cans. Using R-134 you should use 10% less by volume so you should only put 31.68 oz of -134 in. When converting to -134 you are supposed to change the service ports and put a new label indicating the conversion and the proper amount of fill besides also flushing the system, replacing the accumulator/dryer, and changing the oil. All of the "O" ring seals and hoses should also be replaced.

[alexwolf1216]

All ports, orings,hoses and compressor we're replaced.

[hmcelraft]

You can bleed some gas off. That process may not be that accurate but, if you leave the gauges attached, you can probably get close. I would shoot for a 35-40 lbs reading on the low side pressure if the temp outside is 80F. The high side pressure should be below 300lbs. - hard to say if no auxiliary fan is in front of the car. You may want to shoot for 40-45lbs to start and see what you get - then go from there.

[alexwolf1216]

You can bleed some gas off. That process may not be that accurate but, if you leave the gauges attached, you can probably get close. I would shoot for a 35-40 lbs reading on the low side pressure if the temp outside is 80F. The high side pressure should be below 300lbs. - hard to say if no auxiliary fan is in front of the car. You may want to shoot for 40-45lbs to start and see what you get - then go from there.

Those readings were taken when the car was pulled nose first into the garage. Also, the pressure changed a bit, raising and lowering. At what poing do I measure?

[Farrar]

Get a box fan and set it in front of your car, facing the grille, turned on to the highest speed. This will pass air over the condenser, simulating (but not replicating) driving while using the air conditioning. See what readings you get then.

[hmcelraft]

When testing - RPM should be 2000 to 2400 rpm. I use 2200. Use a piece of small wood to wedge the throttle open to set the rpm or have some help run up the rpm. The low pressure should modulate some. To start, try 40-45 lbs. Check the outlet temp. Is it close to 40-45F? stop. Above? bleed out some more gas and shoot for 35-40 lbs. modulation. Closer to 40F? stop. Is high pressure 250-275 lbs. or lower. you're good. If not - you could bleed off some more gas and shoot for 30-35 lbs. modulation. You're probably getting close to the correct amount of gas in the system at 40 to 45F outlet temperature. A close temp but over 40 to 45F will probably get lower once on the road. The compressor should cycle occasionally - maybe. If frequent cycling begins that will indicate the system probably went low system on gas.

[Ron]

At what poing do I measure?See note at bottom of this chart (http://dmctalk.org/showthread.php?1244-Refrigerant-Temp-Pressure-Chart&p=13960&viewfull=1#post13960).

=====

$02
The problem probably relates to this symptom (or ls what is hiding it)....

The car started to get a little hot on the ride home, and it was only 81 outside. It's almost like the fans wouldn't come on long enough to cool down.

Ensure the fans are always on whenever the compressor is on, the engine is at normal temps (use a box fan in front of the radiator if needed), and compare to the chart in the link above

[kings1527]

Here's a video I did a couple of years ago that goes through the entire process of adjusting the LP switch. This might help you. My AC is perfect in my car It's a very easy adjustment to do once you know how to do it and have the right equipment (as always). Once it's set, you shouldn't have to touch it again even if you evac the system and refill it (provided you use the same refrigerant).

https://youtu.be/lt1oarL0soE