Need some A/C help

[Ccmano]

A/C is not my strong suit and this one has me stumped. Recently replaced the condenser, accumulator/drier, orifice tube and compressor hoses. Evacuated the system for 30min and vacuum held. Charged the system with 30oz. R134a and 4.5oz PAG100. The compressor runs and the system cools but only down to about 55 degrees outlet temp at idle.

Now here's the really strange part. The low side pressure is in the mid 30psi range, about right from what I understand. The high side is zero! The system generates so much heat at the condenser that the car cannot idle indefinitely on a 90 degree day with the AC on. Coolant temps just keep climbing with fans coming on a 203 degrees.

I'm thinking bad compressor and/or obstruction on the high side. Strange that high side pressure is zero but the compressor runs and there is some cooling.

Thoughts?
H
:cheers:

[Tripler]

Sounds like an obstruction to me .
Been a while but I am a retired HVAC mechanic , not a car AC guy but zero highside is usually a pinched or blocked liquid line .


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[Tripler]

Did you also pressure test the system with nitrogen for a 1/2 hr or so ? And flush the system with nitrogen before adding 134a ? There could still be moisture in the system even tho you put a vacuum on the system to pull the moisture out . This is what I did on residential .
Oh and also , when assembling connections , did you use a bit of refrigerant oil or vacuum pump oil to lube the connections ? That's important for a good seal because of aluminum binding against itself , even the brass connections will need lube .

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[ram_g]

Apologies in advance if this is an insulting suggestion, but are you sure you have communication between your high side schrader valve and your gage set? What are the pressures with the engine off and the car having set for a while? Under these conditions the low and high side pressures should be the same as it will equalize in several minutes if nothing is running. If you see these same pressures then at least you would have positively answered the question.

[Ccmano]

Apologies in advance if this is an insulting suggestion, but are you sure you have communication between your high side schrader valve and your gage set? What are the pressures with the engine off and the car having set for a while? Under these conditions the low and high side pressures should be the same as it will equalize in several minutes if nothing is running. If you see these same pressures then at least you would have positively answered the question.

That has been a question in my mind as well. I suspect there is an issue with the Schrader valve, the R134 fitting adapter and the quick coupler on the high side. I have tested the gauges on two other cars (one with a similar adapter) and high side readings are normal. I agree that I should see equalization after shut down, but I don't. Just this evening I depressed the high side Schrader valve manually and a spray of pressurized refrigerant came out which tells me I should be getting a pressure reading. I suspect the pintel of the Schrader valve sits too low once the adapter is screwed on for the Coupler to engage it. Not sure what to do about that. It worked fine on the other car with a similar adapter I tested. Either there is an issue with this adapter or the wrong Schrader valve has been installed with a short pintel. I'll pick up a different adapter tomorrow.
H
:cheers:

[Ccmano]

Did you also pressure test the system with nitrogen for a 1/2 hr or so ? And flush the system with nitrogen before adding 134a ? There could still be moisture in the system even tho you put a vacuum on the system to pull the moisture out . This is what I did on residential .
Oh and also , when assembling connections , did you use a bit of refrigerant oil or vacuum pump oil to lube the connections ? That's important for a good seal because of aluminum binding against itself , even the brass connections will need lube .

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Thanks for your input. I don't have the equipment to do a nitrogen pressure test and flush. Thanks for the tips about lubing the connections. From the looks of things I will be taking things apart again and starting fresh. As noted on my previous post I suspect there is an issue with the high side connection to the gauges.
H
:cheers:

[Marc Haibeck]

Hi Hans,

Both of the cooling fans should turn on within 30 seconds of turning on the compressor. There is a fan switch on the high pressure line. It's the smaller of the two switches by the dipstick. The switch opens when the pressure goes to 240 psi. As a test, if the connector is removed the fans will turn on.

At 55 degrees at the center duct the performance might be normal. Generally the system should cool to the ambient temperature - 35 degrees. The '90 and '91 service manuals have a performance rating chart. Look up the ambient temperature and humidity on the chart.

[Ccmano]

Update, as suspected the high side quick coupler does not engage the Schrader valve because once the adapter is installed the Schrader valve sits too deep. I found a work around and now have both high and low pressures. High side is ~260psi and low side is ~32psi with a center vent temp ~45degrees on an 90degree ambient day. So all of that looks within spec. The only issue that remains is that the pressures do not equalize, not even overnight. High side drops the ~110psi and low to ~25psi.

What remains a major issue is the unabated climb in coolant temp with the AC on at idle. When driven without stopping the temps stay normal. The temps rise after a few minutes of driving in stop and go traffic so that the coolant temps are already over 230 and rising. Both fans come on when the AC is turned on per spec. Once the AC is off temps return to normal no matter what the ambient temps. Both the radiator and the condenser have now been replaced. Both needed it as they were badly clogged with sand a grit. The accumulator/drier and orifice tube have been replaced as well.

So I'm thinking the lack of equalization and the high temps are related, probably an obstruction of some sort.
Thoughts?
H
:cheers:

[ram_g]

Yeah, I've been googling this out of curiosity and everything I see says the pressures should equalize in a car ac system. So I would also lean towards an obstruction somewhere. Which may be a serious hassle as you'd have to discharge the system and break things down to isolate where. Ugh.

Personally, I would start with the orifice tube.

[XfireZ51]

I was thinking orifice tube as well. When I re-did mine. I found it was installed incorrectly. Was a bitch to get out.

[jss06c6]

Hans, definitely sounds like you have a blockage somewhere. That system should equalize in the 90 - 95 psi range overnight. How did the screen look when you replaced it? Normal to have some debris, but should be trapped in the filter. It sounds like you've got some garbage in the system somewhere. Probably need to get another dryer after you flush the system too.. hopefully not trapped in the evaporator..

Clean it, get proper oil charge in it, pressure test and then nice long vacuum test. Watch overnight to make sure you don't lose more than 2-4 psi (temperature drop in desert!) And go for it again.

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[Ccmano]

Hans, definitely sounds like you have a blockage somewhere. That system should equalize in the 90 - 95 psi range overnight. How did the screen look when you replaced it? Normal to have some debris, but should be trapped in the filter. It sounds like you've got some garbage in the system somewhere. Probably need to get another dryer after you flush the system too.. hopefully not trapped in the evaporator..

Clean it, get proper oil charge in it, pressure test and then nice long vacuum test. Watch overnight to make sure you don't lose more than 2-4 psi (temperature drop in desert!) And go for it again.

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Steve, the old orifice tube that came out was surprisingly clean, just a small bit crud on it. Yes, looks like I'll have to pull it apart again. I'm hoping it's just the orifice tube. However it was doing the high heat thing before I changed the condenser. It will be next weekend before I can get to it.
H
:cheers:

[Ccmano]

Update, the car has been sitting for a week or more. I've been busy with other things. Went out today and hooked up the AC gages to the car. Car was not running ambient temp~90 degrees 30 percent humidity. Surprisingly the static pressures had equalized to ~100 psi which according to the manual is correct. I started the car and after warm up running at 2000 rpm Low side was ~27psi, high side ~290 psi, and the duct temp inside the car came down to ~43F. All of this is normal according to the manual. I turned off the car and for the first time the high and low sides started equalizing immediately, but slowly. Also normal. I didn't drive it, probably should have. Will do that tomorrow.

What continues to baffle me is that the compressor is not cycling Off and on, it just stays on. According to the manual it should (under the correct circumstances) cycle. Most importantly, and the reason I'm doing all this is that with the AC on the coolant temps rise unchecked if I drive in traffic or let it idle for an extended period. The car has a new aluminum 3 core radiator, new condenser, accumulator/drier and orifice tube. Both fans come on with the AC on.
That can mean only 2 things, either the condenser is dumping so much heat the cooling system can't keep up (which begs the question, why, compressor not cycling?) or the cooling system is some how compromised and can't handle the extra heat. Tho... with the AC off there are no cooling issues at any temperature and now with the new radiator it runs even cooler.

I've emptied and refilled the cooling system multiple times for various reasons but the car has always behaved this way. So I'm inclined to think an air bubble is not the issue. I suppose a thermostat that doesn't fully open is a possibility. However I'm still not convinced the AC system is operating correctly. Heck two weeks ago I would have thought the AC had a blockage.

Oh and stupid question to which I can't find an answer.... the orifice tube goes into the evaporator tube long side down, correct? That's the way the old one came out, but I have read that in older GM CCOT Systems it went in short side down.

Your input is encouraged.
H
:cheers: