Need some A/C help
 

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:

Re: Need some A/C help
 

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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Re: Need some A/C help
 

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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Re: Need some A/C help
 

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.

Re: Need some A/C help
 

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:

Re: Need some A/C help
 

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:

Re: Need some A/C help
 

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.

Re: Need some A/C help
 

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:

Re: Need some A/C help
 

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.

Re: Need some A/C help
 

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