Hi again,

My AC was going out about a year ago and I found the compressor was going bad. I changed the low pressure switch, the orifice filter (looked fine) and some of the o-rings. Everything worked great for a year or so but it started getting warmer. When I checked the pressure I noticed the low side wasn't holding much pressure. I figured there must be a leak somewhere but I couldn't find anything with the UV light. I recharged the system and it seemed fine again. Months later on I noticed the clutch started kicking on and off a lot even when the AC was not putting out much cold air, it kept kicking off until it finally stopped kicking on and nothing but warm air.

Looking at the pressure it seems the high side and low side are almost equal at about 80 psi. That's way high on the low side from what I normally see of about 44psi (low) vs 150psi (high). They seem to both be sitting around 80 psi. My thought is the high side is leaking into the low side. Is that the expansion valve? Or could it be the condenser is shot?

This is a 2002 4.0L by the way, so it's a bit old.

Any ideas of what to troubleshoot? Oddly when I release the fittings there doesn't seem to be any fluid, it feels like hot warm air.

Thanks,
Eric

 

Did you flush and vacuum the system before installing new compressor and receiver/drier
A failing compressor will send out metal bits into the Condenser and they will slowly work their way around the system causing blockages and even 2nd compressor failure if they get into the low side
But yes they can clogged the filter and even cut it and get thru to expansion valve clogging it

How AC works is pretty simple
Any one thats had an air compressor knows it runs hot but when you release the compressed air the air gets very cold as it expands from being compressed

AC systems do the same thing but they use a fluid that has a better temperature differential, and its only a fluid when under pressure
Compressor does just that, compresses the fluid which gets it very HOT, the hot fluid which can turn back into a gas, goes into the condenser, in front of radiator
This is the high pressure side
It then goes to expansion valve where pressure is allowed to expand and(like with compressed air) it gets very cold as it expands, that cooling happens in the evaporator inside the heater box
Fan blows air thru the evaporator(like heater core) and the air is cooled, now its in the low pressure side and travels back to compressors inlet pipe to be re-compressed

 

Hi. Yes I flushed and vacuumed it down for about an hour and weighted it upon refilling. I'm pretty familiar with how the system works from doing the previous repair. I don't think the compressor was originally damaged (also the filter was clean) however there was no refrigerant in the system so decided it was a good chance to replace it along with several other parts where the UV showed possible leaks.

I think this problem is related to the expansion valve or condenser but I'm looking for some way to further troubleshoot it because it takes forever to get parts.

 

Does anyone have some thoughts on why it appears the high side is leaking into the low side? I saw an A/C repair video on youtube that talked about this case and what to do, but I can't find it again. Thanks.

 

buddy the pressures are equal because the compressor ISN'T running. You need to track down why it isnt running. You gotta find out if its getting the 12v to activate the AC clutch. Also good job @RonD on explaining how AC works. The issue in this one is the compressor isnt kicking on, or is destroyed again. Its not an expansion device issue, that wouldnt make these symptoms

 

Buddy, I forced the compressor on as well and it appears the high side is leaking into the low side. Likewise when I change the low side pressure the high side appears to track it up or down. I guess I'll just work on this issue on my own.

 

how did you know the compressor was on? If you think the high side is "leaking" into the low side, then quit screwing around and get the expansion device replaced

 

Well when compressor is off there is no high or low side the pressure should be equal
There is no shut off for expansion valve so high pressure just goes thru it until both "sides" are equal

Only when compressor is on will the "high side" get high because compressor compress's the "freon" faster than expansion valve can release it and low side will go lower as "freon" is sucked into compressor

The system is internally "open" on the loop from compressor OUT to compressor IN, there are no "valves" that close
So not sure what you mean by "leaking" expansion valve, its suppose to pass "freon" all the time, AC on or AC off

 

he knows better than us. In all my years as a field tech i have never seen an issue that he is describing. Metering devices dont change size. Txvs can stick open but thats not gonna make both sides the same pressure either. His compressor isnt running or the reed valves are bad inside the compressor