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Discussion Starter #1
I'm so frustrated with this project. Basically, I rebuilt my system using modern components for R134 refrigerant and better performance. To cut to the chase, after borrowing a pump and gauges and vacuuming the system (it held for 24 hours), I tried charging it. However, with almost two 12oz cans of R134, the high side pressure is barely half of what it should be and the low side seems stuck around 25". The compressor comes on, it blows cool air, the low side hardline from the evaporator to the hose is freezing to the touch, the high pressure side it hot. I've now tried two sets of gauges with the same results. It's working, just not well. I simply don't have the experience to really diagnose this, and I also don't have the funds to have a shop do it. Since this is a relatively simple system I was hoping someone local would be willing to drop by and see what they think. Bad compressor? Bad expansion valve? Some other issue?
 

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At what point of the circuit are you measuring the high side pressure? Assuming the compressor is working correctly, then I would consider the possibility of blockage in one of the components or lines between the compressor and your measurement port. Did you replace the accumulator/dryer with a new one before recharging the system? Also, the condenser can become clogged if compressor had previously failed.
 

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But Mad North-Northwest
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In my experience if you keep adding gas and both sides stay low, you've got a leak somewhere that only appears under higher pressures.
 

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Discussion Starter #5
I can walk you through what I’ve done, although it’s been spread over a couple of years. With a car like this it’s sort of a fact you’ll start in a nice to have project then end up rebuilding a head or a transmission.
So the compressor is a generic rotary filled with 5 ounces or so of PAG (that’s been a while so I don’t recall, but it came with a spec sheet for the measurement). The condenser is brand new, aluminum parallel flow. I have a fan set to cycle with the compressor. The hoses and fittings are all new barrier hoses. The o-rings are new, green BUNA rings. The expansion valve is new (from a Saab but it fits). The dryer is of course new, with a new binary pressure switch. The only thing I didn’t replace was the evaporator, only because I couldn’t find one that fit without hacking up the case. I had it flushed though.
The system was totally dry and leak tested. I pulled a vacuum for about 8 hours and let it sit at -27” for more than a day, with no pressure change. Then I started charging it, and that’s where the problems began.
I can tell you the high side hose is warm, the low side cold (actually the metal fitting collects frost). The expansion valve capillary tune is attached to it and wrapped with tar tape, and the expansion valve is also wrapped. What else... after the first failed attempt I tried a different set of manifold gauges and added some R134, but it actually wouldn’t pull in more than 25” low and about 75” high. I know the compressor is doing some work because as I said the hoses have two drastically different temps and the air from the vent is cool (sort of mid 50 degree range), but the evaporator freezes up VERY fast and of course the readings on the gauges are totally off where they should be. All I can figure is the compressor has some bad seals, even though it’s off the shelf new.


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It's only a guess, but from your last description I tend to suspect the expansion valve maybe stuck open/frozen. I would back out some gas from the system. It may be overcharged.
 

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Discussion Starter #7
Well, I found a retired AC tech in my neighborhood (NextDoor finally came in useful for something) who's willing to help next weekend. He thinks it my expansion valve and has some tricks to test and maybe get it to cooperate.
 
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