1990 NA 240 AC inop

I recently picked up a clean, low mileage 240 and I'm in the process of shining it up, and making everything work. The latest project has been the AC, but it's been a struggle. I had some minor success with it earlier in the week. At one point, charged with r134-a, it worked somewhat poorly for a short time. After some reading I'm wanting to use air duster, but right now everything is screwed up. I've changed the compressor oil, receiver/drier, and added R-134a fittings. The weather here is mid 90s with 95%+ humidity every day.

Currently:

I had everything evacuated, it seems to hold pressure well, pulled a vacuum for about an hour, then let it sit. After I kill the vacuum pump it slowly creeps up to ~18psi vacuum, but then holds there indefinitely.

When I charge the system the compressor kicks on, and then never shuts off. I added the appropriate amount of refrigerant and my low side has almost no pressure, the high side is at 130lbs all the time. At rest they both equalize at ~90lbs. I've tried undercharging, overcharging, air duster, R-134a, no difference. Hot ass air out the dash.

When it's charged the the proper pressure the thermal expansion valve before the evaporator is very cold, and covered in condensation, but the evaporator is warm. I'm sure this is some of my problem, but my pressures aren't really indicating that. (unless they are, I'm pretty new at this).

Anybody have any ideas? Maybe there's an AC guru in here? If I left anything important out let me know, and I'll get you some info.

Thanks!

Have you checked the orifice tube to make sure it isn't clogged and is also installed in the right direction? When I replaced the ac compressor on my 740, I also replaced the reciever driver and oriface tube. I charged up the system and it worked poorly. Turned out that the orifice tube was installed backwards. I also replaced my condenser as well.

dartheyeball said:

Have you checked the orifice tube to make sure it isn't clogged and is also installed in the right direction? When I replaced the ac compressor on my 740, I also replaced the reciever driver and oriface tube. I charged up the system and it worked poorly. Turned out that the orifice tube was installed backwards. I also replaced my condenser as well.

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This system uses a thermal expansion valve instead of an orifice tube. I'm suspecting it's blocked up for sure.

I had the expansion valve clog on an 84 turbo I used to have. A shop cleared it with their machine. Worked great after clearing the blockage and a fresh batch of R12.

dl242gt said:

I had the expansion valve clog on an 84 turbo I used to have. A shop cleared it with their machine. Worked great after clearing the blockage and a fresh batch of R12.

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I wish R12 were still available easily. I even have some at my old shop, but that's 1800 miles away. Air duster supposedly behaves much like R12, so hopefully once I get stuff straightened out it'll work just fine. I've got a leak somewhere now, so it's time to find that.

I tried air duster on my own car. I did not get much cooling out of it. you can find R12 on craigslist. Myself I like duracool. Its super hot here in the ozarks and im getting 38 degrees at stop lights. I have original equipment except dryer and expansion valve. I have the exp. valve set at 3 turns out.

original dryer bag could of broke and put beads in your system which wold plug you expansion valve. I know happened to me once. Where are you located.

90volvo said:

original dryer bag could of broke and put beads in your system which wold plug you expansion valve. I know happened to me once. Where are you located.

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This happened to my 90.

I'm in South Texas, it's hot as balls all the time. I put a new receiver drier in it already as part of the "retrofit". Now that it's empty again I'm gonna take a look at the expansion valve setting, change some o-rings, and order some duracool. It was my next choice after the air duster. I had it working on R134-a, but not well.

I'm in Houston. I installed a newer universal parallel condenser in mine as the old one had a hole and it does pretty well with the duracool.

I'm bumping this up because I have some new problems related to the HVAC system. I had the AC working pretty well, but the TXV got gummed up and caused a lot of grief. I just have some questions.

1. Where does the AC thermostat probe go?
Currently I have it inside the evaporator box attached and insulated to the discharge line of the compressor.

2. What is causing just the passenger side vents to blow hot air off idle?
I installed a new "old style" heater control valve, I've adjusted it a few times, but I still get hot coolant in the heater core. I'm suspecting an upgrade is in order?

Thanks!