Automotive Air Conditioning Information Forum

Hello,
I am unsure what to try next. I'm working on an 80's mustang with the orifice/ accumulator type AC system. I currently have all new lines (3) on it, new condenser, evaporator and compressor. I put around 8 oz. of PAG oil in between the compressor and lines. I vacuumed it down to about 30" and it held for hours. I added about 2 cans of 134A and initially I had a very high (like 350 psi) high side. Now I can't remember if my electric fans were on at that moment because it's possible engine temp wasn't high enough and I know I need to address that to have them on when AC is powered. So it's possible I didn't have any airflow across the condenser at that moment. Anyway the pressures leveled out to around 274/38 at an ambient of 93 with a temp drop of about 27-28 degrees below ambient. The next day it wouldn't blow cold, started cycling, high side went between 150 to 200. I suspect maybe my conversion fittings leaked, but I think I have a blockage because when down it held around 100-120 high side and only 5-10 low side. I thought they should be equal? Prior to replacing compressor and evaporator it wouldn't hold vacuum for more than a few minutes, I made the mistake of using compressor air to see if it would hold that. So when I replaced evap & compressor I also replaced the accumulator again. So I thought maybe that dirty air clogged the orifice but when I replaced the liquid line for the second time I didn't see that and there was pressure trapped in the liquid line even after the system was empty. Sorry for the long post but I'm stumped. Thank you

Is this a 1989 Mustang?

Several thoughts come to mind if this is indeed an '89:
—You mentioned that you added 8 fluid ounces of oil between the compressor and lines, which is unusual. If I understand correctly, you might have forced the compressor to compress liquid oil on first start-up ("slugging"), ruining the compressor.
—You also mentioned that you added two cans of refrigerant (12 ounces net weight each, without any sealer or other additives??). According to the specs I have for that model year, the system takes 40 ounces of R-12. Chances are, the R-134a capacity would be close to that amount. In any case, I think you have a ways to go for a full charge.
If you were concerned about the high high-side pressure while adding refrigerant, first make sure that the fans in front are roaring while charging. If not, then add a temporary, strong auxiliary fan blowing through the condenser from the front to reduce the HS pressure to an acceptable level. At a 93°F ambient, you should be seeing HS pressures around 210-220 PSI, and LS pressures around 28-30 PSI.
—If they aren't working right, investigate the existing fans to determine why they aren't working up to snuff (not coming on at all, weak, etc.).
—The static pressures should be roughly equal after about a half-hour. The HS seems normal at that ambient, but you're seeing only 5-10 PSI on the low side, which suggests either your Manifold Gauge Set (MGS) isn't hooked up correctly, or a partially plugged metering device—in this instance, the Orifice Tube (OT). Is the OT removable from the liquid line, or is it one that's crimped into the line itself, requiring that the entire line be replaced?
—I don't think shop air would cause a restriction if you have some kind of filter and desiccant dryer on the line.
—If it's an 1982 to 1988 model year Mustang, you'll have to refer to the under-hood decal for the proper R-12 refrigerant and oil specifications.
—The pressure trapped in the liquid line is a mystery, unless your MGS isn't connected correctly.

Thanks so much for the response.

So it's an 82 year, The under hood sticker say's 2lb 10 oz. I believe.

I read varying specs for oil capacity, from 6-8 to 8-10. So I drained the oil that came in the new compressor while also hand cranking it because it didn't look like the PAG I had and wasn't sure what it was. I then added about 6 oz to the compressor and another 1-2 to the lines. I hope I didn't ruin it but how are you supposed to add it? I thought that high 350 high side coudl have been because the fans weren't on?

Regular 12 oz cans of R134A, no sealers or additives.

I understand now what I did not having the fans running and will address that with the fan controller and make sure they are running next time I try charging it.

The orifice is supposed to be inside the liquid line.

I did NOT have a filter or dryer on the compressor, that's what I was worried about.

The manifold gauges were hooked up correctly. red high side to the fitting on the line between the compressor and condenser and blue low side on the fitting on the compressor that connects to the line with the accumulator that connects to the evap.

When I first had the unequal pressures while down I suspected maybe my low side gauge was faulty so I opened both manifold knobs to allow the static high side pressure to come over to the low side gauge and it read exactly what the high side gauge was reading.