A/C repair & restoration options

[jackhild59]

Originally Posted by Pete_89T2

LOL, I'm a EE, and it's been almost 30 years since I had to put up with undergrad thermodynamics, I completely forgot about the saturated vapor pressure angle... If I understand correctly, 87.5 psi static pressure would be the knee in the curve for R12 at 85*F. My static pressure was 86 psi, so it's definitely reading below that threshold, but intuitively if all the R12 leaked out, wouldn't the static pressure read zero or pretty close to it? (equalized to atmoshperic)

Glad I could help, Pete. I carried my EE major girlfriend through thermo as a freshman. Except I wasn't an Engineering student-she nearly quit school in frustration that I 'got it' and she didn't. She quit me instead, lucky break!


If that temp switch is gimp, you could have attained vacuum on the low side, but not that likely.

I would advise to charge a couple of oz of liquid refrigerant into the system then run the car until everything gets good and hot. Go back to the spray bottle and look for your leak.

Pro's use nitrogen and pressure the system up to 200psi to look for leaks.

Originally Posted by Pete_89T2

Agree with hunting for leaks, but don't think contamination is too likely since the system was never opened up, at least since I've owned the car. I suppose if the receiver/dryer was failing due to age it could cause contamination; ditto for the compressor.



Checked with the FSM, and the pressure switch is plumbed into the high side, located in the line between the condensor & receiver/dryer. It's wired in series with the thermal switch you mentioned. Both are normally closed switches, so when you switch the A/C on, the compressor will stay running (clutch engaged) as long as the pressure switch is seeing at least 2.3 kg/cm^2 (FSM #, converts to 32.7psi), AND the the temp of the evaporator thermal switch is above 38.3*F. This would explain why my compressor was running constantly - evaporator isn't getting cold enough, and the pressure on the high side was well above 32.7 psi

I recommend you replace the receiver/drier. The descant-bead retaining bag is soluble in synthetic oils. You do not want those bead spread throughout your system. Any modern (post 1996) manufactured desiccant is designed for R134a and synthetic oils.

Also,be aware that there are two different systems on the FC. One is installed in Japan and the other was installed at the port of entry. Type is not related to Sanden/Nippondenso system. If you lookup the part number at nearly ANY parts store, they always get the wrong one. Take your old part in with you to save the trip. An easy way to distinguish is the hold down bracket for the drier. If your bracket is welded on, get a replacement that is welded on. If it is clamp on, get the drier that is clamp on.

Whether you recharge w/R12 or Freeze12, use Ester oil for lube. Add a couple of oz of oil to make up for losses around the compressor seal. DO NOT use PAG in any system that has pretty much ever had mineral oil or R12 in it. Bad reaction. I don't know if you can easily even find mineral oil any more.