I took my AC compressor off to drain the oil but it was gone

[1$Chuck]

The back story:
This is a 90 truck, I have no idea how long its been since the AC worked. There was a teenie tiny bit of charge left in it, that I could only tell by pushing in the schrader valve to hear the hiss, it wouldn't registrar on my gauges. The compressor spins freely and doesn't make any noise (I jumper-ed it to make the clutch kick in and run a while back just to make sure it would run OK).

I'm working on doing a R12 to R134a conversion so I wanted to drain the old R12 oil out of the system. I did pull a vacuum on the system before I opened anything up just so I had some piece of mind that I didn't have a leak somewhere before I started. After seeing the system hold vacuum for a couple hours, I pulled my compressor off last night and turned it upside down and I don't even think I got a teaspoon of oil out of it. I left it sit upside down all night and I still didn't get anymore oil out if it. I also pulled my receiver dryer off (going to replace it) and it was also oil free.

So where did my oil go? Did it vaporize and slowly leave with the R12 over several years? I'm pretty positive this system hasn't ever been monkeyed with. Would you trust that compressor enough to put it back in?

[ellis93]

I'd trust it. If I was flushing the whole system then I would dump 8oz of oil,with the bright green dye in it,in the compresser and re install.
Its a common occurrence for oil to escape with the freon. Think about how the connections are sealed at the dryer and condenser,with embossed metal gaskets. I've never had mine hold a proper charge longer than a couple of years. It doesn't take very much to top off, maybe about 6 to 8oz out of the 12oz can.

Oh if your old oil looks like there is metal in it, I retract my statement and you should get another compresser. After thought

[1$Chuck]

Are you talking PAG oil, or ester oil?

[ellis93]

I use Pag oil,usually its the 100 or 150. I believe its better but that is opinion not fact. If your gonna flush the system then I'd swap it in. If your not then use the ester oil. It can be found with the dye in it as well.
Something else I find worth mentioning is the different dyes that can be bought. Green is the best to buy cause its easier to spot, the red stuff tends to blend in to its surroundings.

[1$Chuck]

Thanks.

One more question. I'm going to go ahead and replace the expansion valve while I'm at it because its old and I don't know anything about it. I was looking into the low pressure switch that threads into that and I believe that if I were to have to replace that switch, I would loose my charge. Is that correct? If thats true then I'll just go ahead and replace it too. Should a guy use some thread sealant on those threads? Just standard pipe dope or is there something special for AC?

[ellis93]

The replacement of the expansion valve is a good idea. They tend to stick or not let the needle inside travel as freely. As far as the switch and its replacement I don't know. I'd roll the dice on it for the shear fact that aftermarket parts( electrical parts) tend to suck. Mine been in the same truck since 93.

When I replaced my expansion valve I used regular old teflon tape. Seems to work for me, with no sign of a leak around it.

[1$Chuck]

I pulled off my expansion valve last night and I'm glad I did there's some crusty looking crap in there. The new expansion valve has the tapped hole for the pressure switch on the other side, I read somewhere that the newer ones are like that and you've got to modify your wiring to get it back on there which is a real disappointment.

[Diesel]

The new valves won't fit as the switch wiring hits the blower motor housing. I just cleaned up my valve with pb blasterband reinstalled.

[ellis93]

The new valves won't fit as the switch wiring hits the blower motor housing. I just cleaned up my valve with pb blasterband reinstalled.

Did you do the 1/2" out thing with the sensor?
What brand of valve did you buy?

I've had an aftermarket Murry brand on mine and it fit alittle close, but it fit. The Mopar part I have now is the same way.

[Diesel]

Yeah I pulled the temperature probe out a hair. The expansion valve wouldnt fit in any way shape or form. Mine was from Advance Auto - I believe four seasons. How much for a new Mopar unit?

[ellis93]

I gave 65 for it 4 or 5 years ago. I'm not really sure on the time frame but I remember what it cost me.

[1$Chuck]

The new valves won't fit as the switch wiring hits the blower motor housing. I just cleaned up my valve with pb blasterband reinstalled.

I managed to get mine in there, but i had to make up some 90 degree terminals for the wiring