A/C help please!

[foamypirate]

Originally Posted by Low Elco

I know NOTHING about AC stuff. AT ALL. Got an 87 SWB C-10 with factory ac that I got with none of the engine related A/c stuff. I've bought a receiver, orifice tube, compressor, compressor hoses. I yarded all the compressor brackets. Turned out the condensor was broken, so I got one of those. It's a completely different design optimized for 134, and had some fitment issues, which are apparently a common complaint. I got that in, got the brackets on the compressor, and saw a sticker that says the compressor is pre oiled and that I need to put "x" ounces of oil in. What oil? You're supposed to scan the QR code on the sticker to find out, but that just takes you to a chart of all makes and models where I think they're saying they put mineral oil in. Now, If I'm right, you can't have mineral oil in a 134 system, and you can't get 12. So now what do I do? Also I just saw a video where I guess there's a high side switch in the compressor? I don't have that or any wiring for it. Where does the orifice tube go? Anyway, If anyone can help, let me know. I've been wrenching for a long time, but I know nothing about this.

Thanks, Chip

Since you are starting with a basically a brand new system, you can start with factory specs for oil. My 87' manual specs 10oz of oil for the system.

Since you are converting to R134a (I presume...), ditch the oil in the new compressor. This way you aren't guessing at the amount of oil in the system (who knows how much oil Bob put into the compressor during manufacturing...) Turn it over, and drain out as much as possible. Be sure to turn over the compressor while doing so (make sure you actually turn the shaft, not just the clutch).

Go ahead and flush the evaporator with some A/C flush solvent or non-chlorinated brake clean, and make sure you get it completely dry.

Add the oil back to the system. The R4 should use PAG100 at a minimum, but PAG150 is even better. I like oil with UV dye in it, for future leak detection. Put a couple of ounces everywhere. I like 3-4oz in the accumulator (which is different from a receiver/drier. Squarebodies all had accumulators; there is a difference). 1-2oz in the suction hose (big hose). 2-3oz in the compressor, spin the shaft around a few times (15 in each direction would be good). 1-2oz in the condenser inlet. Just make sure you get the 10oz into the system.

The accumulator should be the last thing installed, since it contains a dessicant. If you open it up, it will start absorbing moisture.

The orifice tube goes into the small tube on the bottom of the evaporator, SHORT SIDE TOWARDS EVAPORATOR. The long side should be facing towards the small liquid line coming from the condenser. It should go all the way into the tube to where you can just barely see the tab, slightly recessed into the tube.

I would recommend new hoses, if possible. Any good A/C shop should be able to braze a fitting into the hard line on the high side for a high pressure cut off switch (HPCO). The compressor discharge line, before the condenser, is optimal placement, since the system will shutdown if the condenser gets blocked up. If you put it after the condenser, and the condenser plugs up, creating high pressure at the compressor, the HPCO would not trip, since it's upstream of the blockage. The HPCO should be wired in series with the low pressure switch.

Use refrigerant oil or Nylog (Nylog is polymerized refrigerant oil) to coat all your o-rings and threads. This helps prevent damage to the o-rings during tightening and helps get a good seal.

Once everything is all buttoned up and put together, you can have the system vacuumed to boil off any remaining moisture and verify the system holds a vacuum (indicating no leaks). It can then be charged. A lot of places prefer to start at 80% of the R12 charge, but I prefer to start lower, having experienced a shop overcharging my conversion right off the bat with the 80% number.

Hope that gives you a good start. Let me know if you have any more questions. I just recently went through all of this myself. Once I got my refrigerant charge correct (the shop I originally went to overcharged it), I'm getting pretty decent performance for an old system with the evap in the engine bay. I've seen down to 42* at the vent outlet in 95F heat. Full blast in 100F - 70% humidity was hitting 48*.