Shagg

Ok so I have 2 different trucks with ac ill be working on. Both of them have factory a/c. First is a 1990 4.9l that has run out of refrigerant, I have the adapters to put 134a into it, but I know that there is a lot more work that has to be done before I can just fill it up, I know that it needs to be completely evacuated, and then I believe that the oil will have to be replaced, so if anybody has done this before, Id like some advice.
The second one if for my '89 4.9l, When the a/c went out, rather than figuring out what was wrong, all of the lines, and the compressor were just removed from the truck. I still have the compressor, but it has been sitting in my garage for a few years. The condenser, accumulator, and evaporator core were all damaged when my truck got hit, so ill be replacing those. I just want to know if I can do some kind of test to make sure the old compressor works, and also what I would have to do to get it ready to use, since it has been sitting for a while and is dirty. The pulley does freely spin, but I dont know if that means anything.

wde3477

Converted my '89 some 20 years ago, so drawing from memory and the wisdom of that time - changed all O-rings from the OEM 'black' ones to the recommended 'green' ones, replaced the receiver/drier, drained the oil from the compressor, ran a refrigerant flush through everything, refilled with the recommended amount of R134 compatible oil, installed and wired in a high-pressure cut-out switch in series with the existing low-pressure cut-out, adjusted the low-pressure switch for a lower pressure (IIRC, about 1/8-turn CCW on the screw found when the device was unscrewed from its low-pressure port) looking for a cut-out at about 22psi rather than the original 28psi. Installed the R134 port adapters as well as the kit to upgrade my gauge manifold with the same adapters as well as the dial gauges that had the R134 scalings. Pulled a vacuum and held to check for any major leaks. Refilled with about the recommended 80% of the spec'd weight of refrigerant. Advice given was that the R-134 may leak or seep a bit through the old hoses, whether it be that or other leak or just being ~10 years old at the time, ended up putting about 1/2 can in per year. Cooling wasn't as cold as with the R-12 but tolerable, generally running the fan 1 notch higher speed kept things comfortable but nowhere near the previous ice-station zebra cold. Whether I followed bad advice, right or wrong, this is what I recall going through. Still totally worth it given our high humidities along with summer temps in this area. Looking back, probably would punt changing out the O-rings and the high-pressure switch install.

Nothing much to offer on your compressor with the other truck, other than if the ports weren't plugged/taped off - the internals being exposed to air for an extended period won't do it any favors, so a decision between giving it a whirl at the risk of a do-over, or just replacing it from the get-go.

Hope this helps.

Slowbrick

Shagg,
There is a difference in doing just enough to the A/C to make some cool air and doing the conversion correctly. When I converted my '92 to R134a I used all new parts in the system; new hoses, new evaporator, new condensor, and, even though I had a couple of used compressors in the garage, a brand new Motorcraft compressor. All of these parts were designed for a '94 truck that used R134a. It cools excellently and has been trouble & leak free since the conversion.

To just add the adapters and change the o-rings to the R134a style may not get the desired cooling results. It works OK for some people. IMO, if not changing all of the parts on your whole A/C system you would be better off sourcing a few cans of R12 and staying with that refrigerant than doing a conversion. It's fairly easy to find R12 on Ebay or garage sales. It doesn't cost all that much either.

Good luck,
Jonathan

Steve83

If you have to buy a bunch of replacement parts, either buy enough to convert to the factory R134a system ('94-96 parts), or just buy a complete factory '94-96 R134a system at the JY and drop it in (my preference because it doesn't require any evac/flush/recharge).


(phone app link)

The differences include:

• evaporator/outside HVAC box shape
• condenser type
• hood latch support
• liquid line (condenser to evaporator)
• flush old mineral oil & switch to PAG46

There are a few other differences, like the threads on the accumulator for the low-pressure switch; but the workaround is to adjust the original (white) pressure switch to the new pressure setting. A high-pressure switch (and its simple wiring mod) is required by law, but since no one inspects for it, and since high pressure usually grenades the compressor anyway, its necessity is arguable. The rubber flap behind the bumper is more-important with R134a, and there are additional flaps beside the condenser that should be added.

The captions in this album (& the links in them) give more detail:


(phone app link)