Greetings all,

I'm about to redo my 84's AC system and have a few questions. I'm starting w/a system converted to R-134a by a PO and it holds pressure. However the reman compressor is noisy and the system only gets slightly cool but not cold. I have no idea how much oil, sealer, dye, etc is in the system, but there is some of each. I currently have a new gauge set and vacuum pump and a new AC Delco compressor and accumulator on order. I also have a new orifice tube.

My plan is as follows. Any comments would be most welcome.

1) Evacuate the system.
2) Open system and remove accumulator, orifice tube and compressor.
3) Back and forward flush evaporator, condenser and hoses w/mineral spirits and dry compressed air.
3) Replace compressor, orifice tube, accumulator and seals/o-rings.
4) Vacuum system and replace w/PAG 150 oil and straight R-134a w/no additives. (sealers or dyes)

The FSM indicates to add 6 ounces of oil to the compressor. Then it indicates 3 ounces is usually retained in the evaporator, 1 ounce in the condenser and 2 ounces in the accumulator, of course all based upon using R12. My question(s) is do I really need 12 ounces of oil in the system or am I misunderstanding what it is saying? This seems a bit much based upon other info I've read online. And beyond pouring 6 ounces of oil directly into the compressor before installation, do I also need to add oil to each component before assembly or can I just use a pressurized oil charge can to do the rest? And again, how much is "the rest"?

Lastly I've read to use only approx 80% of the R12 amount when using R-134a. R12 specified amount is 36 ounces so 28-29 ounces of R-134a seems about right. I presume that this 28-29 ounce number is R-134a only and does not include whatever amount of oil has been added? Is that correct? I've also read where I need to see 1.8 to 2.2 times the pressure on the high side as the ambient temp in front of the condenser. Is this correct and anyone know a more specific number for this system? Also approx what low side pressure will/should I be seeing?

Thanks in advance!

 

I would replace the condensor - they're cheap and difficult to flush.

Never seen a 12 oz oil capacity. Double check and make sure it's not 8.

Most of the oil is going to be in the Accumulator. I like to split whatever I'm adding between it and the compressor and since you appear to be doing a complete rebuild, I'd put half in the Accumulator and half in the compressor. Compressor should be flushed before you install it too. Drain out whatever was put in it by the reman or manufacturer. Add 4 ozs of whatever you're going to use. Spin a dozen or so times in one direction - then the other - drain and repeat and then add fresh before you install.

To me, Brake Parts Cleaner is easier to use. Remove the lines and spray it through them. For the Evaporator, Put a white cloth over one end and keep spraying until it comes out clean.

The 2.2 times air temp at the condensor works. Bottom feeders like the Vette can be 10 degrees higher at the condensor then the outside air temp. 80% of the R12 charge is a good starting point. What you want is about 25 to 28 psi on the low with an outside temp of 70 to 80 degrees. Check all pressures with the engine cranking at 1200 to 1500 rpms, main fan running, a/c on max. The real problem with these conversions is that the fan comes on a little later than what might be ideal for high side control. Nothing you can do about it since it's a switch and no one that I know of makes one that will open or send a signal at a lower high side pressure. This means you'll probably get better results while charging then in the real world.

When done, check cutoff threshold by pulling the blower motor connector and note the low side when the compressor cuts out. You'll want 22.5 psi for R134. Lower by turning the screw between the Low Pressure Switch contacts counterclockwise; raise it by turning it the other way.

 

I know I probably should change it. But frankly the 84 is "just" the driver and I really don't want to drop another $200+ into this project. I just want to get the AC "refurb" finished so I can get back to the other money pit, the 75 C3. So based upon this, any other comments on how best to flush out what I can? I've also read about installing filters and screens to help protect the new compressor from any old junk left in the system. Any thoughts on this?

I've re-read the fsm now several times and while not completely clear, I'm guessing it's trying to indicate for example if you replace just the evaporator, their estimate is that it will have retained approx 3 ounces of oil so you should add this amount back to the system. However in this case I suppose it matters little to me as with a fresh cleaning I will be starting from scratch. So 8 ounces it is.

Compressor is a new AC Delco and I was going to drain and add fresh oil. However thanks for the tip on flushing the compressor. I would have likely missed that step.

OK, brake cleaner it is. This probably has a higher flash point than mineral spirits too so it should evaporate a bit better also. Thanks!

Is this the switch on the back of the compressor? If so perhaps different pressure values are available for some other industrial application? It seems to be a common threaded fitting. I believe I've even seen adjustable pressure switches somewhere too. If something else could be found what high side pressure would you want it to switch off at? And do you know what pressure the current one switches at?

OK, will do.

Thanks so much for your input. It is much appreciated.

 

Fan switch for your Year is on the back of the compressor and a schematic in your Manual should give it's parameters. Most R12's come on (open) at around 220 psi and then close at 190 psi. The goal is an average head pressure of 200 psi. You want about the same for R134, but it's increased density can have it building pressure much faster, overwhelming a system that doesn't start the fan until 220 psi. If available, dropping that on signal to something below 200 would probably work a lot better (finding something is the problem). Most just reduce the charge and the one thing you want to do is make sure that the high side never gets up around 300 (easy to do if it's a 100 degrees). It'll overheat and all you'll get is 60 degree air out of the vents. If you want you can stick with R12. Get your license online at www.epatest.com or any of the sites at www.epa.gov or on the forum at www.ackits.com (which also has plenty of info to help you out), then buy to your hearts content.