Hi,

I bought a 1977 Ford truck a couple of years ago. It has factory air, but the compressor was removed and the hoses were capped and/or poorly taped off when I bought the truck.

I got the bright idea, I'd try to get the air going, but I didn't know anything about a/c systems. I bought a York type (same as what it would have had originally) compressor from Autozone. They told me it was for r134. I put it on the truck along with a new filter/dryer and new expansion valve.

I took the truck to the local shade tree mechanic and he stuck a el cheapo vacuum pump on it for a little while and threw some oil and two or three cans of r134 in it.

Well... since then, two summers have passed and it has never worked right.

The compressor really vibrates at low rpms. The air is just barely cool enough to tease me into thinking I have air conditioning. I know this sounds odd, but it seems to work best after I've sat at a stop sign and then take off. It's like idling the engine allows it to "catch up to itself" and then when I drive about 30 mph after a stop sign it actually blows pretty cool for a couple of minutes. But at highway speeds it isn't cool at all. This seems to be the opposite of what I've read. I had the heater & a/c box all apart changing the heater core and all the doors and seals are in good shape inside it. I don't think I'm getting outside air in. At least not in any quantity.

Last summer a friend tried to help me, he had one of those cheap gauges and he tried to put some r134 in it but it didn't accept much at all; and it didn't help.

I've had about as much as I can take. I need some air conditioning. Should I try to flush out the system, install a new filter/dryer, and get a fresh charge of r12? I'm concerned about trying that because the kid at Autozone told me the compressor was for r134.

I'm pretty confident I don't have any leaks in the system.

Please help me out,
Thanks,
John Thomas
jntmjt1@sbcglobal.net

 

I did an air conditioning install on my 1970 F100 a while back. I had it working, but it never did work quite right. I could never find the correct charge amount of R134a. Also, the compressor made some weird noises with the Ester 100 oil that R134a uses. It's my opinion that those York compressors were made for mineral oil, R12, and nothing else.

Anyway, I noticed the exact same symptoms you've got! It would get cold driving through town, then die on the highway. I think I almost had it tracked down, but by that time it was fall and I quit messing with it. I believe it was something about the system controls that were designed for R12 not working with R134a.

If you can flush the system and get R12, that would definately be the way to go. Be prepared to pay though.

 

The compressor doesn't care what refrigerant is in there, it's just a pump. The only difference for compatibility purposes is the composition of the seals. They must be compatible with the different lubricants required for each refrigerant class.

Other than the seals, the major differences between an R12 and an R134a system are the condensor size and the expansion device used. A condensor for an R134a system must be a little larger in order to reject sufficient heat to work as well as the original R12. The expanion device, typically an orivice tube in the CCOT systems, sometimes will work better if the orifice size is adjusted. Usually, a blue or red tube is the better choice.

Without guage readings, it's pretty tough to offer an informed opinion as to why these systems are not performing very well.

Steve

 

I've got a 77 F100 with no compressor in place. All other parts are there and I want to get the AC going in this guy. I live in MS and it's very necessary here.... Have any of you had luck resolving these issues with the R134a conversion?

So far I think I need (at minimum):
new o-rings
R134a conversion fittings
expansion valve
dryer
10 oz ester oil for compressor

 

The best advice I can give is to take your vehicle to a shop with the expertise and equipment to check the system for leaks, fix the leaks, evacuate the system and then charge it properly. If the system was not vacuumed properly, it could still contain air and moisture and will never cool well. As already stated, r12 converted systems do have a problem with the condensor being a little on the small side for 134a. This mean that the pressures will run higher and the higher the pressure, the warmer the air coming out the vents.