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Back to R12?

wildrideperformance on Sun September 16, 2007 7:25 PM User is offline

Year: 1969
Make: Chevrolet
Model: Camaro
Engine Size: 350
Refrigerant Type: HC
Ambient Temp: 92F
Pressure Low: 75psi
Pressure High: 75-80psi
Country of Origin: United States

This is my first post to this forum, but it has been an excellent resource for my A/C education. I am an A/C novice, but I am pretty mechanically inclined and have been playing with every other aspect of cars for many years. Right now, I'm at my wits end!!!

Here is my situation. My 69 Camaro factory A/C has been inoperative since 1987, and I decided to bring it back to life this summer. I replaced the compressor (rebuilt A-6), hoses (reproduction barrier), condenser, drier, and txv. The compressor and txv were sitting on the shelf for 20 years or so, but never used. I did research on refrigerants, and decided to use Enviro-Safe (HC blend) after doing the required R-134a retrofit (fittings). I wanted to go back w/R-12, but as a do-it-yourselfer and with the price of R12 (and falling for the utopian description of EnviroSafe) I bought a case on e-Bay. I flushed and pressure tested the evaporator. Even though the condenser was new, I flushed that too. I replaced all o-rings, added 11oz of FJC DyEstercool oil (6oz in compressor after draining mineral oil , 3 oz in evaporator, 1 oz in condenser, 1 oz in dryer), vacuum tested (held 25" vacuum overnight), and vacuumed for 2+ hours. I then charged per their instructions (can upside down, as liquid) - I got as much as I could into the system, which brought low/high side up to ~70psi. I started the car and fired up the A/C, and almost immediately the POA valve / low side return froze up back to the compressor. The low side reading was ~70-80, while the high side was only slightly higher. The A/C belt was not slipping. The compressor was not making noise. The vent temps were high - no cooling (105F). At first I though that the issue was that the system was undercharged, so I kept adding refrigerant, but the low only went up with more refrigerant.

My first thought after doing research was that the compressor was not up to task I bought a rebuilt (Murray) A-6 and installed that. Recharged w/Enviro-Safe - same result - POA froze back to the compressor; evaporator outlet is hot; evap inlet/txv not hot; pressures basically equalized in the 70-80 psi range.

Next, I thought that perhaps the txv was bad (stuck open). This was before I did more research and realized that the txv does not regulate pressure in the evaporator - this is the POA's job. Needless to say, I had the same result as before - frozen POA, pressures same.

Although I had tested my POA per the instructions on this site and it appeared to pass, I bought a used (tested) POA from a guy on ebay and installed that today. After reassembling, pulling a vacuum for 3 hours, and beginning my re-charge, the same thing happened - POA is howling (wide open, I assume) and freezing back to compressor, and pressures are in the 70 range both low and high.

I don't normally use the 'throw new parts at it until it works' approach, but that's pretty much what I have done here, although in somewhat of a logical manner. I think that the original compressor and txv that I replaced are fine. My original POA is probably good too.

In my mind, I have narrowed the problem down to a couple of possible things:

1. Refrigerant. Now that I'm knee deep in this project and have done a lot more research on this forum, I realize that EnviroSafe is a blend. Perhaps the cans I got were not filled properly or I am not getting the proper ratio when I'm charging. Just a guess here. Like I said, I'm throwing darts at this point. I have not heard of this being an issue with anyone else unless they have a leaky system.

2. Restriction of some sort in high side between compressor and the drier. The high side gauge fitting is between the drier and the txv, and like I said above the pressure is basically equalized between the low and high side fittings (low side is on POA). As I said before, the condenser is new, and I flushed/blew it out. The hoses are new. The drier is new, but it had a manufacture date of 1998, so it had been on the shelf for a while. I would be more inclined to believe that this was a possibility if I could feel the condenser and high side hoses prior to the drier heating up due to extreme pressure caused by a restriction, but they are barely warm to the touch.

I'm pulling out the hair that I have left. Regardless of what the issue is, based on what I have learned, I want to go back to good old R-12, but given its cost I don't want to do that until I am sure that I have fixed my root problem(s).

Thanks in advance for your help and advise.

Dougflas on Sun September 16, 2007 8:01 PM User is offline

To begin, 25 inches of vacuum is not enough. Make sure your gages are zero'ed before you begin. I only use R12 and R134. POA systems can work on R134 with some adjustments. A low charge will make POA valves frost over. First, make a decision...R12 or R134. In my opinion, forget about the blends. If you ever get a leak, you'll reaaly need to do a complete recharge because of the glide of the refrigerant. To test a TXV off the vehicle, blow thru it with the sensing bulb in your hand. You should be able to blow thru it. Next, place the bulb in ice water. It should shut and you can't blow thru it. If you tested the POA as per the instructions on this forum, set it for 26 lbs for r134 or 30 lbs for r12. Make sure the sensing bulbis placed correctly on the evap tube and insulated. For r134, start with 80 to 85% of the factory r12 capacity. Run engine at 1200 to 1500 rpm, blower on high speed, and place a 20inch window fan in front of the vehicle.

mk378 on Sun September 16, 2007 8:15 PM User is offline

People have used R134a successfully in these. I would suggest getting rid of the HC (deep vacuum) and trying R134a first, and report what that does for some further advice from people with experience on these systems. Be sure that the "ester" oil you have installed is intended for R134a. If you leave the POA calibrated for R12, it will still work but won't get quite as cold.

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