66 AC problems

[Gary N.]

I'm having a problem trying to recharge my 66 factory AC and wonder if anyone has ever had a similar problem. It still uses R-12 so I don't want to waste any of it. The problem I'm having is it won't hold a charge. I can pull a vacuum on it, and it will pull down a vacuum to 29-30 and hold the vacuum just fine. I have let it sit with the vacuum on it for several days and it holds fine. I even checked the high and low side ports on the compressor muffler by pulling a vacuum with each on separate since they are the only thing in the system that is bypassed when pulling the vacuum. They each held the 29-30 vacuum fine for over 24 hours. I put in a recharge and also added in UV dye. I took the car out for a 20-mile drive and the AC worked just fine. Nice and cold. I checked all the AC system under the hood with a UV light and could not find any place that showed a possible leak. The next morning, I tried the AC and I got no cold air. I looked at the dryer site glass and it showed no freon in the system. It lost the charge in under 24 hours. I once again checked all the visible areas with the UV light and saw no indication of the dye anywhere. The front of the compressor didn't indicate any leak either. I realize that the only area that I can't see is the evaporator area under the dash and it could possibly be leaking. My question is why will it hold a full vacuum and not leak at all and when it is charged, lose the freon. I would think if the evaporator was leaking it would not hold a vacuum. Has anyone ever had a similar problem?

[Harry S.]

Re: 66 AC problems

Gary, I am as puzzled as you on this. I agree if it holds vacuum it should be fine. Since it blew cold immediately and stayed cold it's probably not the hot water shutoff valve, Hot water and cold air make warm air.

I can not recall how small the r12 molecules are, but have you ever replace the Schrader valves. They will fail over time, it's just a rubber seal.

[Gary N.]

Re: 66 AC problems

Yes, I have replaced the schrader valves. I have also used a freon sniffer and they have not detected any leaks. I'm really puzzled. I also have the brass valve caps with o-rings on each of the valves.

[Harry S.]

Re: 66 AC problems

Yes, I have replaced the schrader valves. I have also used a freon sniffer and they have not detected any leaks. I'm really puzzled. I also have the brass valve caps with o-rings on each of the valves.

Good luck on the problem. Oh, I believe those brass caps should be Cad Plated.

[Mark E.]

Re: 66 AC problems

No dye visible suggests the evaporator failed during the shake down drive. Evacuate again to confirm.

[Marco H.]

Re: 66 AC problems

Gary, you may inspect the drain at the evaporator housing, to see if any evidence of dye exists there.

[Peter M.]

Re: 66 AC problems

Gary,
Try pressuring up the system with nitrogen. Most A/C repair shops should be able to do this.
Kind regards

[Gary N.]

Re: 66 AC problems

Ok another day of trying. Since the system lost all the freon overnight, I decided to pull a vacuum again to see if it would hold since someone thought that the evaporator might have failed during the shakedown. Well, the vacuum held just fine again as the other times. I had some R-12 leftover in the can from the last time, so I decided to put in enough to add some pressure to the system and leave the high and low lines connected to the ports. That way, I will bypass the low and high Schrader valves if there was a leak in one of them. That only leaves the schrader valve in the STV valve to check for a leak. I added the freon and got about 70 psi static pressure (not running) in the system and let it sit for a while and the pressure slowly started to come down. I put a little soapy water on the STV Schrader valve and got no bubbles coming from it. So, it appears that the Schrader valves are not the problem. I made sure the line connections were good and tight and they were the same connections that I used when I pulled the vacuum. The original 66 AC system uses hose fitting with clamps on the end of the hoses and not O-rings as seals. I checked all the hoses for ware and made sure that the clamps were all tight. Also rechecked the fittings and hoses for UV glow and found none. At this point I have found no UV leaks under the hood including the front of the compressor. I also checked the evaporator water drain area for any UV glow and saw none. I can only surmise that the evaporator O-rings could leak under pressure and not under vacuum as a possible problem since I have no way to see or check them. Looks like I may just have to live with the Texas heat since I'm not ready to tear out the evaporator area at this time. If any of you can come up with any other ideas, I'm certainly open to hearing them. Thanks for reading this.

[Gary B.]

[Gary N.]

Re: 66 AC problems

I agree, plus a vacuum is pulling everything inward and may seal that way, where adding freon to get a 70-psi charge or more is pushing out. My problem right now is finding the leak. I've used both a freon leak tester and UV dye so far to no avail at least in the engine compartment. The only thing that seems to be left is in the evaporator area inside the car.

[Timothy B.]

Re: 66 AC problems

I don't know much about A/C but can you put air pressure in the system and listen in the vents for a leak in the evaporator.

[Domenic T.]

Re: 66 AC problems

I don't know much about A/C but can you put air pressure in the system and listen in the vents for a leak in the evaporator.

Tim,
That's a good idea. I made a gage that attaches to the system and pressurized all but the compressor which I do seperatly with nitrogen @ 340 PSI. I actually pressurize the system with about 100 lbs of propane and use a sniffer. As someone pointed out, vacuum can actually seal some parts , especially rubber O-rings. Air moisture can be removed (as pointed out) by pulling vacuum. Not rocket science.

Dom

[Joseph S.]

Re: 66 AC problems

I would have to reiterate a point Gary made. I worked on my AC system on my 66 for quite some time with the help of some of the guys on this thread. Among other issues I was not able to effectively identify leaks until I acquired a refrigerant leak tester. They are not expensive at all and there is quite a selection on amazon. I highly recommend them along with NOT over tightening 'O' ring fittings.