'69 A/C Help Needed

Hello All, I am trying to get the A/C working on my car. It’s a stock system, someone has done some work on it in the past; new condenser, receiver/dryer, and low pressure line. Yesterday I changed all of the o-rings in the system, vacuumed it- ran my electric vacuum pump for 45 mins; it pulled 27 inches of vacuum and held it for 40 mins so I charged it with some R12.

When first charging I only had the low side of my gauges hooked up. It started to get cold then the compressor started making some noise so I shut it off and added some oil to get it up to factory level spec. I then hooked up both the low and high side gauges and proceeded to finish charging. I noticed that the high side pressure was at 250 at idle, but if I sped the engine up to around 1500 the high side would climb quickly to 400 and I unplugged the clutch wire to shut off the compressor. I noticed a couple of times that when I engaged the compressor that the rubber hose coming off of the discharge side of the compressor would jump around and smack the inside of the engine compartment side wall.

I’m also only getting a very little amount of air flow out of the center vents, but think I have a vacuum line or vacuum line problem under the dash, but will deal with that later once I get the system running properly.

The low side seemed normal running around 20-30 psi. Anyone know what could be the cause of this or what I need to look at?

Possibly a plugged orifice tube or evaporator coil?

I was thinking something plugged or a problem in the compressor maybe also. Do these systems use an orfice tube? I thought they used an expansion valve, which I’ve also wondered if that could the problem.

Stock is an expansion valve. I need a refresher on A/C myself, but I wonder if the valve is not opening when it gets very cold if that could promote excess high side pressure. Thinking outloud here: Or, do you think it’s possible you overfilled the charge?-----but then the lowside might read high too. Is it possible the moisture entered the system? Environmental conditions like high humidity can cause pressure readings to be askew. Although I don’t know which way it sways them.
I’m working on a/c too—but I am only at the stage of evaporator box repair.

No problem, I didn’t know what the expansion valve was until I looked it up in the factory manual and my a/c book so I’m right there with you! I was also wondering if I overfilled the system, but it didn’t seem like I put much in; I kept opening and closing the low side valve on my gauges checking the low side pressure in an effort not to overcharge and I agree with you, if it was overcharged the low side would be high also. My a/c manual did say moisture in the system could be the cause, but I pulled a -27psi vacuum on it for 45 mins and it held this reading for 40 mins before charging so I’m thinking/hoping there isn’t any moisture in the system. I do know environmental conditions can cause different readings like you said, but when I charged the system it was about 9pm, around 80 degrees, not sure of humidity, but felt average fro my area.

Uggh, I feel for you doing evaporator box work, that is my biggest fear and hopefully something I don’t have to do.

Thanks for the thoughts and if you can think of anything else let me know.

Some thoughts:
Are you using the correct oil for R12? Should be mineral oil (NAPA). The oil for R134 is different and doesn’t react well with R12.

If the expansion valve had been opened for years to engine compartment heat, dirt, etc. then it’s a good chance its gummed up and won’t fully open or close. I’ve heard of soaking it with carb cleaner to loosen it up, but it would be easier to buy a new one.

About 3 lbs of R12 should be max. Two small cans.

Could the high pressure side service valve (on the compressor) be damaged or not opening correctly, gasket inside blocking opening?

Are you using an R12 gauge set? The R134 gauges have different readings.

The R134 gauges have different readings.

Is that fittings rather than readings ?

Edit : Following as my A/C seems to kick on once when first started and not again. Suggested to check air gap, but haven’t made it to that and want to see if there are other things I should be looking for with it.

Yes, I am using mineral oil.

Everything on the system was connected and sealed up prior to me working on it, but it didn’t have any refrigerant in it. I don’t mind buying a new expansion valve and swapping it in except for the system is charged with R12 and if I can keep from opening the system that would be best, but I have feeling that might not be possible. Was thinking of calling the garage down the road to see if they can suck the R12 out and temporarily hold it until I get whatever wrong fixed.

I am filling from a bulk R12 container and didn’t have a scale at time of charging, but I was charging off of pressure readings on my gauge and I never saw the low side go above 30 psi so I’m thinking it’s not overcharged, the a/c output air got cool, but never really cold, like what I experience with newer cars when I charge with R134a so I’m thinking it never got fully charged.

I had replaced both service valves before charging, I verified the service port screws screwed in and out properly, but didn’t blow through them so I guess I could have gotten a faulty one.

My gauges are supposed to be good for multiple refrigerants and they have labeling for both R12 and R134a.

One thing I thought was odd was when I was replacing o-rings I disconnected the thing in the picture and it had some sort of restrictor or something in it so not sure if that is supposed to be there or not. I searched the manual and didn’t see any mention of this coupler.

Well cougar friends, another disappointing and unsuccessful weekend for me trying to get the AC to work on my 69. Last week I was having very high pressures on the discharge side in the neighborhood of 400 PSI. This weekend I took everything apart and flushed the whole system with a compressed flushing agent. I also installed a new receiver drier hoping that that was plugged and part of the problem.

I reassembled the whole system but left the discharge hose off. I blew compressed air through the discharge hose and it came out of the service port on the low side because I left it open to see if air would come out. I’m not sure what the problem could be at this point I’m thinking maybe the quick disconnect assembly at the receiver drier, but I did take that apart as far as I could get it apart to clean it when I was cleaning everything else. There’s not much to it it’s just a couple of Springs and sealing discs.

When I ran the car this time I paid attention to the temperature of the discharge line and the condenser. The discharge line and the top half of the condenser got very hot very quickly. I’m kind of thinking that the heat was caused by the pressure not being able to go through the system because of a problem with the quick disconnect fitting assembly?

Any ideas?

I was thinking of ordering another quick disconnect or see if there is a way to eliminate it, but hate to keep throwing parts at it and going through my precious R12. Anyone have any ideas?

If you are still getting excessive high side pressure at idle.

Since pressure equal heat, you should be able to track down blockage/restriction using a thermal temp gun.

Note; when testing watch your pressures so not to harm system any.
Start engine with A/C on and starting at high side of compressor using temp gun follow the flow of freon and watch for a large temp drop. this could narrow it down to either a hose collapsing or clogged condenser.
note; a temp drop at expansion valve is expected.

I usually unplug the compressor at 300psi and let the pressure fall back down to normal before plugging back in. I have kind of done what you are referring to with my hand. The hose coming out of the discharge of the compressor is hot and the top half of the condenser is pretty hot, but bottom of condenser is cool, I think this is normal because I tested my girlfriend’s car and this is how her’s is. Everything else feels normal I guess, the receiver/drier and line to the expansion valve are ambient temp, behind the expansion valve and out of the evaporator core are cool all the way back to the suction side of the compressor.

this is where a temp gun would help, a gradual decrease is normal in a condenser, but not a sharp drop in temp. you may need to follow each core of condenser to find restriction. but it sounds like condenser is your issue causing high pressure.

I do have a temp gun and can do what you say and follow each core of the condenser. I was able to blow shop air through both the condenser and evaporator core when I had them apart, but i had to have the air gun sealed just right or the air would leak around the fitting, I thought this was normal because the air has a lot of pathways to work through, sound normal or not? The thing that gets me is I was able to blow air through the whole system so I guess between that and the high pressures there is a minor clog?

Thunderchero, I did as you recommended last night. First I started out by putting a box fan right in front of the condenser to see if air flow was an issue, no change in pressure. I then got out the heat gun, the top row was between 140*-155* depending on how long I left the system on. I didn’t see any sharp drop in temp; between 5-12 degree drop as I dropped down each row with the higher differences being at the top, bottom was about 85 degrees so right around ambient.

I am wondering if someone put a bunch of stop leak in this thing somewhere along the line, but I didn’t get anything I would think was it when I flushed the system. I was thinking of going ahead and ordering the condenser, expansion valve and the quick connector to have on hand, take the system apart this weekend and carefully inspect everything. My only issue with that is I have a limited supply of R12 and if I end up switching to R134a not sure if it requires a different condenser for optimal operation.

Obviously the expansion valve is dead, and/ or the evaporator is plugged. I would stick with R12, it is much more efficient and the air will be colder by far.

The expansion valve is on my radar and I just ordered a new one along with a few other parts. Can they be partially plugged? I did blow shop air through from the inlet of the expansion valve while hooked up to the evaporator and it came out the other side. I also checked the open/closing function of the expansion valve and that works. With the system running both the inlet and outlet get cold so I know some refrigerant is getting through, just not sure if enough. To me it seems like a minor restriction, but obviously enough to cause problems.

I really want to stick with R12, since that is what was in it factory and the cooling is better than R134a.

I have switched to this after using up my R-12 stash.

One of the small cans gives way better cooling then standard R-12 and there is no regulations or certified people to install it.

I converted my house A/C over to FR-22 and over the last three summers faster cool down and less compressor running.

Doubtful unless a mud dawber got in there. They just seize up in the mostly closed position when they fail, giving symptoms similar to what you have. Or they fail wide open and you never get high pressure at all.

Dang, I was hoping we have found the cause of the problem. I went ahead and ordered a new condenser, expansion valve and quick disconnect to have on hand for next time I open it up; hopefully this weekend if my parts get shipped on time. I was going to inspect everything really well and only use what I thought of those parts I needed, but I might just throw them all on it and if I still have a problem it will be down to the hoses, evap core or compressor, but I doubt it’s the compressor.