1967 Catalina AC Help/Advice

[Jesse315_w]

PLEASE help and/or offer suggestions...I am trying to get the AC back operating on my catalina...(factory spec is 4.12 pounds of R12)..Here is what I have going on...installed a rebuilt compressor, flushed the evaporator, replaced the dryer, replaced the expansion valve...proceeded to pull a deep vacuum (<500 microns)...swept with nitrogen several times and vacuumed again...system held vacuum overnight...loaded it up with 4 pounds (weighed on a scale out of a bulk tank) of R12...freezing up at inlet of evaporator and suction pressure is -4 PSI !...so thought maybe faulty expansion valve...recovered refrigerant and replaced with a new one...no help...replaced the expansion valve again with a known good used one...no help...replaced the POA with a used one...now pressures are 29 on low side and 155 high side with 3.5 pounds of R12...evaporator running at 100 degrees and gets hotter as I add more refrigerant!?!...I have repaired many R12 systems before, but this one has me STUMPED...

[JohnHere]

With pressures of 29/155, you should now be getting at least some cooling.

When you say the evaporator is running at 100 degrees, is that the vent temperature? If so, heated air might be mixing in somehow, possibly a bad blend door, actuator, mis-adjusted control cable, or a bad hot-water valve.

What is the ambient temperature? Is the fan clutch any good? Did you add any oil to the system?

The HP of 155 sounds rather low to me if we're talking, say, an ambient of 85 degrees.

[Dougflas]

You may have hot air passing around the evaporator due to the vehicle being a 1967 (51 years old) and the rubber gaskets inside the evaporator box being bad. Bypass the heater and see if the vent temps drop. To test the POA on vehicle, kill the blower motor. At 1200 to 1500 rpm, the low side should drop to 30ish. I believe that your original POA was bad causing the low side to be at 0 psi

[Jesse315_w]

100 degrees is indeed the vent temperature...I have the vacuum source removed from the heater control valve, but I suppose the valve could be faulty...fan clutch is good and tight and moves a lot of air...I may have better high side pressures if I had fully charged it with refrigerant (stopped at 3.5 this time)...ambient was 80 degrees...mineral oil was added...by my estimation there should be about 8 ounces in the system...I agree that the original POA must have been bad...new seals inside the evaporator box...I will check the operation of the blend doors and will positively shut off the hot water to the heater core....Thank you gentlemen for the responses...these responses are very useful to me as they have me thinking in a different direction...I will update this post as it progresses...again thank you!

[Jesse315_w]

Physically blocked hot water to the heater core and within 5 minutes of running the AC, I had vent temps of 85 degrees and still rising...so the heater core wasn't the issue...I am now to the point that I hate the most, randomly changing out components with new until I find the issue...I cannot think of ANYTHING else to try!....

[JohnHere]

If your ambient is in the 80-degree range but your vent temp rises to 85 degrees and higher in a short time, it seems to me that heated air is still making its way into the system somehow. If it wasn't doing that, the vent temperature would be about the same as the ambient, assuming that the A/C was turned off or otherwise not cooling up to par.

Try this: Start the engine and let it warm up, shut off the A/C to ensure that the compressor doesn't run, set the temperature dial or lever to maximum "cool" in the blue zone, set the blower on medium, set airflow to discharge through the dash vents, and then measure the vent temp. If it's noticeably higher than the ambient and keeps rising, you're still getting heat through the system.

I know you said that you blocked water to the heater core, but if the heat is still on, even partially, that'll be more than enough to overcome any cooling, especially if the A/C isn't working right.

I wonder whether the hot-water valve is installed backwards, which could compromise water flow and result in heat when you expect ambient or cool air. It's easy to overlook something like that.

[bohica2xo]

When I see a POA system with 29psi low & 155 psi high, all I see is an evaporator with no airflow.

Is the suction side cold?

Do you have a low side port on the compressor side of the POA? Not all systems have this, but some do.

If you raise the engine RPM to 1500+ does the evaporator stay at 29psi?

[Jesse315_w]

Replaced the water flow valve with a known good one and used flat jawed vise grip pliers to clamp each water line shut...I am running this car with the rear half backed out of an enclosed garage, so the vent air supply is probably picking up the engine heat...I guess my next step should be to remove the evaporator cover and verify that the door is open and air is moving across the core and not not bypassing it.

[Jesse315_w]

Verified that full airflow is moving across the evaporator... bohica2xo, when you say is the suction side cold...specifically where on the suction side are you referring?...I have cold at the expansion valve and into the bottom of the evaporator...100 degrees at the discharge elbow of the evaporator with a full refrigerant charge...this system is working like a heat pump!

[bohica2xo]

There it is. The TXV is passing just enough liquid to make the evaporator inlet cold...

If the suction line to the POA is not cold & dripping, the evaporator is starving for refrigerant. The POA is holding 29psi, but I suspect the compressor side of the POA is in vacuum.

Time to recover & bench test that TXV.