AC Diagnosis help

[MooseStang]

My L code isn't blowing cold. Can somebody look at these gauge readings and point me where the issue may be? 1st pic engine running, 2nd after engine off for about 5 minutes.

 

[MooseStang]

R12

 

[Mike King]

High pressure readings for both low and high side with engine and a/c operating. Possible causes include:

1. Over charged
2. Condenser malfunction-internal restriction.
3. Condenser malfunction-restricted airflow through fins
4. Tx valve stuck open.
5. restriction in high pressure side between compressor discharge port and receiver drier inlet.
6. Excessive air and/or moisture in the a/c system.

Just for your interest at 100 degrees fahrenheit the static (not running) pressure reading should be around 120 PSI for R12.

 

[Steve McMahan]

Those readings are not off my much, you should still be getting cold air unless the fan air is not moving over the evaporator coil or the coil is frozen. You say the airbus warm? Can you put a temp gauge in the airstream to see what it is? The R12 pressure reading on the low side usually correlates to the temperature of the evap coil.

30 is at the lower end, should be 30 to 40. It might be a bit low on R12, but if you’re not sure, some systems have a slight glass, usually near the dryer, you can observe the Freon moving by. If it looks like bubbles moving, that usually means it’s low on R12. In any case, if you’re not sure, I would take it to the shop. Steve

 

[mrgmhale]

Those readings are not off my much, you should still be getting cold air unless the fan air is not moving over the evaporator coil or the coil is frozen. You say the airbus warm? Can you put a temp gauge in the airstream to see what it is? The R12 pressure reading on the low side usually correlates to the temperature of the evap coil.

30 is at the lower end, should be 30 to 40. It might be a bit low on R12, but if you’re not sure, some systems have a slight glass, usually near the dryer, you can observe the Freon moving by. If it looks like bubbles moving, that usually means it’s low on R12. In any case, if you’re not sure, I would take it to the shop. Steve

Funny things, speaking of sight glasses with automotive A/C systems... On our 69 Shelby GT500 with factory A/C, when we got the car about 7 years ago the A/C was not working. Being that I got it from Ottawa, Canada, the seller was not able to get anyone to work on the R-12 system unless he allowed them to move to R-134, which he did not do (luckily). I pulled a vacuum on the system, overnight, then shut off the vacuum pump and let the car sit with the vacuum in the A/C system for a few days to see if it had any leaks (other than under positive pressure). This was after I installed a new Receiver/Dryer and Condenser (original condenser had some damage to its cooling tubes and fins, nothing that opened the system to the atmosphere, but I prefer to not have to straighten out all the dented cooling fins from over the years).


After verifying the A/C system was not leaking the vacuum I installed some R-12 I purchased via ebay, which has a lot of Japanese linguistics on the can - but it was labeled as R-12, and it worked well. I do not recall off hand how much R-12 was supposed to fill the system, it is on a factory tag on the compressor (per the photo attached 1 3/4 pounds of R-12). But, I did note that after I installed that much R-12 I was getting a lot of bubbling under the sight glass. So I added some more R-12 to see if I could get it to become solid. I never did get it to run clear, and I ended up having to remove some of the added R-12 as the system had become a little overcharged. I do believe that is the first time I was not able to rely on the sight glass to establish when the system had enough, and not too much, R-12.

The good news is the 69 GT500 has factory A/C, something I was looking for when I began to look for a 69-70 GT500 (my first big block Mustang/Shelby, and my last. I love the torque, but it is so hard to work on the engine because of how tightly it is stuffed into the engine bay). The other good news is the A/C works well, and I have not had to recharge it because of any leaks. The only things even close to being bad news is I do not feel I can depend on its sight glass to properly charge the system. Things could be worse...

I have found those older Ford A/C systems are pretty durable...