Ok guys, I am about at my wits end with this AC system. My 82's AC system has been almost completely replaced between me and the PO. In 2011 the system was converted to R134 with all hoses replaced, new compressor, new dryer, resistor pack, rebuilt HVAC control unit and rebuilt HVAC blower. The car sat until April 2013 due to a leaky gas tank, so the AC did not work when I bought the car. Since then, I have replaced the compressor (leaky seals), dryer, hi and lo pressure switches, expansion valve and new o rings around. The charge was checked today and is full with no leaks anywhere. However, the system blows very cold air only sporadically. To get the system to work, I must move the temp slider to hot and then to cold. Then the it will blow cold, but not all the time. A mechanic said the AC temp controller? under the driver's knee may be faulty. I have most of the interior out now and I can put my hand on the controller while in the drivers seat. Could this be a vacuum leak, HVAC controller or what. Thanks!

 

First determine if the issue is with the refrigerant system or the temperature control system. When the A/C running does the compressor clutch engage and are the system pressures and refrigerant line temperatures correct per the WSM? Does moving the temp control slider in the A/C control head from hot to cold and vice versa cause the temperature setting motor to cycle through the full range of travel?

Mike

 

There is a little "arm" that connects to the temperature setting motor. (The temperature setting motor is the picture I've attached.) It rotates to the 'up' position for hot air, 'down' for cool air. The arm controls the heater box flap.

I would do what Mike said in the previous post: get on your back with a flashlight, looking up. Have a friend move the temperature slider to various positions and see if the temperature setting motor moves the lever- or not.

 

It isn't a refrigerant issue, all that has been checked. The compressor is working fine, it should be as it is new. The ac fan is working, freon pressure was checked today and all coolant lines are very cold to the touch. I have checked the arm moving when you select econ from off and to cool and moves again when selecting defrost. The recirc flapper is also working as it should. Roger told me to check the outside temp sensor in the left wheel well and hard wire the heater valve to closed. We will see if I get cool air again. Any other suggestions?

 

Ok I was looking at the right side of the HVAC controller and the arm moved when selecting econ, auto, etc. But when looking at the left side the arm did not move at all when changing the temp control from cold to hot. So is that a bad temp controller and maybe contacts needs cleaning? Is this part available? I'm about to finish pulling the seats out to redye everything, so access to the controller will be much easier in a few days. Suggestions? Thanks.

 

Any help with the above question?

 

There is a.detailed troubleshooting guide for the temp control circuit in the WSM.

Mike

 

From WSM:

Disconnect plug 2.
Ignition on.

Terminal 4 to 12. At around 70 degrees, 3700 ohms when slider is set to cool, 4700 ohms when slider is set to hot.

If resistance reads infinite, "there is an interruption in the sensor chain which comprises the internal sensor, external sensor, and operating switch."

"If the reading of the ohmmeter is smaller by a significant margin there is a short in a sensor or in the operating switch."

Internal sensor is the little round thing at the top of the center console. External sensor is in the alternator cooling hose. Operating switch is the temperature slider.

With plug 1 connected, check:
Terminal 3 to ground: battery voltage
Terminal 8 to ground: battery voltage
Terminal 2 to ground: battery voltage
Terminal 9 to ground:
- Slider set to Cold: battery voltage
- Slider set to Hot: voltage should be 10% of battery voltage
Terminal 10 to ground:
- Central vent open: 0 volts
- Central vent closed: battery voltage
Terminal 1 to ground:
- Central vent open: 0 volts
- Central vent closed: battery voltage

When I did this test, my HVAC setting motor failed. The following thread helped me a lot
:
https://rennlist.com/forums/928-foru...w-working.html

 

The AC is now blowing very cold, thanks for everyone's help. Come to find out, the outside air temp sensor was not connected within the rubber boot. Seems a mechanic friend of mine trying to help me out with a charging issue pulled too hard on the alternator cooling hose while testing the alternator and must have disconnected the lead. Just like the instructions, there was a short between the temp setting motor and the sensor after testing the resistance between 4 and 12 pin on the setting motor. So I fixed that and took the setting motor out for testing just in case. My aircraft mechanic/electrician tested all the circuits, components and powered up the motor with 12 volts, all good. After I timed all the flaps, we got good AC. Very frustrating that one little wire in the wheel well will prevent the whole AC system from working. Now on to a faulty fuel sender and interior.