AC not working

[vandenham]

My AC has not worked since getting my car (1978) a couple of years ago. I am trying to figure out where the problem is.

The circuit diagrams say power goes through the the AC switch using the following path:

• Fuse board (J1) to AC switch
• AC switch to AC temperature switch
• AC temperature switch to fuse board (J2)
• fuse board (J2) to fuse board (Q2) through AC relay
• fuse board (Q2) to AC pressure switch
• AC pressure switch to pin 9 of 14 pin connector
• pin 9 of 14 pin connector to AC clutch

I have tested the continuityof the first four (between J1 and Q2) and find I have 12V power switching off and on with the AC switch. Great so far. Here is a picture of my fuse board - I was surprised that the AC pressure switch (position XI) is just a jumper.



Power is supposed to go from Q2 to pin 9 of the 14 pin connector through the AC pressure switch, but pin 9 is dead. I cannot figure out where the AC pressure switch is located so I can confirm/check if power is getting through there. Can someone tell me where to look? THANKS

I thought that this switch was the AC pressure switch (located passenger side in front of the condenser). PET calls it the low pressure switch (959 613 137 00) - but when I directly connect the two connectors it drives the fan in front of the condenser. This matches with the wire colors and function in the circuit diagrams where this is called the Temperature Switch - Refrigerant.



I'm sure the AC pressure switch is hidden under the hood somewhere. Any help you can give will be appreciated. I will be hunting some more tomorrow.

Thanks,
Rick

[JhwShark]

It's hanging from the crossbar pasenger side...The hose with the coilover goes to it and the wires connect from below.

[vandenham]

I don't have anything hanging off my crossbar although it appears something might have been there in the past. Is this part number (928-606-215-01)?






I will look tomorrow to see if I can find two unconnected wires. Maybe I can short them out to see if I can get the compressor to engage. Looks like I am going to be buying a bunch of parts to try get this part of the circuit working for my AC.

Rick

[MPDano]

Are you sure that's called a Pressure Switch. The Solenoid hanging from our Crossbar just raises the idle when you use the Ac.

[MPDano]

Rjm65's 79 also doesn't have that Solenoid. Hmm, but JhwShark 79 does. Weird.

[vandenham]

Are the black hoses coming out of the unit vacuum lines?

[Fredfox]

Relay on temp controller head bad?

[JhwShark]

Originally Posted by vandenham

Are the black hoses coming out of the unit vacuum lines?

Yes, vacuum...I believe the device I showed is called the Supplemental Air Valve, AC...a solenoid type

[MPDano]

The thing is, that solenoid hanging off the crossbar will not keep his AC from working. It only makes the idle a little higher to compensate for the AC Compressor stress on the engine. Some 928's don't even have it, so I it's not even necessary.

[JhwShark]

Originally Posted by MPDano

The thing is, that solenoid hanging off the crossbar will not keep his AC from working. It only makes the idle a little higher to compensate for the AC Compressor stress on the engine. Some 928's don't even have it, so I it's not even necessary.

Thanks...good to know what it does...not his problem

[vandenham]

There is a wire going from Q2 on the fuse panel to the 'Supplemental Air Valve' and then from the 'Supplemental Air Valve' to pin 9. The 'Supplemental Air Valve' is turned off and on by the AC switch to speed up the idle (I suspect this might only apply for automatics).

If the 'Supplemental Air Valve' is disconnected, then there will be no power to pin 9 when the AC switch is turned on and the AC will not operate.

In my case where there is no 'Supplemental Air Valve' I would expect Q2 on the fuse panel to connect directly to pin 9. I just looked at the cable loom going from the firewall to the 14 pin connector and cannot see any place where two wires (should be black) exited to hook up to a 'Supplemental Air Valve'.

I suspect I have a broken wire in the loom or a bad connection to pin 9 in the 14 pin connector. Later this afternoon I will check the 14 pin connector and work my way back to the fuse panel.

Rick

[vandenham]

Ignore my last post. MPDano you are correct, the unit hanging from the crossbar is not related to the air conditioning system.

I did some more reading and finally located the low pressure switch. I had thought it was temperature switch on the receiver/dryer located passenger side in front of the condenser (picture in my first post). But there is a second switch located lower down on the receiver/dryer and it is the low pressure switch. You can see it by looking through the grill.



The good news is that I bypassed the switch and my air conditioning compressor came on and worked when I ran the engine. No strange noises - hurrah!

Now I know that I am low of refrigerant - I am going to get a pressure tester to see how bad the situation is. The glass shows there is fluid and there are no bubbles. Maybe it is just a matter of adding more refrigerant.

Red Tek makes a product to seal leaks www.redtek.com

Would it be a good idea to add something like this to my AC system to bring it back to life? The AC has not worked for the three years I have owned the car and I don't know when it last used before that. After I find out the pressure levels, I will know better how bad the problem is.

Rick

[MPDano]

Originally Posted by vandenham

Ignore my last post. MPDano you are correct, the unit hanging from the crossbar is not related to the air conditioning system.

I did some more reading and finally located the low pressure switch. I had thought it was temperature switch on the receiver/dryer located passenger side in front of the condenser (picture in my first post). But there is a second switch located lower down on the receiver/dryer and it is the low pressure switch. You can see it by looking through the grill.



The good news is that I bypassed the switch and my air conditioning compressor came on and worked when I ran the engine. No strange noises - hurrah!

Now I know that I am low of refrigerant - I am going to get a pressure tester to see how bad the situation is. The glass shows there is fluid and there are no bubbles. Maybe it is just a matter of adding more refrigerant.

Red Tek makes a product to seal leaks www.redtek.com

Would it be a good idea to add something like this to my AC system to bring it back to life? The AC has not worked for the three years I have owned the car and I don't know when it last used before that. After I find out the pressure levels, I will know better how bad the problem is.

Rick

Oh man, I totally forgot about this switch. I put an AC belt on my "S" today hoping it would just work, but no go. Clutch never engaged and forgot you can bypass that switch to test the clutch. Glad I read your post. Did you have to remove your grill to get to bypass the switch?

[vandenham]

No, I just reached in and pulled off the connectors. Then I put an alligator clip on the two terminals. I could hear the magnetic clutch click when I turned on the AC without the engine running.

And the compressor ran with the engine running.

[MPDano]

Originally Posted by vandenham

No, I just reached in and pulled off the connectors. Then I put an alligator clip on the two terminals. I could hear the magnetic clutch click when I turned on the AC without the engine running.

And the compressor ran with the engine running.

Excellent! Ran a jumper and turned my AC to Auto and Bam, the AC Clutch engaged. This is great news for me. Thanks for the tips.

[vandenham]

MPDano - good news.

I am trying to figure out what to do next. Are you going to recharge it yourself or seek professional help? I believe the professionals will want to convert from R12 to R134a - $$$$.

[MPDano]

Originally Posted by vandenham

MPDano - good news.

I am trying to figure out what to do next. Are you going to recharge it yourself or seek professional help? I believe the professionals will want to convert from R12 to R134a - $$$$.

Converting to R134a is not hard at all. Really all they do is changeout all the seals, which I did on my Grey Euro, I then took it to a real good Pro AC Shop near me that knows the 928. They Evac the System, Charge the system with oil and r134a. Mine also needed to replace the expansion valve. They did a great job and I got cold AC again. I'm going to drop it off to them sometime soon.