I have a 1982 300TDT. She's having problems with the a/c. About 40% of the time it works great. The other 60% of the time, it blows hot. Really hot. I can see the compressor turning, and one time the aux fan even kicked kicked in. Where should I start looking for the fix? I replaced the CCU because mine seemed a little wonky, but it didn't fix the problem.

Thoughts? As usual, thanks so much to you experts. I wouldn't be able to service this awesome beast without you!


Thanks!

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'90 300SE --- 173k miles --- (Odometer just stopped working!)

'85 Cali 300D --- 193500 miles --- (Second one) Sold Nov '10

'82 300TDT --- 236,xxx miles --- (My first one) Sold July '09

1984 300d Turbo 144,000,
New Rebuilt Engine And Transmission
Your Mono Heat Valve Is Leaking Hot Water, On The Firewall Next To Battery Buy A Monovalve Kit $44.59 THIS SITE P/N R3023-15174 And 1/2 Hr Done Diy.

The compressor always spins, but it free wheels if the AC is not on. There is a clutch inside the compressor wheel that kicks on and actually turns the compressor when you turn on the AC. Are you sure that the clutch is working, and the AC is actually turning on? The RPM should jump up a little when the compressor kicks on.

Also there is a pressure switch on the receiver drier that will not allow the compressor to turn on if the AC system pressure it too high or too low. Keeps the compressor from burning itself up. You might check to make sure the switch is working properly. You can jumper the two wires that are connected to the switch, and then put a volt meter on the connector on the compressor and see if you get 12V when you jumper the two wires.

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I think Raymond is all over it, if in fact the compressor actually kicks on. The aux fan coming on would indicate heat from the condenser, which makes compressor operation likely.
Make sure it is coming on, as per Andrew, then check monovalve.

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

If the air is heated rather than ambient, then I suspect you have a problem with heater control rather than AC.

With the temperature dial on min, and AC switched on, remove the electrical connector from the top of the monovalve. You should have 12V on one pin relative to ground and continuity to ground on the other pin. Or it should light a 12V bulb brightly if you jumper it between the two pins. If you fail this test then you have a CCU or wiring problem as the monovalve needs 12 v across those pins to close it and stop hot water entering the heater core.

Then check the monovalve insert as recommended.

If the monovalve insert is OK, apply 12v across the monovalve terminals with the engine switched off. You should hear a thunk as the monovalve operates.

If all this fails to show a culprit you could have a problem with an intermittent connection in the monovalve solenoid coil, insert jamming within the monovalve body or in the wiring between the CCU and the monovalve. This is the stage I am at with exactly the same issue. I am now considering replacing the whole damn thing to see if that will fix it!!

I was having intermittent cooling. Cooling on startup then shutoff and warm, but not hot air, on highway. Really HOT air is probably a monovalve leak and can be fixed according to previous posts. I went through the monovalve issue and finally fixed that, then "topped off" the 134a this spring, during relative cool ambient temps. When it got really hot here and I was still having problems, and I also was thinking of buying a complete monovalve. Instead, I just took it to the local Indy and told him the history and "fix it" then held my breath.

He called and said it was fixed, that I had overcharged it and the compressor was shutting off after working for a bit due to too much pressure. He charged me $65 to test the system and bleed off the excess freon, but he also gave the car a good going over and had some useful observations and suggestions, and I believe it was well worth it. He also found a slow leak in the condensor, so I can plan for that in a couple months. The AC system is not really suited for south Louisiana summers (or Houston) even when it is optimal, but it can be made to work. And sometimes going to your local Indy can be a wise decision, though I fought it for a long while.

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1983 CD
1958 Studebaker Packard (being resuscitated)

Thanks for all the suggestions. I ordered a new monovalve. Hopefully that fixes it!

I wouldn't mind taking mine to an indy shop for a/c. I don't think I'll ever trust them with anything else under the hood though!

__________________
'90 300SE --- 173k miles --- (Odometer just stopped working!)

'85 Cali 300D --- 193500 miles --- (Second one) Sold Nov '10

'82 300TDT --- 236,xxx miles --- (My first one) Sold July '09