Hondo

Hi Gang,
I just got my car back from the Transmission Shop, I was just making sure the AC was working, and it was so I turned it back OFF, also checking lights, wipers, etc.
then when i got back home opened the hood and noticed AC Pipe was frozen?
One of my friends said that's how the 1970 Olds AC works, you actually have to shut off the car to turn the AC OFF? is this true and also said it was fixed in 1971 etc..

Thank You

69HO43

Whut? Never heard of that untrue statement of having to turn the car off to get the compressor to disengage. If you put the selector switch all the way to off it should disengage the compressor, and freon flow should stop. Sounds like for whatever reason, the switch isn't getting in the off position or if it is, something has welded itself together to keep power to the compressor clutch for some reason.

See if the compressor is turning when the controls are in off with the engine running. If so, you'll need some further troubleshooting.

Depends on your outside temperatures I guess, but it appears as such the freon may be a little low as it seems to be freezing up at the POA valve. JMO from the picture. Ideally, it should be cold, but sweating. Nothing to worry too much about as it does seem to turn on and work. Just not sure if it's turning off.

70Rocket

Yes, that is correct. Once engage, the compressor on your 1970 cutlass will not disengage until you turn off the engine. Once turned on, the relay on the passenger fender remains energized even if you turn the interior switch back to off. Its because the main power to the relay will continue to energize the circuit.

In my opinion, its is a design flaw in the circuit. I thought there was a problem with my own car years ago when I observed the same issue. But, after researching the problem, reading the Olds service manual, and studying the circuit diagrams, I realized it is just how the system works.

I have also occasionally observed frost / ice on my AC.

Bubba68CS

From the way it was explained to me by my AC guy, the reason it works that way is to provide dehumidification for the defroster. You turn the control to AC first, then to defrost. Apparently a lot of people just bypass it. You lose that dehumidification option, but it does turn off when you turn off AC.

joe_padavano

^^^THIS. The always-engaged compressor is a well known design issue.

Fun71

I also found this operation on my 1970 Supreme back in the 1980s. I did not like the idea that the compressor stayed on when the dash switch was turned off, so I wired a toggle switch to the compressor feed so I could disengage the compressor without turning the ignition off. I read a while back here on the forum there is a modification to the hold-in relay that will accomplish the same thing, but I don't remember the details.

70Rocket

There is a wire in the passenger fender mounted relay that you can cut to change the operation. I would have to look at the circuit diagram again to figure out exactly what to cut. I never bothered to modify the circuit in my car.

matt69olds

The wire you need to cut is inside the relay itself. You need to carefully pry open the tabs that hold the relay cover to the relay body. If you look closely at the insides of the relay you will se a tiny jumper wire that goes from the green wire (power out to the compressor) to the trigger wire (I think it’s green with a white tracer?) that is the trigger wire from the A/C control head.

Once the compressor is engaged, power from the compressor feed will go thru the jumper wire back to the trigger wire, keeping the relay energizer regardless of the control head switch. Cutting the jumper eliminated the compressor power back feeding onto the relay coil. This is outlined in the service manual far better than I can explain it.


The story I was told is Olds designed the cars like that to keep the windows from fogging up when you shut off the A/C. I guess the evaporator core warming up raised the humidity level enough to fog up the glass. Seems to me if that ever happened, the driver could obviously slide the controls to defrost to clear the windows.

They didn’t design the later cars with this “feature”. I’m guessing with the drop in compression, lower engine output, and the demands for ever better fuel economy made the previous thinking obsolete. Kinda hard to pull maximum performance and economy out of a engine if you can’t shut off the A/C!

matt69olds

As for the A/C freezing up, your probably going to find the system slightly undercharged, or moisture in the system. There is a sight glass on top of the accumulator in front of the radiator. You can see the sight glass thru a small hole (about the size of a quarter) in the core support. If I remember correctly, your suppose to add refrigerant until you no longer see bubbles in the sight glass (A/C on of course, max cool, high blower) and then add 1/2 pound of refrigerant.

This is assuming the system hasn’t been converted to R-134. If so, I would do a little research before touching the a/c. I’m sure someone in readerland knows far more about A/C than I do.

Hondo

Wow Awesome ALL the Answers are great! I appreciate all the ANSWERS..

is there any Video's or steps (Pictures) on how to rewire the RELAY to make the AC Work the right way??

Hondo

are you talking about relay behind power booster?

thank you

Fun71

Correct, I think 1970 was the last year for that. I know my 1971 Cutlass does not have it.

That was exactly my reasoning for adding the toggle switch back in the early 80s.

Fun71

No, not that one.

Love1955oldsmobile

Here is a simple fix to my 1969 98 compressor continue to remain engaged after "turning off" the a/c on the control panel. While in a forward gear like drive, turn the ignition switch to the start position. The neutral safety switch should prevent starter engagement and at the same time it disengages the compressor clutch holdin relay. Try it - you will like it and its already built into the greatest car ever built. No rewiring - cutting wires. Just a simple twist of the key. Ron

Hondo

Hi Ron,
so the starter wont TRY to turn? wouldn't that make your starter grind tying to restart?

Fun71

No, the NSS prevents the starter solenoid from engaging when the shifter is in a drive gear.

This is an interesting idea. Wish I had known about it 40 years ago.

matt69olds

It is pretty clever. Just make sure the NSS is adjusted correctly!

Love1955oldsmobile

I am not sure how i stumbled on this method. I was still regularly driving my 69 98 around until 1989. Some where around the oil embargoes i needed to save gas and i think i traced out the a/c circuit but at 71 i just don't remember. This works standing still or at 100 mph - i have done both. But i saw the message here and replied. A bit of knowledge that might help others. As a side bit, the a/c never leaked as the compressor was well lubricated by this method long before computers did the 5 minute run for us. Ron

Love1955oldsmobile

One final thought. Olds likely dropped the idea as it would save a bunch of money - the relay - the plug - the wiring - mounting screws - the assembling labor. 😀😀😀😀 Ron

Love1955oldsmobile

Did Buick and Cadillac do the same thing in those years (compressor continues to run after switching off at control panel) since the a/c systems were very close in design? Then this idea would help our GM buddies. Ron