Mr. Goodtool

On my 72' 442 Cutlass-s, the compressor clutch would not engage. I tracked down the wiring, checking continuilty on componets and found that if I disconnect the black "superheat" switch wire from the back of the compressor, it will. Keeping in mind that everything's cold, engine & compressor, what doe's this mean? Can the superheat switch be bad? and if so, be replaced? or is this a sign of an over/under pressure condition in the freeon?? The thermal limiter fuse, is ok too.
Also, the med.-high fan speed doesn't work. I replaced the fan relay [behind the brake booster, on the firewall] but still nothing. The highest speed kept blowing the [short] 30a fuse, so I installed a self resetting 30a breaker attached to one of the wiper pump's four screws.
Tech heads, HELP!!!

Lady72nRob71

It sounds like you have an underpressure condition. When this happens, the switch closes and passes current through the thermal switch. If the condition remains for a certain amount of time, the the thermal fuse will open, disabling the compressor.

Did the thing blow cold before this happened?

Remove and check the blower resistor for obvious damage. It is mounted on the outside of the a/c box in the engine bay - has 3-4 wires going to it. Kinda hard to get to but it is possible.

If the 30A fuse kept blowing, do not use high speed until you find out the reason.
A fire hazard is brewing.
It is possible the blower motor bearings are dry or worn and the excessive load is causing it to pull excess current.

Have an ammeter handy?? If so, remove the A/C heater fuse and install the ammeter across it. Activater VENT position and make note of LO current and med-lo current readings. Post them and i will compare with my data.
Excess motor current could have caused the resistor to open, too.

rocketraider

Those superheat switches cause more problems than they solve. They're designed to protect the system from a low refrigerant charge condition so you won't cook the compressor, but my experience is that they will invariably blow the thermal limiter fuse on the hottest day of the year when the A/C system has the correct charge.

I've had mine disconnected and taped for years, and one of the cars even has the thermal limiter fuse clip jumpered to keep from unnecessarily blowing it.

And I no longer have to replace thermal fuses on the side of the road. Used to keep a minimum of three in the glove box for such an occasion.

Mr. Goodtool

Thank you both so very much!
The car sits for long periods,[mostly between local car shows] and the occasional "sunday drive". I have ran the air for about a half hour each time for upkeep. Before last year, I had the air serviced, when it had gone out. They said it needed a "pound" of freon, & new thermal limiter fuse. it lasted one summer, then quit again, at the beginning of this summer. Do I check the pressure at the schrader valve port at the back of the compressor? and what should it read? THANKS!
This was my mom's car off the showroom floor!

Mr. Goodtool

Oh yeah, No Ammeter...Im sure the bearings must be dry, can they be "re-lubed" in place? or are we talking massive teardown, and replacement.
Thanks again!!

Lady72nRob71

Sounds like it is leaking out quickly. With the age of the rubber seals, it is no surprise that it can no longer hold a charge. The leak needs to be found and fixed before continuing to charge with costly R12.
I believe the suction side valve is on the POA valve. I think it should read about 35 -45psi but I would need to consult the service manual chart to be sure. It varies depending on ambient temperatures.
The compressor valve is the high side. Readings should be between 200-350psi depending on ambient temp.

The fan motor is behind the right front fender - a PITA to get in and out without removing the hood and fender.
Once you get it out, it is best to just replace it.
Would be nice if you can check the current before condemning it.

rocketraider

Acceptable leak back in the day was "up to a pound of Freon a year", and that was actually pretty close considering seal technology of the time.

Another thing that can help is to rotate the compressor every so often while it's idle for winter. That was one of two reasons the compressor was incorporated into the DEFROST controls in the early 70s- the defroster blows dehumidified air in DEF position and the compressor gets some exercise.

Mr. Goodtool

When I jumpered the thermal limit fuse, with the superheat switch wire disconnected, the compressor kicked in when switched on, and after a few seconds, the air started blowing very cold.

rocketraider

Tape the stupid thing off so it can't ground on anything and blow the fuse again, and enjoy your a/c!

Mr. Goodtool

Can the superheat switch be replaced without lousing freon, in place?

Blair442

For changing the fan blower motor I have removed the pass side inner fenderwell and it's easy access.

Blair442

I have an issue with my 69 Vista Cruiser where the AC stays on when I pull it back into vent. It will only shut off when the key is turned off and then back on again. The relays are new( er ). I changed the selector and the fan motor. Also the high fan Fuse blows and theFan selector switch gets HOT! Help!

rocketraider

Your Vista Cruiser is behaving normally. Those years have a compressor hold-in relay, for whatever reason I've never heard or understood, and once you've turned on AC the only way to get the compressor to disengage is to put the control in a non-AC position and shut the ignition switch off. I think Oldsmobile was the only GM Division to use it.

I bypassed the one on my 69 Toronado years ago because I was tired of the compressor running all the time. The only time the feature ever came in handy was if you wanted to run the compressor in defrost position. It did clear the windows quicker.

You've got something screwy in your high blower wiring. In high speed, the fan switch serves only as a trigger for the high blower relay and should carry no high current load, certainly not enough for it to get hot. The relay connects the blower direct to battery voltage via the junction block power post and bypasses the blower resistor completely in high speed position.

Do you have a wiring diagram, and did you get the correct relays? My experience is that oftentimes on older electrical apps, what a parts store's computer says ain't necessarily so.