A/C Cutoff Switch

[73Coupe]

I've noticed some cars (mostly police) have an A/C cutoff below the dash. I'm just curious why this was needed. In Polaras and other models, did the A/C not shut off when the "OFF" button was pressed (like in Chryslers)?

There's usually a compressor cutoff switch in the head control when the temp slider control is moved to a certain position. Would this do the same truck? Is the separate cutoff switch wired in series with the switch in the head end?

Just looking for some insight on this topic from some of the well-versed folks in the A/C area of this site.

What I'm eventually trying to get at is modifying my head control so that "OFF" really means off. I don't want the compressor running unless I push "AC", and will consider a separate switch as a last resort, for the sake of simplicity.

Thanks for your help, JT

 

[butchr66]

I've noticed some cars (mostly police) have an A/C cutoff below the dash. I'm just curious why this was needed. In Polaras and other models, did the A/C not shut off when the "OFF" button was pressed (like in Chryslers)?

There's usually a compressor cutoff switch in the head control when the temp slider control is moved to a certain position. Would this do the same truck? Is the separate cutoff switch wired in series with the switch in the head end?

Just looking for some insight on this topic from some of the well-versed folks in the A/C area of this site.

What I'm eventually trying to get at is modifying my head control so that "OFF" really means off. I don't want the compressor running unless I push "AC", and will consider a separate switch as a last resort, for the sake of simplicity.

Thanks for your help, JT

Hey I saw that on a '77 catalina taxi I had. What WAS that all about?

 

[commando1]

Hey I saw that on a '77 catalina taxi I had. What WAS that all about?

Towel heads love the heat.

 

[Big_John]

I installed a cut off switch in the 73 Barracuda I had way back when... The reason I did it was because there were no fresh air vents in the car. It was A/C on or nothing. I would switch the A/C on and turn off the compressor so I would have fresh air flowing in the car without it being cooled. Great for night driving (I used to do a lot of that) with the windows down.

 

[MrMoparCHP]

In 69 the CHP just added a note on their switch panel.
So they felt the AC being in the off position was good enough.

Alan

 

[saforwardlook]

C bodies at least in 1973 always had the compressor running even if the a/c was off. It was a really stupid move given the short life of Chrysler a/c systems already. Their concern was about fogging the windshield under some driving conditions if moisture was accumulated in the evaporator and suddenly the driver is unable to see when they turn on the defroster for better visibility. The better solution to this concern was having the switch from previous model years (mounted on the outside of the heater/ac housing) that cycled the compressor on for a minute or so after each restart and then shutting if off. I suspect it was a stupid cost savings to eliminate that switch and go to the always on solution. Just mount a toggle switch, perhaps on the steering column lower cover, with the wires intersecting the wire lead to the compressor and problem solved.

 

[73Coupe]

C bodies at least in 1973 always had the compressor running even if the a/c was off. It was a really stupid move given the short life of Chrysler a/c systems already. Their concern was about fogging the windshield under some driving conditions if moisture was accumulated in the evaporator and suddenly the driver is unable to see when they turn on the defroster for better visibility. The better solution to this concern was having the switch from previous model years (mounted on the outside of the heater/ac housing) that cycled the compressor on for a minute or so after each restart and then shutting if off. I suspect it was a stupid cost savings to eliminate that switch and go to the always on solution. Just mount a toggle switch, perhaps on the steering column lower cover, with the wires intersecting the wire lead to the compressor and problem solved.

What switch was this previous years switch (mounted on the side of the heater housing)?
I would like an auxillary switch to be a last resort. Maybe the solution would lie in installing the switch talked about above, or installing a control head switch from an earlier year.

 

[73Coupe]

1973 fsm...

 

[73Coupe]

If you look at the control chart below, you'll see that the compressor is only shut off when the "HEAT" function is engaged and the temp slider is moved enough to open the compressor cutoff switch (also shown on p. 24-74 below). The OFF button somehow renders the compressor switch useless.

In OFF, it says [compressor] "On above 30*F ambient."

So, in theory, a temp sensor somewhere is really switching the compressor. BUT, per the wiring diagram above, I don't see any other switch. It looks like the clutch power is routed from the main control head to the blower relay. I'm stumped...

Does anybody have an earlier FSM? If so, what does the control chart look like?

Thanks for your help, guys.

 

[Badvert65]

I have a vacuum switch I removed from a 75ish Virginia State Police pursuit vehicle. It was a 440 car and had a vacuum cutoff switch connected to the intake. When you stomped on the gas, the A/C compressor cut off. I think I still have that little bugger somewhere.

 

[thrashingcows]

The AC system in my 68 T/C wagon cycles when the Heat/Def is selected...just like new cars...on for 30 sec, then off for a minute or two. It does this to mix a bit of dehumidified air in with the mix to help keep the windows clear. I can tell you that it certainly does work well. When I was daily driving the wagon a year or two ago it sure helped in the wet winter months. I tried disconnecting the AC compressor to see if it made that much of a difference...within about 10 minutes I couldn't see out of any of the side windows, and barely out of the front. Hooked up the AC compressor and all was clear within 5 minutes.

 

[ceebuddy]

Open Hood. Disconnect compressor clutch power supply by separating plug located approximately 5" from compressor.

 

[73Coupe]

Open Hood. Disconnect compressor clutch power supply by separating plug located approximately 5" from compressor.

Thank you sir for the quick tip. I have had it disconnected at this location since I got the car, and left it disconnected all winter, now the system has lost its charge. I have to rebuild my "rebuilt" compressor and install new seals now. Just did a 400 mile round trip with the wife and no A/C. $1k into my A/C system and still no A/C. "I'm nearing the end of my leash" I've been warned. (!)

Still trying to figure out a "switch-less" solution for the controls though....