1972 A/C relay

[RWCearley]

I have an NOS relay for the A/C compressor for a 1972 chrysler. I have a 1971 chrysler new yorker which does not have this relay. It never seemed to be a problem without it. Should i install this relay?

 

[Trace 300 Hurst]

Yes. I did exactly that to take the amperage load off of the whole system using an aftermarket relay (not a very cool Mopar unit like yours!). I went to the alternator post for the direct source and hid the relay and wiring under the receiver/dryer. This allows you to use the original wires to the Low Pressure Cutout Switch to provide the "trigger signal" to the relay and send direct juice to the clutch. I did all this to look 100% OEM to any casual observer.

Otherwise, the nice directions that are provided will get you the same wiring schematic upgrade.

 

[Trace 300 Hurst]

I went to the alternator post for the direct source and hid the relay and wiring under the receiver/dryer. This allows you to use the original wires to the Low Pressure Cutout Switch to provide the "trigger signal" to the relay and send direct juice to the clutch.

I should add that the Low Pressure Switch is still functional with my electrickery setup, as it is "in series" with the 85 and 86 trigger terminals on the relay.

Pic stolen from the Interweb....this isn't my artwork:

 

[Rubatoguy]

Is the only function of this relay to reduce the load on the wiring in the vehicle? Similar to wiring your headlights through a relay so you don't have the full amperage running through the headlight switch.

Do these cars have a vacuum switch to disengage the A/C clutch when the accelerator is floored or the engine is under a high load?

 

[Trace 300 Hurst]

Yes, use of the relay removes nearly all of the load from the wiring, bulkhead connection and other connectors, the AC switch, the ammeter, etc. Just like your headlight example, the only juice that is now in the circuit is the tiny bit feeding the relay.

No vacuum switch or compressor On/Off control back then. The AC was always on (not counting AutoTemp and other attempts at compressor control). Other makes might have had a simple vacuum switch....dunno.

 

[CBODY67]

ONLY the for-real law enforcement vehicles had an instrument panel switch to turn the compressor off. Whether factory or installed during the "make ready" period for those vehicles. "Civilian" vehicles did not have visible switehes.

There is ALSO a compressor "on-off" switch in the heater control cable, which is a two-piece cable rather than the prior 1-piece item. As you move the heat lever just past the 1/2 way position, a slight "click" can be heard and also felt in the cable. Have to be paying attention to notice it! But it is there. I discovered this on our '72 Newport Royal (manual) factory a/c car. The water valve cable end is easy to reposition to keep the valve closed, but with the inside lever just past the 1/2 "hot" position. An easy "fix" that looks a bit unusual in the summer time.

Staging the switch to keep the compressor "on" at the lower heat settings provides de-humidification during less-hot times of the year. If more than 1/2 heat is needed, no need to have the compressor competing with the heater core to get things warmed up, I suspect.

Enjoy!
CBODY67