Last Friday I completed a basic restoration of my HVAC system.
The AC works as it should(?) and so does the heating part of the system. All of the controls are functional as the HVAC system responds to all of the inputs.
However, I noticed that my AC compressor never shuts down. Whether I have the AC or the heater on, the compressor stays engaged with the switch in LOW. AUTO or HIGH.
In the OFF position everything shuts down as it should.

a)Is this normal?
b)Shouldn't the AC compressor cycle on and off?
If the answer is (b) what should I check for?
BTW: there is no pressure switch at the back of my AC compressor, which I assume is there to shut the compressor down if AC pressure get higher than it should be.

 

The AC compressor is always on. The car uses it to dehumidify the air before it enters the cabin, even in heating mode. (I'd say more, but you've exhausted my knowledge.)

There is a fresh-air modification described on Jag-aire. https://www.jag-aire.com/

 

Nothing more to say. That's it !

Cheers
DD

 

As mentioned it is normal for the compressor to always be engaged.

If the evaporator ices up the "Ranco thermostat' will break the circuit until things defrost.

Your car would originally have had a 'superheat' switch at the back of the compressor. If it isn't there then I suspect the compressor has been replaced but the switch not transferred from the old compressor. The switch works in conjunction with the three-pronged thermal fuse (perhaps also missing on your car?) to shut down the compressor if the freon gets too low.

Late Series III cars used a HSLP (high side low pressure) switch in place of the superheat switch. The HSLP type did not use the thermal fuse.

The earlier superheat type compressors are often replaced with the HSLP type compressor.....the wiring modification is very simple. However, since yours has no switch at all you'll have to determine for sure which compressor you have....which won't be easy with it installed in the car. You have to look in the hole where the switch goes to see if the orifice is in the center of the hole or offset to one side.

Cheers
DD

 

I was doing some work in my engine bay and just to follow up on my AC, I do have the three pronged thermal fuse connected.
With the temp switch set at 65, and the AC control in the Auto/High/Low mode the AC compressor stays on all the time. Temperature at center vent is 38 -40 degrees.
However, if I change the temperature switch to 75 degrees or higher the AC compressor will cycle on and off and the vents change to the sides and foot well.
Is that how it is supposed to work?

 

That's how mine seems to work, but someones messed with it a bit from the rats nest of spliced wiring around the rebuilt compressor.

 

That's good!

As built there's no cycling function as seen on many more modern systems. However, if your evaporator is icing up the Ranco thermostat will break the compressor circuit....and then close the circuit when the evaporator warms up a tad.



Normal.

The center vent opens only when the system is in full cooling mode.

In heating mode most of the air is sent to the foot well vents with a bit coming from the side vents.

In 'blend' mode the air comes from both the side vents and the foot well vents in about equal measure.

Cheers
DD

 

Thanks Doug. I am not going to mess with it. Works fine as it is.