Why the Thermostat in the A/C Box

[holanae]

Does anybody know why dodge installed a thermostat sensor in the A/C box with a wire coming off the back off the heater control valve?  A few people told me it is fine without the thermostat connected. The temperature is manually controlled, so why the thermostat?  Is it used to prevent freeze over by automatically opening the heater control valve when needed to defrost the evap core?

[68-XS29]

If the sensor is in the A/C evaporator, then I believe it will cycle the A/C compressor off when it gets too cold to prevent freeze up.

[holanae]

But it is only wired to the back of the heater control valve on the firewall.

I guess what I am getting at is, can I truly run without the thermostat line?

[cdr]

But it is only wired to the back of the heater control valve on the firewall.

I guess what I am getting at is, can I truly run without the thermostat line?

it works without it, I put a clutch cycling switch on mine

[Bronzedodge]

Yes, it only affects the travel of the valve slightly.  I have spoken to the valve rebuilders (heatercontrolvalve.com, heatervalves.net and OldAirProducts) and no one that I know of restores the capillary tube (fig 8 on 24-11  or it's operation.  I'm not even sure of the charge - could be alcohol, could be refrigerant.

The FSM is sketchy on the details, but in the 69 book on page 24-11, under 'Water Valve Test"

..."The sensing unit is located at the lower right-hand corner of the air conditioning housing.
   Remove the radiator cap to minimize pressure in the car's cooling system.  Move the temperature control slide lever on the instrument panel to the extreme "Warm" position then back to the "Off" position.
   Push the "Max A/C" button in, and with the blower in the "Low" position, run the air conditioning system for five minutes, then test the water valve by momentarily disconnecting the heater outlet hose at the upper side of the heater.   ...'

[John_Kunkel]

Not Mopar but explains it:

http://www.sw-em.com/Heater_Control_Valve.htm

"Function of the Thermal feedback for closed loop control:  A capillary sensing tube is positioned in the Heater Core housing, in the airstream on the downstream side of the Heater Core, and in this manner senses the air temperature after it has warmed by the Heater Core.  An expansion bulb located on the other end of the capillary tube in the HCV mechanism, adds this (minimal) Thermal Sensing input into the (driver-set) Mechanical Setting, to maintain a constant temperature".