Can someone confirm AC should RUN in defrost mode

[Brad Murray]

I have a 2010 Sport Trac which does a very poor job defogging the windshield (must run at full hot and full fan for 20-30 minutes). Dealer says no trouble found but I noticed the AC compressor does not turn on when system is in defrost mode (even when temp is set to cold). I recall the AC is used to dehumidify the air in defrost mode. Can someone confirm this for me?

 

[Rodger Tellefson]

I have read here that this is true.

 

[MikeSondra Grossen]

Yes, our AC kicks on for defrost mode...we can hear the compressor engage.

 

[Jim parnell]

I believe the only time the compressor does not cycle is in the vent and floor positions, all others the compressor cycles unless they changed it in your model year.

 

[Steve McKellop]

You didn't say whether you had the manual climate control but the operationof the compressor would be the same,the controls different.



From the Ford Service Manual:

Manual Climate Control System



The manual climate control system operation is determined by the settings on the climate control assembly. The climate control assembly includes a serviceable function selector switch and blower motor switch. The temperature control switch, A/C request switch and rear window defrost switch are integral to the climate control assembly and are serviced as an assembly.



The blower motor switch:

sets the front blower motor speed.

directs the blower motor path to ground through the blower motor resistor to allow blower motor operation in LO, MED-LO and MED-HI.

actuates the high speed blower motor relay, giving the blower motor a direct path to ground which allows the blower motor to operate in HI.



The temperature control switch:

is a potentiometer that outputs a variable voltage to the temperature blend door actuator to set the position of the temperature blend door.

initiates closing of the heater control valve. When set to full COOL, a lever on the temperature blend door pivot shaft depresses the pintle of the heater control valve vacuum switch. The heater control valve vacuum switch then applies vacuum to the heater control valve, closing off engine coolant flow to the heater core.

is serviced only with the climate control assembly.



The function selector switch setting:

determines where the system airflow is directed.

enables blower motor operation.

enables auxiliary blower motor operation, if equipped, by supplying voltage to the auxiliary blower motor relay.

commands A/C compressor operation in MAX A/C, FLOOR/DEFROST and DEFROST.



The A/C request switch:

can command the A/C compressor on when the function selector switch is in PANEL, FLOOR/PANEL and FLOOR when the A/C request switch is pressed.

is inoperative in MAX A/C, OFF, FLOOR/DEFROST and DEFROST.

indicator illuminates when the function selector switch is in MAX A/C and cannot be toggled.

indicator does not illuminate in OFF and cannot be toggled.

indicator does not illuminate in FLOOR/DEFROST and DEFROST and cannot be toggled. The A/C compressor will not operate if the outside air temperature is below -1C (30F). The A/C compressor will resume operation when the outside air temperature rises above 2C (35F).

is serviced only with the climate control assembly.

 

[Brad Murray]

Many thanks to all and especially to Steve M for the excerpt from the manual. Since I'm currently below the 30F level, the AC in defrost should not operate. Should the AC operate in MAX AC mode at temperatures below 30F? My compressor does not operate in any mode but I'm below 30F. How can I verify the AC compressor is working properly in these temperatures?

 

[David Ponder]

Brad, Put it in the garage and check it as you drive it out the next morning. Otherwise, somewhere heated like a local auto shop to park inside for a while to warm up...



Does it cycle at all after the engine compartment is fully warmed up?

 

[Gavin Allan]

You should not need AC compressor running below 30 degrees. If you are having moisture problems, perhaps you have a water leak getting water into your Trac, or maybe the heater core is leaking.



Another main cause of moisture problems: runing in "Recirculate" mode in cold temperature. You should have it set to "Fresh" air mode, not recirculate.

 

[Rob Allen]

This also answers my question I had a few weeks ago about hearing a relay tripping when I set the blower speed to HI. Thanks!

 

[Brad Murray]

At the dealer again. Still no trouble found but they are keeping it overnight to duplicate the problem. I'll keep this thread updated.