AC Compressor running all the time?
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Elder User
Joined: Dec 2008
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From: North Carolina
AC Compressor running all the time?
I took a 300 mile trip last weekend from NJ to VA and drove straight through. It was a little cool outside, so i had the heat on through the front vents, no problem.
When i arrived at my destination, i got out, and noticed that something was dripping from the passenger side front fender area. Popped the hood to find that the AC evap line was sweating like the AC had been on. I checked it after driving it a few more times since then and the evap line is always ice cold regardless of the heater settings on the dash.
Is it supposed to be like this?
Im not sure how the compressor works (electric? mechanical? is there a thermostat that turns the compressor on and off?) so an education on super duty cooling systems would be appreciated. Is there a clutch? is something shorted or stuck? I don't want to ruin my AC by running it all winter (a costly repair i would like to avoid.)
I left the truck in VA, and won't get it back until mid december, but i would like to gather parts and knowledge so i can fix it first thing when i go down there again.
When i arrived at my destination, i got out, and noticed that something was dripping from the passenger side front fender area. Popped the hood to find that the AC evap line was sweating like the AC had been on. I checked it after driving it a few more times since then and the evap line is always ice cold regardless of the heater settings on the dash.
Is it supposed to be like this?
Im not sure how the compressor works (electric? mechanical? is there a thermostat that turns the compressor on and off?) so an education on super duty cooling systems would be appreciated. Is there a clutch? is something shorted or stuck? I don't want to ruin my AC by running it all winter (a costly repair i would like to avoid.) I left the truck in VA, and won't get it back until mid december, but i would like to gather parts and knowledge so i can fix it first thing when i go down there again.
Senior User
Joined: Jan 2002
Posts: 170
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From: Alberta, Canada
It seems to me if I recall correctly, that the only position the AC compressor does not run is in the OFF position, and the VENT position. There is an electromagnetic clutch that kicks in the compressor when required, so if you are not using the air conditioning, the compressor does not run very much. I always assumed that it was to ensure lubrication of the compressor, but that is just conjecture on my part.
Senior User
Joined: Oct 2008
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the A/C is clutch driven by a switch on your dash. the r-134a and the pag oil thats inside the system lubricate it. it cycles to keep a temperature, not to lube. if the compressor is "running" while the heat is on there is a definite malfunction within the switches, unless ford decided to do something new and go with a heat pump system in the newer trucks. any way as long as it maintains a comfortable temp. it shouldn't hurt it any. but for your peace of mind, i would seriously go get it checked out. by the way i just graduated from an hvac/r program, that way you don't think i'm just spewing usless info.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,725
Likes: 2,651
From: SE Florida
The A/C system in these trucks is designed to run the compressor in every position except OFF, VENT, and FLOOR. It isn't a heat pump system, that would be silly when the engine is producing heat that is dumped to the atmosphere.
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Joined: Feb 2006
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the A/C is clutch driven by a switch on your dash. the r-134a and the pag oil thats inside the system lubricate it. it cycles to keep a temperature, not to lube. if the compressor is "running" while the heat is on there is a definite malfunction within the switches, unless ford decided to do something new and go with a heat pump system in the newer trucks. any way as long as it maintains a comfortable temp. it shouldn't hurt it any. but for your peace of mind, i would seriously go get it checked out. by the way i just graduated from an hvac/r program, that way you don't think i'm just spewing usless info.
Close but I want to correct you on one thing. the ac in these trucks will run unless it is on the vent or floor only positions. if you have it on any other positions it will run until its cold enough outside where the computer doesnt need to engage the compressor to get the desired coolness. even if you crank it all the way to hot on a/c mode or max a/c mode the compressor will run. reason being is the air hits the a/c core first then gets heated by the heater core. by running the air through the a/c core first the car can dry up the air and heat it so you get dry hot air. benifit is on a cold rainy day having hot dry air keeps you warm and the windows very fog free!
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Elder User
Joined: Dec 2008
Posts: 745
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From: North Carolina
Thanks guys,
I did not have the AC or max AC on. I believe it was on vent the entire time.
hmmm... so i will have to expirement with it more at christmas. At least the AC works!
I did not have the AC or max AC on. I believe it was on vent the entire time.
hmmm... so i will have to expirement with it more at christmas. At least the AC works!
More Turbo
Joined: Aug 2006
Posts: 530
Likes: 2
From: W. Wisc
Yep, that's how Ford runs all their HVAC systems, to my knowledge: AC runs in all positions except Floor or Vent. The limit is the Low pressure cutout switch. When the outside temp gets too low, the pressure in the system gets low enough such that it won't close the LP switch, so the compressor won't run at that point.
Running the AC in the winter is actually a good thing as it helps distrubute the oil in the system around. Keeps seals and parts lubed that way.
Without further info on the situation that would really indicate a problem, it sounds normal to me.
-Dave
Running the AC in the winter is actually a good thing as it helps distrubute the oil in the system around. Keeps seals and parts lubed that way.
Without further info on the situation that would really indicate a problem, it sounds normal to me.
-Dave
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