AC Clutch
Lead Driver
Joined: Dec 2006
Posts: 7,092
Likes: 145
From: San Diego, CA
Your air gap might be too large for the A/C clutch.
Start here (post #3): https://www.ford-trucks.com/forums/5...ml#post4464164
Here are some more for you to peruse:
https://www.ford-trucks.com/forums/1...h-air-gap.html
https://www.ford-trucks.com/forums/1382776-air-gap.html
https://www.ford-trucks.com/forums/1...knowledge.html
https://www.ford-trucks.com/forums/1...gap-fixed.html
https://www.ford-trucks.com/forums/6...-question.html
This by no means the entire list. Plenty of us have suffered intermittent A/C issues for one reason or another. If you have a continuous cycling of the compressor, though, it is most likely the air gap for the clutch. It's a cheap fix compared to other options and worth a try IMO.
I recommend that you post your engine-related issues in the 99-03 7.3L section. Lots of people that know way too much about our trucks over there. Not all of us cruise over here in the general SD sections as our trucks are several generations old and not as relevant over here any more.
Start here (post #3): https://www.ford-trucks.com/forums/5...ml#post4464164
Here are some more for you to peruse:
https://www.ford-trucks.com/forums/1...h-air-gap.html
https://www.ford-trucks.com/forums/1382776-air-gap.html
https://www.ford-trucks.com/forums/1...knowledge.html
https://www.ford-trucks.com/forums/1...gap-fixed.html
https://www.ford-trucks.com/forums/6...-question.html
This by no means the entire list. Plenty of us have suffered intermittent A/C issues for one reason or another. If you have a continuous cycling of the compressor, though, it is most likely the air gap for the clutch. It's a cheap fix compared to other options and worth a try IMO.
I recommend that you post your engine-related issues in the 99-03 7.3L section. Lots of people that know way too much about our trucks over there. Not all of us cruise over here in the general SD sections as our trucks are several generations old and not as relevant over here any more.
Senior User
Joined: Apr 2013
Posts: 141
Likes: 0
From: Canada's Wet Coast
the 7.3L does not use a relay so maybe the function switch has continuity in the ac clutch circuit even when you have it in the off position ?
check the violet wire coming out of the function switch to see if there is 12v even when off or panel or floor. all other functions allow 12v through to the ac pressure switches
check the violet wire coming out of the function switch to see if there is 12v even when off or panel or floor. all other functions allow 12v through to the ac pressure switches
Hotshot
Joined: Jan 2004
Posts: 19,760
Likes: 1,079
From: St Louis
ac clutch is turning on and off even when the defrost or ac is off...where should I start to diagnose this?
Your description is not precise enough to determine if you even have a real malfunction.
AC compressor operation *should* be disabled when the climate control MODE switch is in the OFF, VENT (PANEL), or HEAT (only) positions. It is enabled in every other position.
AC compressor operation *should* be disabled when the climate control MODE switch is in the OFF, VENT (PANEL), or HEAT (only) positions. It is enabled in every other position.
Go double-check the exact switch positions that it is observed to be operating in.
Thread Starter
|
Tuned
Joined: Feb 2015
Posts: 258
Likes: 11
Your description is not precise enough to determine if you even have a real malfunction.
AC compressor operation *should* be disabled when the climate control MODE switch is in the OFF, VENT (PANEL), or HEAT (only) positions. It is enabled in every other position.
Go double-check the exact switch positions that it is observed to be operating in.
AC compressor operation *should* be disabled when the climate control MODE switch is in the OFF, VENT (PANEL), or HEAT (only) positions. It is enabled in every other position.
Go double-check the exact switch positions that it is observed to be operating in.
7th Gear
Joined: Oct 2005
Posts: 7
Likes: 2
I think it is only off in vent and off. My dearly departed 2002 F350 would run compressor in all but those two selections.
If it is lower 50's down to low 40's short cycling is normal. In the 30's it will run briefly and then go off for 45sec to a min or more. Once in the low 30's or colder it will not come on. The cycling is controlled by a pressure switch and the gas pressure gets lower with temp and will reach a point where pressure is not high enough to ever close the switch and operate clutch. Clutch gap being wide causes compressor to work OK and then after a few minutes the winding gets warm from current flow and conducted heat and current flow drops and that makes magnetic field too weak to pull clutch together given the wider gap and higher magnet requirement. Cutting off compressor for a bit lets winding cool and you get another few minutes of use before it happens again.
If it is lower 50's down to low 40's short cycling is normal. In the 30's it will run briefly and then go off for 45sec to a min or more. Once in the low 30's or colder it will not come on. The cycling is controlled by a pressure switch and the gas pressure gets lower with temp and will reach a point where pressure is not high enough to ever close the switch and operate clutch. Clutch gap being wide causes compressor to work OK and then after a few minutes the winding gets warm from current flow and conducted heat and current flow drops and that makes magnetic field too weak to pull clutch together given the wider gap and higher magnet requirement. Cutting off compressor for a bit lets winding cool and you get another few minutes of use before it happens again.
Trending Topics
Hotshot
Joined: Jan 2004
Posts: 19,760
Likes: 1,079
From: St Louis
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Hotshot
Joined: Jan 2004
Posts: 19,760
Likes: 1,079
From: St Louis
If its cool enough outside then it's normal to have very short cycling, it any engagement at all. If it's above 50°F, the cycling rate should get longer as the temperature rises and the load on the system increases. If the temp is high enough where you NEED A/C performance, then short-cycling is a concern.
Start by reading the HVAC FAQs, the link is in my signature.
7th Gear
Joined: Oct 2005
Posts: 7
Likes: 2
With a CCOT system the pressure cycling switch for compressor goes open at 24 psi and closes at 42 psi (a couple of psi range to those numbers but open number can't be less than 21 psi without risk of evaporator freezing in higher humdity with low fan speed). When it is in the lower 50s and below, the pressure will drop very rapidly from the 42 close pressure back to the 24 open pressure just like when the system is low on refrigerant at temps 30 degrees or so higher.
Hotshot
Joined: Jan 2004
Posts: 19,760
Likes: 1,079
From: St Louis
There is no getting around that behavior.
Thread Starter
|
Tuned
Joined: Feb 2015
Posts: 258
Likes: 11
Maybe, maybe not. You haven't provided enough pertinent information to determine that. THAT behavior is not what you asked about in the first place.
If its cool enough outside then it's normal to have very short cycling, it any engagement at all. If it's above 50°F, the cycling rate should get longer as the temperature rises and the load on the system increases. If the temp is high enough where you NEED A/C performance, then short-cycling is a concern.
Start by reading the HVAC FAQs, the link is in my signature.
If its cool enough outside then it's normal to have very short cycling, it any engagement at all. If it's above 50°F, the cycling rate should get longer as the temperature rises and the load on the system increases. If the temp is high enough where you NEED A/C performance, then short-cycling is a concern.
Start by reading the HVAC FAQs, the link is in my signature.