AC works for 5-10 mins then gets warm
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Mountain Pass
Joined: Feb 2006
Posts: 132
Likes: 4
AC works for 5-10 mins then gets warm
I bought a 99 F350 over the winter. Turned on the AC for first time yesterday as it hit 90. It would cool well for 5-10 mins then the air would get warm. If I turned the fan down it would get cold again. If I turned up the fan it would all of the subben be warm again in 5 mins. Is this a sign it is low on freon?
Cargo Master
Joined: Sep 2007
Posts: 2,624
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From: OR and UT
Beer Fridge Finder
Joined: Apr 2003
Posts: 14,988
Likes: 1,151
From: Savannah, GA
My compressor cycles on and off, it's normal. I did have the warm air problem too - it was the blend door as mentioned above. The vacuum pump on the passenger side fender decided to stop working. I think it was like $30 at NAPA.
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Mountain Pass
Joined: Feb 2006
Posts: 132
Likes: 4
is there an easy way to diagnose the blend door? It seems like I looked and that was not vacuum but stepper motor driven a few years ago when I put a heater core in? I will do some searching, thanks for the push.
Cargo Master
Joined: Sep 2007
Posts: 2,624
Likes: 6
From: OR and UT
"Like any device with clutch plates, they eventually wear. In this case, the "air gap" wears wider. Eventually, the air gap becomes so wide that the electro-magnetic coil that pulls in the clutch plate can no longer do its job, and the air conditioning compressor (Ford FS-10) no longer comes on, resulting in no cold air.
In reality, before it completely fails, the clutch becomes intermittent, and you get cold air sometimes, and sometimes not. Usually it works upon initial turn-on for a couple of minutes, then loses the ability. I suspect this is due to the difference in magnetism with slightly different amounts of current passing through the magnet's coil. Cold wire has lower resistance, thus it's easier for current to pass, thus more current, and more magnetism to overcome the greater air gap."
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Mountain Pass
Joined: Feb 2006
Posts: 132
Likes: 4
yea, my issues look to be clutch related. it started getting warm so I pulled over. Comp. wa not running. I tapped it with a flashlight and it kicked in. So, I will check gap tonight. I printed instruction and plan to look at it.
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Thread Starter
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Mountain Pass
Joined: Feb 2006
Posts: 132
Likes: 4
I took the AC clutch disk off last night and removed 1 washer & put it back on. Much closer gap now with no noise at idle with AC off. I will test today and report back. I assume it will help.
Fleet Mechanic
Joined: Mar 2010
Posts: 1,342
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From: Jamestown, IN
So what was the gap when you started?
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Mountain Pass
Joined: Feb 2006
Posts: 132
Likes: 4
no idea. It took about 45 seconds to get the clutch off. I removed 1 of the 2 washers, put it back on, been working perfect. I just got home from a 500 mile trip pulling boat from weekend. AC was ice cold.