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?

Have you checked your A/C compressor air gap? Sounds like that is your problem.

I think another issue these trucks have is the blend door not opening or closing fully due to a vacume issue or a broken blend door.

would it be expected that the comp. clutch could engage to begin with and then drop out after running 5-10 mins?

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.

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.

Yes. The link I posted explains why and how to fix it yourself. I don't know that it is your problem, but it is pretty easy to check with a feeler gauge. :-X22

"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."

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.

If you could, post up some results of the repair. I've got the same problem, and it's quickly rising to the top of the "to do list" as the weather is warming up.

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.

Looking forward to hearing if this cures the problem.

By the way, I really hope your name is P. Prash. ;)

FYI, It was the clutch air gap. Worrked perfec today. Very easy to do. Note the little washers want to stay on the comp shaft too as it has magnetism.

Thanks for the update.

So what was the gap when you started?

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.