A/C problem

"90 F150 300 CID automatic 2 WD. When driving the A/C works on max for about 15 minutes or will work on normal for about 1/2 hour then turns warm, if I shut the A/c off for about 15 minutes and turn it on it will work for the same amount of time. I ran it in the drive way on max for an hour and it worked the entire time, then switched to nomral and ran another 1/2 hour and also worked fine. The temps I got were very consistant for the 1 1/2 hours: compressor output 166, condenser output 125, evaporator output 57, interior air vent 55. Low pressure side is in normal range, however, the entire time I ran it in the driveway the compressor never shut off. It was professionally converted to 134a about 8 years ago, I've had to add I think 1 or 2 cans of 134a during the past 8 years other wise it has been working fine till now. Not knowing much about A/C, where do I start? thanks.

"90 F150 300 CID automatic 2 WD. When driving the A/C works on max for about 15 minutes or will work on normal for about 1/2 hour then turns warm, if I shut the A/c off for about 15 minutes and turn it on it will work for the same amount of time. I ran it in the drive way on max for an hour and it worked the entire time, then switched to nomral and ran another 1/2 hour and also worked fine. The temps I got were very consistant for the 1 1/2 hours: compressor output 166, condenser output 125, evaporator output 57, interior air vent 55. Low pressure side is in normal range, however, the entire time I ran it in the driveway the compressor never shut off. It was professionally converted to 134a about 8 years ago, I've had to add I think 1 or 2 cans of 134a during the past 8 years other wise it has been working fine till now. Not knowing much about A/C, where do I start? thanks.
Any work done to the AC system should really be done by a professional . It is a safety issue and is best performed by a certified mechanic with the proper tools . Otherwise you expose yourself to dangerous risks as well as risking more problems and damage to your AC system .

problem solved!!

problem solved!!

What do we win if we guess what the solution was?

when sitting in idle for an hour and a half the compressor never shut off, when driving the ram air thru the condenser cools faster than the fan does at idle so the compressor cycles more often, if the air gap on the clutch is in limits but really close to the high end it won't always have the magnetic strength to engage, I made a new spacer .015 thinner than the one that was in there and so far it has worked consistantly. I guess that must make me a professional - at least I didn't need special tools (other than my lathe) and I didn't hurt myself.
If you are having the same problem, what I did was to drive a country road until it started blowing warmer air, I pulled over imediately, popped the hood and the clutch was not engaged, I had a stick in hand (another specialized tool) ready to tap the clutch, I just touched the clutch and it engaged, telling me it was trying to engage but couldn't pull it that far.

very common problem on most any dodge, chevy or ford...good that you caught it snd figured it out- but I usually just opt to take out the entire shim- never have had to turn one down-- as long as there is clearance that is all thst is necessary.