I've been scouring the Internet trying to find info on a unique problem like mine, but haven't found anything exactly like this so far.
I have a 2003 Ram 1500 Quad. 4.7, 5spd auto, 90,000 mi. I've been having a problem with my A/C, but only on HOT days. On cooler days the A/C works fine and blows ice cold air all day. If the truck is allowed to sit in the sun on a day where the temp is over say 80deg and the interior gets really warm, the A/C will not work. I normally leave the A/C switch on all the time and don't change the settings except to add a little heat if it gets too cold.
Here's an example of my ongoing problem: I live near Seattle so the weather has been pretty nice. Yesterday the temps were in the mid to upper 60's maybe touching 70 in the afternoon, When it's cooler like this I have no problems. I started the truck in the morning and A/C was blowing cold, Had a lot of errands to run so I was driving around town all day stopping at a number of different locations. Every time I started the truck the A/C worked just fine.
Today was a different story, the weather was warmer into the 80's. The truck was sitting in the sun all day and by the time I needed to use it in late afternoon, it was pretty warm inside. I started the truck up and no cold air. Cycled the switch, stopped and re-started the engine, nothing worked.
The light on the A/C switch is lit when on, goes out when off. I've checked under the hood each time and when the A/C isn't working, the clutch is not engaged. Tried tapping on the clutch but no luck. Remember, this only happens if the truck has been sitting in the hot sun. I'll go out tomorrow morning when it's cool, and start it up, the A/C will work just fine and continue to operate even if the weather heats up. Turning the A/C switch on and off makes no difference. If it's a day when it's working, it continues to work, on a day when it is not, cycling the switch does not help.
I'm at my wit's end. Hoping someone here can give me some ideas on what to check/do next. Our hot weather usually starts this month and runs thru September so I'd really like to get this fixed.

 

Its very possible you have a weak condenser fan. This has been seen numerous times in the past, the fan gets weak and doesn't turn as fast or not at all. Start the engine and turn on the a/c, check the fan operation. It is also possible that you could be slightly low on charge, but the only "correct" way to check this is pulling the charge out with a recovery machine and weighing it. Don't go to the auto store, get a can of 134a and shoot a topper into the system, it may not need it, then you'd be overcharged-----just as bad or worse than undercharged.

 

Thanks Gone Fishin
, I'll check out the fan. As for the charge could it be low if it's ice cold one day and nothing the next? Also could the low charge stop the clutch from engaging?

Thanks again!

 

I agree that it's likely the fan, and also check the A/C relay. Do you hear it click when you turn on the A/C?
On days the air is ice cold, was that when you were moving or on the highway? You forward speed may have cooled the condenser enough to give cold air.

 

OK, Checked this morning and since it was cool, the A/C worked fine. Clutch was engaged, and the condenser fan was blowing. I'll check this afternoon after it warms up but since the forecast says we'll only get up to 75deg today, I'm not sure if it will be hot enough to cause it to stop working. Was blowing cold just sitting in the driveway at idle.

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Wednesday was cooler only in the high 70's but when I got into the truck the cab was hot from the sun. The A/C didn't work. Checked the condenser fan and it was not blowing. When I got to my destination, I parked in the shade. Came back in about an hour and the truck was cool and the A/C was working again. Checked and the condenser fan was blowing. Yesterday was warmer, into the 80's and the A/C would not work, but this morning before it got hot I started the truck in the driveway and the A/C was blowing Cold, by afternoon, the truck cab was warm again and the A/C quit working.
I did find that when it's hot enough to cause the problem, the condenser fan is not working, but that fan works when it's cool. Another thing is, if I start out driving when it's cool the A/C will work, and as long as I keep the truck running the A/C will keep blowing ice cold even if it gets hot outside. Seems that the cab of the truck has to be hot to cause the problem, as long as I keep the cab cool I have A/C. Any ideas?

 

Not sure but Im guessing the condensor fan has a relay. When its not working try swapping out this relay for another known good one ?

 

Thanks TrueDogman
, I'll give it a try, ...have to do some research to see where it's located