I just ran into this problem but I'm pretty sure I know what happen in my case. What had happened was I made a trip to town and put my truck back in the shop and closed the door. Wasn't but a short time later I get a call to do firewood hauling. I pulled the truck out and set the A/C for MAX A/C and proceeded on hitching up the trailer. I start noticing the compressor pulling really hard on the engine and cycling rapidly. Thought that was odd I got back in the truck the vents were blow warm air. Compressor still cycling. Then I head the compressor struggle and then started venting freon. I knew then what was going on I shut down the A/C and left it off till I was rolling. I did open the hood and look and the fan was FULLY UNLOCK and barely turning. So what has happen the freon was preheated and pressure were to high and kicking out on the high side pressures till it got so high it was venting to protect the system (around 450 PSI).

 

After I was on my way and got coolant up to temp and the fan was partial locked now the A/C worked just fine the rest of the day. So now experiencing this and seeing post in the past about warm A/C at stops I wonder if the fan is not properly locking and keeping air moving and the high side is shutting it down. Another possible occurrence is using Quickie Can with the hose included those typically have a oil charge with them and it possible to over charge with too much oil causing that problem. I've seen where condenser coils are so packed with bugs that air doesn't flow and freon temperatures and pressure sky rocket.

 

Like today I took the time and fired up the pressure washer and slowly worked my way across the condenser, intercooler and radiator being careful not to get to close to the coolers.Today again it reached a 100*F here at my house. So keeping radiators, intercoolers and condensers cleaned is priority. So if your fan clutch is not locking properly to keep air flow moving the condenser will for sure get too hot and drive the high side pressure to trip the high side switch. So think air flow when the A/C is getting warm at stops.

If you come up with an alternative or fix, I would be interested.  I haven't found one yet.  All I've done that somewhat helps is to run 6cyl high idle.

Edited July 21, 20159 yr by CSM

About 20 years ago fords used a electric fan in front of the condenser and the stock belt driven fan on the motor. As I recall the electric fan had no shroud and only came on when the A.C. was on to solve the very same problem.

Sounds like it's time for a 3rd gen fan clutch with a switch in the cab...

I've found low freon to cause the exat issues you have described as well.

Different issue. Low freon is at the other side of the spectrum. As freon pressures drop on the lo side the the temperature continues to drop below freezing point which the lo side switch cut off the compressor. The lo side switch is designed to prevent freeze up of the evaporator. So you need to add freon to bring the lo side pressure above 30 PSI typically charge to 35-40 PSI to get a solid locked compressor and a system that is sweating. Typically with lo freon you'll also see low hi side pressures as well like 100-120 PSI which isn't enough pressure to work the orifice tube. About 200-250 PSI is about optimal for our trucks depending on temperatures of course.

 

But to be bumping the high side switch is because you heated all the freon above normal like in my case in a hot shop, door closed and hot engine warming everything up. Then start the truck and have a unlocked fan and pumping freon till it overheats and no longer can stay with hi side limits and start venting. (>450 PSI).

You didn't address my top comment.....

Will 3rd gen fan bolt up?

Fan? No. Won't fit in our shroud. Fan clutch? Maybe... I need to look into it.

Would surprise me if someone hasn't tried it

Bad news... 3rd gen spins the other direction, so the threads would be backwards.

So you would have to replace the complete fan hub assembly mount???

No. The direction the belt travels. So you would have to figure out a new belt direction and then also most likely have problems with the water pump.

It's a lost cause....