Searched all through this forum looking for a good solution to this. Had this truck for more than five years I believe so I know refrigerant hasn't been added so its not a overcharge situation.

I do HVAC for a living so I know what I'm doing with gauges. Here are the symptoms

Sitting at idle truck cools perfectly like expected. Pull on to road and things go sideways. Above let's say 1200 rpms discharge temp sux. I did the mod with a valve in the heater hose couple years back for the Max Cool so it's not a hot heater core deal.
Today I did the air-gap check with intentions to pull a shim, no Bueno, only one shim in my clutch. I tested at .38 to start and minus the washer / shim I end up at .08 so I left the washer in and ordered a kit.

I hooked up my gauges and had the wife throttle up the truck to 1500 rpms and I could actually see what the compressor is doing. Appears to me the I may have a high pressure switch going south as it the clutch is engaging and disengaging rapidly, maybe on for 8-10 seconds then off for about 5.

My pressures when it's running looks good to me at 40-45 psi on suction and high side was 90 - 100. My ambient at the time was maybe 80.

Just tossing this out there to see if any others had a similar issue. After I do the air gap correction if it doesn't improve I'll move on to try the high pressure switch. I'll post my findings.

 

Looks like your high side is reading low

 

Looks like you are right, I must have not have remembered the high side right. Next time I test I'll write them down so I'll have the correct readings.

 

I had something similar. Removed the spacer in the a/c clutch, has worked since then. I don't have the instructions, but remember it looked like a small washer. I think it was intended to be removed after a certain amount of wear on the clutch. Someting to consider.

 

Same problem would Like to know the fix

 

90-100 on high side is low. At 80 you should be seeing closer to 150. Suspect charge is low.
Evacuate, measure, pressure test, fix leak, vacuum (I like 30-45 minutes) and recharge.

 

On both 7.3's I have owned I had this sort of problem. On both trucks, we finally found out the plug, from the compressor to the switch.... was shorting out. You could wiggle the plug wires and compressor would turn on or off....

I faulted myself, as when working on engines I would lay of top of that plug a lot of times over the years.

 

Had time to try again today. Shim kit came in, got the air gap around .31. Hooked gauges up again and see where I goofed last time, was looking at R-22 temp scale instead of pressure on high side.

Pressures today were 35-40 suction and 175 discharge. Had wife throttle up again after cab was cold as soon as she hit the peddle the compressor starts cycling. I went so far as to disconnect high side pressure switch and jumper it, no joy still cycles.

Odd, as high side never gets above 190ish.

My Chilton book show a "Air Conditioning pressure cycling switch" on the accumulator but doesn't say what the pressure it cycles at.

 

I’m not sure what the high pressure cutout is, but the low side cuts out at 23psi on my gauges. I had issues with the low pressure side recently and ended up replacing the orifice with a variable one. The old one was plugged with debris. This is the 2nd time I’ve found debris in the orifice screen despite replacing compressor, accumulator, condenser, hoses and flushed the evap.

 

Here you go.

 

Thank you sir!

 

Just an update, rookie mistake. I didn’t take all symptoms into account. Blew the charge and put back correct charge all is good now. Was cycling on low pressure. I was reading into it’s cooling when at low idle to not consider a small leak over time, this not cooling at high RPM began couple years back but we mainly use this truck in fall and spring to pull 5er. Appreciate all the suggestions I got.