Until this morning when I adjusted the AC clutch air gap, my truck's AC was mediocre at best when it cooled at all. It was relatively cool until the engine got up to operating temp, and then it would randomly get warm, and eventually it would get cool again. Low rpm's always caused it to get warm faster.

Since I did the air gap mod, it gets very cold and stays cold as long as the truck is moving. At stop lights I notice a subtle rise in temp that reverses as soon as I hit the gas pedal; not much change in comfort level. It did get warm and clammy sitting in a parking lot eating lunch.

When I got home I put the gauges on it without shutting down the engine and here's what I got at idle: Low-pressure 27psi, high-pressure 180psi. This at roughly 85 degrees ambient temps.

Is this simply a low charge issue? Old compressor not working efficiently? Bad radiator fan clutch?

I imagine the answer is really obvious to anyone with a thorough understanding of AC systems. Thanks in advance for any advice!

 

Also, on the way home I noticed a droning sound coming from the vents. It was very subtle on AC with the fan on level 3, definitely noticeable with the fan on high, and almost nauseating on MAX AC with the fan on high. I wonder if this is the recirculate door not closing/opening completely.

 

That's normal since the compressor doesn't turn as fast at idle and there is no forward motion to force air through the condenser.

 

Maybe subtle is the wrong word. If I sit at a light long enough it starts getting warmer than it should. Kind of like sitting in a parking lot long enough that there is no cold air. I've owned enough cars in my life that I know it's not normal.

 

Have you taken a look under the hood at the compressor and the fan during these warmer air times to see if they're turning or not?

 

85 ambient temp should be closer to 45-55 psi low and 225-250 psi high.
BUT cold while moving and warm/hot when sitting then get cold again as soon as you start moving is a classic sign of a bad fan clutch.

 

No, but I will next time. Today was much cooler than yesterday so no dice.

 

My ECT at idle is 192. If it was a fan clutch wouldn't that be higher?

The clutch was new two years ago when I converted it to a 7.3L manual clutch. Maybe I'll put the stock electronic clutch back in and see if it makes a difference. At the very least I'll have two fewer recurring trouble codes.

 

coolant temps vary by location. i ran my 02 7.3 for two years with no fan at all and had no issues unless sitting idling for over 5 minutes. then once moving again it would cool rite back down as soon as i started moving.

 

My location is Texas. We've already had mid 90 temps. I changed my thermostat three weeks ago because ECT at idle was below factory @186. I don't think its the fan clutch, but I'm going to switch it out just to satisfy my curiosity. I may charge the ac system before going through the trouble though.

 

Get the gauges hooked up with the truck in your driveway. Insert a thermometer into the center vent. Record pressures and temp while output is still comfortable. Run it at idle until you notice the outlet temperature no longer maintaining a comfortable temp. Record pressures and temp again. Grab your garden hose and spray the condenser with cold water for a minute. Report resulting pressure and temperature behavior.

 

Since starting this thread, I haven't been able to reproduce the failure. I let the truck idle in the driveway for 30 minutes with 85deg outside temps and the air in the cab never got above 50deg. I guess we'll see what happens when we hit the 100s down here.

 

Self-healing vehicles...gotta love 'em.

 

LOL. I'll love it if it doesn't decide to relapse when I'm on a road trip.

 

First thing I did on my 93 7.3 F250 was change the FOT to a VOV it has truly solved many issues in the Ford AC system.