I just brought home an 04 F350. It is a V10, 6 speed, with 30,600 verified miles on it. It runs and drives fantastic, and that V10 is impressive! I am very impressed.
I have noticed that the compressor cycles, even with the dial in the off position. Is this normal for the super duty, or is something amiss? If something is wrong, what direction do I look in?
Mark

 

The compressor should not be running/cycling when the switch is turned off.

I am not an A/C expert so can't really help you with where to look other than to check for any unplugged vaccum lines, electrical plugs and etc. There is a clutch in the pulley that drives the compressor, maybe your clutch is not disengaging or the a/c clutch cycling switch is bad. Hopefully someone with more experience with A/C system function can help you troubleshoot.

 

Your condition is not normal. The compressor should be enabled only in the two modes for A/C and for the two modes that defrost. It should be disabled in all other selector positions.

On your truck, the PCM is involved in the control of the compressor clutch so there's a greater level of complexity. However, it's not a vacuum problem, nor is it a cycling switch problem.

Put the selector switch i the OFF position. Pull the clutch relay and see if it disengages. If it doesn't the clutch, is mechanically jammed. Reinstall the relay. Unplug the cycling switch. If the clutch disengages, there is a problem at or near the mode selector in that it's passing power when it shouldn't, probably a bad switch or a wiring fault. If it doesn't disengage, there's a problem with the PCM and the clutch relay that needs further diagnosis.

 

If it were an issue with the PCM, would it throw a code? No CIL right now, but I will scan it to see if there are any stored codes.
It is possible that the clutch is stuck, but I doubt it's that simple. The truck has 30,000 miles on it in 10 years, so it has been sitting some.
In it's current state, do I understand things correctly that it isn't hurting it, other than wear and tear?

On a side note, I can not get over how well the V10 pulls through that 6 speed! 4.30 gears definitely do it justice.

 

all great advice, with only one minor correction.

the A/C will run in all but two positions. when "vent only" and "floor only" are selected, the A/C will not run. all other positions (except off) will engage the A/C including the "vent+floor" position (which i never understood).

awesome advice!

to the OP -- welcome to the club! our 04 also has only 30k on it and unfortunately the A/C is also giving problems. i think sometimes sitting too much is worse on some stuff than driving the heck out of them.

 

I crawled under it, and checked out the compressor clutch. It spins freely. I also turned the ignition to the run position, and it spun freely. So, it is engaging when the engine is running. The dial is in the off position.

 

Another misunderstanding of the so called "check engine" light. The "check engine" light comes on when an emission related fault is detected. It WILL NOT detect low oil pressure, low coolant level, low alternator output, or anything else that does not effect the emissions monitor. On the other hand, the PCM monitors and stores a lot of DTCs for a lot of reasons which are useful for diagnosing problems, but ONLY emissions related issues cause the "check engine" light to come on. It really should have been called something like "Emissions Malfunction Light" instead of Engine Malfunction Light.

 

That's how it's supposed to work. it isn't supposed to energize when the engine is off.

That should eliminate the possibility of the clutch being mechanically jammed.

No.

 

I'm still trying to figure out why the compressor/a-c runs on vent+floor also. The manual says it's simply the same as vent only, but air flow thru both vent systems? Not the case. I use that mode for a/c more then the actual a/c or max a/c modes.

Back to OP. Does the system cool properly when on or does it cycle too much to determine?

Also, just a thought...do you have an aftermarket air bag system someone put on that has a compressor, similar to Fords version, which cycles on and off such as in the Expy's? It might be mistaken as the a/c compressor.

The last thing just to be sure...is your interpretation of "off" only in the "O" position as the vent/air issue, noted above is a bit confusing, one click from off to the right.

 

Did you check your underhood fuse box, there is a diode in there for the a/c clutch, check your owners manual, if some one removed the diode or its popped it will cause a constant cycling compressor.

 

The diode should have nothing to do with this issue. It's there for the suppression of the spike when the clutch de-energizes.

 

Wow- enlightenment for the day.
I crawled back under the truck to watch the compressor while the engine was running but the setting was in the off position. The compressor wasn't engaged, and it did not come on. I did hear the click (of the compressor), but I sheepishly report that it was exhaust system expansion/creaking in the engine area- not the compressor clicking on and off. One mystery solved.

 

Thanks for reporting back. Some might just go away after realizing it's an embarrassing answer.

Mom regularly reminded us growing up..."honesty is always the right answer."

No stupid questions here. Thx again.

 

Lol!

Crap, your question made me go study diagrams. Now my whole weekend is ruined!!! Eeek!!!