a/c malady
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a/c malady
so, we're driving along 'bout 70 mph in my '01 5.4 f250 and the a/c stops working from disengaged clutch. was cooling nicely. clutch air gap is good. jumpered low press switch-no help. cannot find hi press switch to save my life! checked fuse and relay-good. here's the kicker-when first energized, clutch will engage for about 20 secs and starts cooling. then it kicks out and will not re-engage until engine is turned off and back on again. you can even cycle the key quickly w/o killing the engine and it will re-engage for about 20 secs before kicking out again! clutch will not engage with key on/engine off, either. can someone point a finger to something that would aid me w/this jumbled mess?
Fleet Mechanic
Joined: Sep 2013
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usually your symptoms would indicate low refrigerant. Weather you had a compressor shaft seal go out or other component fail. You won't know workout putting a Guage setup on it To see how the system is working. You can do the old add a can of r134a with leak detector in it and use the uv light to see a leak. But if you don't have a leak amd overcharge the system that is not helping you either.
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have the gages to check the system, just haven't put them on yet. don't think i've lost charge; when the clutch is engaged-only about 20 secs at most-i can feel the line getting ice cold on top of the receiver. and air start to cool down inside. why won't clutch engage w/key on-engine off? shouldn't it stay engaged w/jumpered lp switch? and where is the high press switch? sorry, don't mean to rant-and forgot to thank you for posting. at this point i'm thinking pcm; this truck has a clutch fuse and relay.
Fleet Mechanic
Joined: Sep 2013
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I don't know enough about the system to answer your ? About a high psi switch. usually there is a switch on one of the lines and one on the evaporator? The tank looking thing near the firewall. A wiring issue if you have a bad ground strap to the engine if you have power you have to make sure you have a ground to compete the circuit. I've notheard of an a/c clutch just failing but i guess anything is possible. I did have a jeep easy back that had a switch on the evaporator core itself that went bad it was some kind of thermostat but i don't know if all a/c setups have that it was an 87' cherokee.
Hotshot
Joined: Jan 2004
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From: St Louis
Put the gauges on it. You NEED to see what the system is doing and the pressure readings will provide that information.
No, they don't, not at all. Something else is going on. The gauge readings will help point in the right direction.
Because the computer controls the clutch and the guy who programmed the computer was smart enough to know that engaging the clutch when the engine wasn't running is a pointless exercise.
No, that is only one input in the chain.
On the high pressure line between the compressor and the condenser.
usually your symptoms would indicate low refrigerant.
why won't clutch engage w/key on-engine off?
shouldn't it stay engaged w/jumpered lp switch?
and where is the high press switch?
Hotshot
Joined: Jan 2004
Posts: 19,768
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From: St Louis
If the truck has a "dead miss", FIX IT! It's going to cause more issues than anything to do with the A/C system which I've never seen or heard of.
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i do appreciate your posting: you seem to know far more about this truck than i do. and i am in the process of evaluating and remedying the miss i have. 'twas a simple question. would a dead miss keep the a/c clutch from engaging? these two problems seem to have appeared at the same time. i have searched hi and low (no pun intended) for the hp switch in the line from the compressor to the condensor, and i don't see it. once again, i am in your debt for any knowledge you might infer. i'm no novice to automotive a/c repair; just not w/a pcm in the equation. thank you.
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now to close out this thread-break in one wire leading to #5 cop. fixed (soldered) and no more miss. a/c clutch engages and truck cools just fine now. still no sign of a/c hp switch. would still like to know if this system has one and precisely where it may be. and it would seem the pcm controlled clutch will not engage when the truck has a dead miss. fyi.
Fleet Mechanic
Joined: Nov 2011
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From: Land of Taxes
I just Googled 2001 F250 cooling system schematic and in the "images" tab it brought it all up. Or ask the dealer or a reputable garage to point out the Hi side fitting (edit; switch not fitting). It has to be there.
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thank you for that, sir. just went and found it. kinda disguised way down there. best place for it as close to discharge valves as possible, i guess. it may be worth adding non-operable a/c clutch w/a miss to the hvac faq's. i never would have guessed one had anything to do w/ the other????
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