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AC not cycling off then no air?

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Old 08-24-2017, 12:41 PM
natedog37 natedog37 is offline
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AC not cycling off then no air?

OK, an other AC question. I recently put a new clutch on (after living without AC for a year and a half!) and now the AC is on, it just doesn't cycle off and after a while the air stops blowing. I assuming this is from the coils freezing over and icing up not letting air by? What do I need to check to get it to cycle off? Thanks.
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Old 08-24-2017, 04:39 PM
SteveH-CO SteveH-CO is offline
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when you say after a while the air stops blowing - what do you mean? the fan stops? the air gets warm? the air feels warm-ish and humid (like it has iced over)?

My compressor seems reluctant to cycle (when I feel it should). I replaced the clutch cycling switch, and it did not increase compressor cycling. Mine works well enough for now, but I'll be watching it closely on the next long trip. There is another thread here recently discussing compressor cycling, and if I find it, I'll link to it.
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Old 08-24-2017, 06:08 PM
natedog37 natedog37 is offline
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I mean it stops moving air all together. I can here the fan going, but no air at all is coming out of the vents. I noticed this on a road trip, so an hour or so. So there is a compressor cycling switch? maybe thats the problem, where is it? What I think is happening is that the AC is always on and its freezing up in the passage that the air goes through and blocking the air. If I stop driving for a long period the AC will work again.
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Old 08-24-2017, 06:16 PM
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Not an A/C tech, but.... check if clutch on compressor is working at all. You may need to add a spacer... to keep it disengaged when not turned on.

Clutch cycling switch may be bad, if its not turning off compressor. Thinking if you unplug connector coming off compressor, it should stop working. If it does release the clutch, then I'd assume the compressor clutch is working correctly.

Freon level correct ?

Steven... on both my 1995 & 2001.... the pigtail from compressor failed like 4-5 times. I figured that out when I realized I could shake the wires, and compressor would engage. Replace the pigtail.

I figured I was quilty of laying on top of that connector whenever I worked on top of engine. Regardless... over the 20 years with a 7.3 engine,... it was always that connector that was at fault when compressor was intermittent.

Just my thoughts.... like I said, just my experience over 20 years
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Old 08-24-2017, 06:28 PM
natedog37 natedog37 is offline
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OK, so i just checked the wire harness on the compressor, it passed the wiggle test, nothing happened. However the compressor is running with the selector switch in the off position. I unplugged the switch and the clutch let go. I repeated that a couple of times and it let go every time, so I would assume the gap is OK? So this leaves the pigtail or cycle switch right?
I just had charged up, so I don't think its that.
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Old 08-24-2017, 06:31 PM
The Brad The Brad is offline
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When the air stops blowing, does it blow out of the defrost vents?
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Old 08-24-2017, 06:32 PM
natedog37 natedog37 is offline
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To clarify: the switch was in the OFF position when I tested the pigtail. The clutch engaged every time it was plugged in.
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Old 08-24-2017, 06:34 PM
natedog37 natedog37 is offline
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When the air stops blowing, does it blow out of the defrost vents?
No, it won't blow out of anywhere. I tried all of the positions.
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Old 08-24-2017, 06:53 PM
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If the compressor is running non stop the evap is probably freezing up. If the compressor stays engaged even with the dash selector turned off I would be checking the wiring. I do not know if the signal to the compressor clutch on our trucks is a ground signal but if it is then it's a pretty good bet the signal wire is pinched and shorted to ground. This actually happened on my Mercedes diesel, the wire got pinched during a compressor changeout and it would run with the dash selector turned off.
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Old 08-24-2017, 07:15 PM
pirschwagon pirschwagon is offline
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Check the Static Pressure vs Ambient Air Temperature to determine you have approximately the correct amount R134a in the system to ensure there is not a slow leak. This will cause freeze-up of the Evaporator Core and the system will not cycle properly. I only list this because its the most common cause of Evaporator Freeze-Ups.

Also, since its not OFF with switch in the OFF Position, the likely culprit is the Cycling Switch on the Accumulator. That controls on/off of the Clutch. They do go bad. But, rarely. Ours are old, so.... See if the clutch disengages when its disconnected.
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Old 08-26-2017, 02:20 PM
natedog37 natedog37 is offline
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OK, so this morning I disconnected the cycle switch while the truck was running and there was no change. The condenser was still running with the clutch engaged. This was with the AC switch in the off position. Should this have affected anything? Or should I just replace the switch on principal since its not cycling on and off?
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Old 08-26-2017, 06:03 PM
natedog37 natedog37 is offline
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WELP, It's not the cycling switch. Luckily it was only $15 bucks at Napa. I guess I'll start hunting down a short. Just so I can wrap my pea brain around whats happening correct me if I'm wrong: Possibility #1 The compressor needs a ground to turn off? and maybe this is interrupted so it's not turning off? But....#2 When I unplug it while the truck is running with the switch in the off position it WILL disengage, therefor not being grounded and turning off (not to mention no power to the magnet). So this would this mean that it needs a ground to run? this sounds more like it. Sorry, just thinking out loud. Either way I guess I'll start really inspection the wiring very closely. This is a new compressor with the clutch installed at the factory, so I'm assuming the gap is correct.
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Old 08-27-2017, 09:26 AM
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Quote:
Originally Posted by natedog37 View Post
WELP, It's not the cycling switch. Luckily it was only $15 bucks at Napa. I guess I'll start hunting down a short. Just so I can wrap my pea brain around whats happening correct me if I'm wrong: Possibility #1 The compressor needs a ground to turn off? and maybe this is interrupted so it's not turning off? But....#2 When I unplug it while the truck is running with the switch in the off position it WILL disengage, therefor not being grounded and turning off (not to mention no power to the magnet). So this would this mean that it needs a ground to run? this sounds more like it. Sorry, just thinking out loud. Either way I guess I'll start really inspection the wiring very closely. This is a new compressor with the clutch installed at the factory, so I'm assuming the gap is correct.
I looked at the diagrams and it's not a ground thing. It's a pretty simple circuit where power goes thru the dash switch, then thru a cycling switch then thru a containment switch then directly to one side of the AC compressor clutch. The other side of the of the clutch goes to ground.

Seems like you have power all the time which is impossible unless the dash switch it shorted, doubtful. When dash switch is OFF position there is no power to the clutch. Is it possible someone ran a different wire directly to power to the clutch bypassing the factory wiring? Only thing that makes any sense.

Depending on the year of your truck the power wire going to the clutch is Tan/LT GRN.
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Old 08-27-2017, 04:21 PM
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IS your truck an 02? The schematic for 02 shows a relay for the clutch on the a/c. Its says it the engine compartment in the same box with the trailer tow relays. The pic shows two mini relays and one regular bosch style. It is the bosch style. Unplug it and see if it stops. May be a fused relay. The pcm takes the inputs from the switches and provides ground to term 85 to energize the relay. term 86 is keyed and term 30 is hot at all times.
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Old 09-12-2017, 03:43 PM
Bronco308 Bronco308 is offline
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my '01's A/C was doing the exact same thing; Freon was low.
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