Ac compressor not being called on
09-19-2011, 06:25 PM
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Ac compressor not being called on
Where do I start with this issue? Do I need to pull part the whole dash right away or is there anything to check first. It has freon I put gauges on but the compressor is not being called.
09-19-2011, 06:37 PM
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High and low pressure switches, amplifier, blown AC fuse (all behind glove box), among other things, can cause the compressor to not come on. I even had the wire to the compressor short out under the hood at one point. Check out the FSM for your truck (link in my sig) and trouble shoot away. 
Last edited by BMcEL; 09-19-2011 at 06:38 PM.
09-19-2011, 06:43 PM
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Fuse is good checked some of the wiring but ran out of daylight gonna try to diagnose some more tomorrow. Just wandering if there was anything particular that is a frequent problem
09-19-2011, 06:57 PM
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Low pressure switch and idle RPM cutoff adjustment on the amplifier ring a bell...that's where I'd start anyway. If the fuse is good, turn the knob on the amplifier while idling and see if the compressor kicks on, if not it's likely the low pressure switch. You can bypass it for trouble shooting purposes by doing this.
Is your AC light coming on when the switch is depressed?
Is your AC light coming on when the switch is depressed?
09-20-2011, 07:48 AM
#6
if its an 85 to 89....
is the blue light lighting up when you press the engage button? on my truck if the blue light does not light up its a problem with the switch in ac control....
otherwise..............
energize the compressor directly to the battery for a few mins see it if blows appropriately cold air, if its wimpy or not cold at all, you have no gas in the system and the low pressure limit switch is working properly, this will tell you if the system is healthy in general. if it is and you have plenty of gas.....
next trace the electrical path, via the manuals schematic, look for a relay with a burned contacts first, usually the clutch engage relay first because its switching a ton of transient current and takes a big arc the when the coil is switched on and off in rapid succession (oscillation followed by back emf from the coil in the form of a high current high voltage spike aka surge) by say a bad dash switch, or loose connection sometimes which often leaves tungsten oxide pits on contacts, a condition that tends to half cook the ECM I/O transistor gates on more modern trucks leading to general weirdness..........
otherwise..............
energize the compressor directly to the battery for a few mins see it if blows appropriately cold air, if its wimpy or not cold at all, you have no gas in the system and the low pressure limit switch is working properly, this will tell you if the system is healthy in general. if it is and you have plenty of gas.....
next trace the electrical path, via the manuals schematic, look for a relay with a burned contacts first, usually the clutch engage relay first because its switching a ton of transient current and takes a big arc the when the coil is switched on and off in rapid succession (oscillation followed by back emf from the coil in the form of a high current high voltage spike aka surge) by say a bad dash switch, or loose connection sometimes which often leaves tungsten oxide pits on contacts, a condition that tends to half cook the ECM I/O transistor gates on more modern trucks leading to general weirdness..........
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