Another AC problem

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Spareparts

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AC was not working when i got the truck. broken line, probably a bad pump. so,
I replaced all the under hood AC stuff. New lines, Pump, Condenser, Orifice tube, Dryer. Flushed rear lines until nothing came out after flushing with compressed air.
Pulled vacuum to about 30. let sit for 24 hours and all good. Charged it with proper amount of oil and R134A, 3Lb 8oz
AC blows cold when the system is on both front and rear.
AC Clutch will not engage unless i jump it at the pump with 12v or jump it at the relay. Fuse is good.
It will not turn on if i jump across both pins on the low pressure switch on the dryer.
If i jump the high pressure switch? at the compressor it does not come on but the AC fan on the condenser comes on.
When i check both pressure switches with a trouble light none have power. I think the low pressure should have power??
When i turn the AC switch on at the dash to max the recirc light and ac light both come on and the blend door for the heater blower moves.
Where does the power come from for the low pressure switch on the dryer?
Could it be a bad ac switch at the dash even though it does light up?
 

0xDEADBEEF

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I want to say the wire for the signal to the PCM goes from the connector at the firewall through the high and low switch to the PCM. That's what I recall from when we did the harness on my son's truck, but that was a year ago now. I am positive it goes through at least one of them.
 

HotrodZ06

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Maybe these can help.
 

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Spareparts

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Maybe another clue.
About 3 or 4 months ago after i put a aftermarket radio in it the interior lights stopped coming on when the door is opened. I checked and the fuse and it is good but have not dug into it any further.
Wonder if this is a ground issue?
Everything else seems to work fine but the headlight override switch will not turn the dome lights on either.
 

Spareparts

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I did find this also but have not tried it yet.

"well here's the theory first

your PCM (powertrain control module) decides when and IF it wants the A/C compressor to run

when the PCM wants the compressor to operate it supplies a GROUND for the A/C relay

Therefore... FIRST let's see if the PCM is commanding the relay

the easiest way to remove the a/c relay
install a small wire to pin 85 of the relay...it SHOULD be marked on the relay
re-install the relay

they make cool little adapters for this but they cost about $100 off the tool truck

then using a regular test light, install one end to the vehicle battery and the other to that little ground wire

turn your a/c on, engine running obviously, and see if your test light illuminates

if it does not, then we have to repeat this same test but this time at the PCM pin # 1 connector #3

again, if no illumination then we need to find out why the PCM is not commanding the clutch operation

if however, it does not illuminate at the relay BUT lights at the PCM then you have an open in the circuit between the PCM and the a/c relay"
 

Spareparts

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Tried the test above and at both spots the test light comes on dim and the ac pump turns on.
It will turn on whether the switch is pushed or not and running or not. Does not seem right?
 

Spareparts

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Welp, I give up, Electrical if NOT my strong suit by far and this proves it.
I can not figure out why the switch will not turn it on. I have replaced the CC switch panel. Swapped out the Relays under hood under dash.
Test light shows no power at the low pressure switch
Last thing i think i can try is a new (used)ECU
If i jump it at the Relay under the hood fuse box it works, Not as it should but it works and blows icy cold at 80deg outside.
Also replaced the Headlight switch and both front door switches and still no dome light when i open the door or move the dial all the way to the top.
They will come on if i press the switch on the dome lights themselves.
And yes all Fuses are good.
 
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