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AC electrical issues

JedVT

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hey guys, I’ve got a 2001 WH statesman l67

Okay so I’ve had my air con regassed professionally and pressure tested, there’s definitely no leaks and we’ve replaced the o rings with genuine ones, pressure checked it again 24 hours and still holds pressure


But the air con clutch will not engage


The high pressure switch is showing 5 v on two terminals but nothing on the other


The AC relay has power at the main power input and the relay coil input


The relay plug is not broken as we’ve tested it and even replaced it


We bridged the relay and that forced the clutch to engage


But we cannot get the clutch to engage any other way, even with a brand new relay

I’m extremely spun out, I’ve had auto eleccys look at it and they can’t understand what’s wrong, if it helps at all, sometimes I have electrical issues like my rear windows sometimes work, sometimes don’t, my number plate light occasionally turns off, several dash lights are out, once one of my tail lights randomly cut out

Thanks
 

ltdslip

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A/C relay gets a ground ( AC enable) via the Power Train Control Module
 
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JedVT

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A/C relay gets a ground ( AC enable) via the Power Train Control Module
Okay, how would I go about checking this earth? I’ve got a multimeter and all the tools to access the pcm
 

ltdslip

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switched electronically in PCM
hope attached diagram works..
 

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ltdslip

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if it helps at all, sometimes I have electrical issues like my rear windows sometimes work, sometimes don’t, my number plate light occasionally turns off, several dash lights are out, once one of my tail lights randomly cut out
Might sound weird, electrically unplug the ABS module & try it.
 

ltdslip

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The high pressure switch is showing 5 v on two terminals but nothing on the other
From the manual... "The A/C Refrigerant Pressure Sensor is a sealed gauge reference capacitive pressure sensor with
on board signal conditioning. It provides a 0 to five volt output and requires a five volt regulated power supply."
 

ltdslip

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if it helps at all, sometimes I have electrical issues like my rear windows sometimes work, sometimes don’t, my number plate light occasionally turns off, several dash lights are out, once one of my tail lights randomly cut out
What will doing this eliminate?
Do a search for ABS module,
Suspect ABS module sometimes causes weird faults to popup, I think the cars modules interconnect on a serial data bus.
 

Skylarking

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With weird electrical issues where computers are involved, diagnostics 101 dictate you disconnect the battery and after a few minutes reconnect it to force a cold reboot :p always worth a try ;)

If the AC Refrigerant Pressure Sensor is OK, though i can't find it in the wiring diagram @ltdslip provided, you need to trace out and test the wires between the sensor and all connected devices to find where and how it's connected (be careful if the components are not dumb 12v devices as you can blow the electronics).

In your tracing and testing, if you can't find a wiring fault, and the sensor is OK, then it must be the module it's connected to at fault. Either the module has some electonic driver fault or it's programing is suspect and it doesn't know it needs to be turing on (earthing) the aircon compressor (relay wire).

It's difficult to fault find if how and where the pressure sensor connects is unknown while the logic on how the compressor is turned is also unknown. You need a better vehicle technician to check things as it seems beyong the auto elecs knowledge.
 

ltdslip

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A/C Pressure transducer connected to PCM

Master Reset also fixed plently of issues on 747's

Scan for fault codes?
 

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