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Discussion Starter · #1 ·
A/C not working.
When I run 12 volts straight to the clutch it moves in and out as it should. Clutch Functions.
I placed a jumper in the ambient switch (low pressure switch). Still no voltage at the clutch.

In looking at the heater - AC control, the master switch is open when off or far left. Any other position, the switch has continuity. I am assuming this is not the signal to the clutch.

When the vent switch is on Norm the switch is closed and when on vent it is open.

The third switch is the fan speed control.

The question I have is where does the signal come from that goes to the clutch?
 

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Do the blower speeds work? If yes, then the problem lies between the blower speed switch and the compressor.

Schematic is for a 68 but yours should be similar.

Rectangle Schematic Font Material property Parallel
 

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Discussion Starter · #3 · (Edited)
Do the blower speeds work? If yes, then the problem lies between the blower speed switch and the compressor.

Schematic is for a 68 but yours should be similar.

View attachment 146496
I replaced the blower motor and wheel. The blower motor works except on high speed. This I believe is the relay (which is new but...). The compressor does not come on when on lower speeds.

So looking at the diagram, I can identify the Master Switch on the heater control (binary switch). I can also find the blower switch (Multiple Pronged switch). There is one more switch that controls the vent. My issue is finding the "Clutch Switch". This is obviously not a switch that is change directly by the driver. He selects AC on the master and a blower speed. What changes the clutch switch?
 

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I found the 69 A/C schematic in the assembly manual. Slightly different with the wiring colors.

The clutch switch (what you are calling the vent switch) is mounted on the control head.

The Ambient switch is not a pressure switch. It measures the outside ambient temperature. If below 50* (+ - 5*) it will open, not allowing the clutch to engage. It is mounted on top of the air plenum just above the blower motor.

Schematic Font Handwriting Material property Parallel



World Map Organism Font Schematic
 

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Discussion Starter · #5 ·
I found the 69 A/C schematic in the assembly manual. Slightly different with the wiring colors.

The clutch switch (what you are calling the vent switch) is mounted on the control head.

The Ambient switch is not a pressure switch. It measures the outside ambient temperature. If below 50* (+ - 5*) it will open, not allowing the clutch to engage. It is mounted on top of the air plenum just above the blower motor.

View attachment 146508


View attachment 146509
Thank you so much for the help. It is much clearer now.
 

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Touched up the schematic. Filled in faded lines to the blower motor


Font Schematic Parallel Handwriting Rectangle
 

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Discussion Starter · #7 ·
Thanks again. I am certain it is the ambient switch. Not able to find one online except at EBAY for $135. I appreciate the efforts you made here.
 

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You can use other GM ambient switches. Some are a bit larger but do the same thing.
 
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