OEM Air Conditioning Troubleshooting

[1151]

With summer rolling around it’s time to get the A/C working. This is an 1152 ECV truck.

Is there a TM that outlines the full circuitry and troubleshooting steps?

So far I know the heater works, hi low fan works (albeit inversed, low is hi and hi is low).

The only feedback I get from A/C switch activation is the Thermopower solenoid near the coolant overflow tank. A/C on the solenoid is retracted. Heat on the solenoid is extended. Not sure if those are inverted too?

What I am not seeing or hearing is any feedback from the compressor kicking on or off. I observed the condenser and A/C gear under the passenger side rear fender near the fuel filler and have never seen the fans kick on or off or any feedback of any kind.

Any thoughts on where to begin or a full TM for A/C troubleshooting? I have no issue following wires with a multimeter but need to know where to look.

Thank you!

 

[veespo91]

I would check the ac charge should be 3.8oz for a four man 1.7oz for two man. If the system isn't charged the fans will not come on. I would start there.

 

[TOBASH]

On my m1165 and my m1151-1 alls I did was add R134a. Takes a huge amount.

On the M1165 the clutch didn’t move until I added half a 20 oz. can of r134.

Rear blows cold. Front blows hot. I guess I need to look into stuck heater valve.

 

[cwc]

Here's what I have on it...

 

[1151]

Thanks for the feedback and diagrams. Initial attempt to recharge was not successful - the low side charge is showing ~100 psi, well into the red on the recharge bottle. PSI does not change with engine on or off and the compressor is not engaging.

Not seeing any voltage on wires 7 or 436 heading into the compressor. Going to walk through the diagrams @cwc provided!

Any other thoughts? I appreciate all the help!

 

[Coug]

I would check the ac charge should be 3.8oz for a four man 1.7oz for two man. If the system isn't charged the fans will not come on. I would start there.

You sure those numbers are supposed to be ounces and not pounds?

 

[Mogman]

You should invest in a set of gauges, it is the only way to properly maintain the coolant level in an A/C system, they are very cheap at for example Harbor Freight and good enough to get the job done.
If you had 100psi in the system then the compressor and condenser fans should have tried to run, as you said time to work through the schematics to find the issues.
Having pressure is a good sign at least you do not have a major leak...

 

[veespo91]

On my m1165 and my m1151-1 alls I did was add R134a. Takes a huge amount.

On the M1165 the clutch didn’t move until I added half a 20 oz. can of r134.

Rear blows cold. Front blows hot. I guess I need to look into stuck heater valve.

The plastic valve is notorious for breaking off inside

 

[veespo91]

You sure those numbers are supposed to be ounces and not pounds?

3lbs. 8 oz 2lbs. 7oz I should have been more clear