M1151 M1165 M1152 A/C Charge

[Ted Gates]

Check ALL electrical connections.
Check ALL switch(s) wiring.
Verify ac charge.
Check/replace low pressure switch.
You might be able to supply 24vdc to ac compressors, . Make sure + to + and see if clutch engages.

Just ideas, your results may vary. Proceed at your own risk.

[Hell On Wheels]

FWI, the electric valve takes a minute or so to close, so you will get hot or warm air to start with, until it closes all the way. Just have someone watch it while you turn the a/c on, to verify if it is working or not, Or, take a pic of it before starting and then after a/c has been on for a couple minutes to compare. The valve is over by the radiator overflow tank. It has a 90 degree hose on each side. (5/8").
I don't put fan on HI until it starts blowing cold.
You can check the charge easily, too. Just like any other car. The hi and low ports are just behind the compressor.

Jason

I didn’t like the way this electric valve switch operated, meaning it functions to close the hot flow while the A/C is on. So, if it loses connectivity, you get hot water when the system is on. I bought the opposite switch (polarities) where it only operates to provide hot water flow when you want hot air. I bought it from the same company who makes them. This was one of the points they mentioned why the government designed specifications to operate the opposite. Again, I don’t have my A/C configured to milspecs I have a bootleg wiring. I’m sure Ted & Greg can explain in much more detail as to why the switch is wired in that specifications to keep the system from freezing or something way above my knowledge.

[Retired War Horses]

FWI, the electric valve takes a minute or so to close, so you will get hot or warm air to start with, until it closes all the way. Just have someone watch it while you turn the a/c on, to verify if it is working or not, Or, take a pic of it before starting and then after a/c has been on for a couple minutes to compare. The valve is over by the radiator overflow tank. It has a 90 degree hose on each side. (5/8").
I don't put fan on HI until it starts blowing cold.
You can check the charge easily, too. Just like any other car. The hi and low ports are just behind the compressor.

Jason

I didn’t like the way this electric valve switch operated, meaning it functions to close the hot flow while the A/C is on. So, if it loses connectivity, you get hot water when the system is on. I bought the opposite switch (polarities) where it only operates to provide hot water flow when you want hot air. I bought it from the same company who makes them. This was one of the points they mentioned why the government designed specifications to operate the opposite. Again, I don’t have my A/C configured to milspecs I have a bootleg wiring. I’m sure Ted & Greg can explain in much more detail as to why the switch is wired in that specifications to keep the system from freezing or something way above my knowledge.

The valve defaults to open when no voltage is present, when switched to AC, it energizes the solenoid and closes the valve…terribly I may add, so bad that I remove the valve and install the old version in its place.
Even brand new the OEM electric valve does not prevent coolant from flowing to the heater core, this causes hot and cold air to mix…my solution yields Nice ice cold AC.

[Retired War Horses]

Hey, I'm digging into the HVAC on my 1151 and 258xxx. So far, I jumpered the thermostat on passenger side, got the rear fan blowing. Compressor clutch will not engage. Replaced the heater core valve with a regular manual valve, dash still blows hot.

I jumpered the low side switch, compressor still wouldn't activate. I have 24v at harness.

With truck running, checking low side pressure the gauge shows 130psi with the trigger open, no pressure with trigger depressed (trying to fill).

I can hand rotate the clutch. Even if pressure was low, it should engage when jumping low side switch right? The engine bogs down just a little bit with low side switch jumpered, but clutch won't engage.

Can I jumper the compressor by running a ground wire and a 24v wire to try and get the clutch to engage?

Any help would be appreciated.

Take it to a professional, your system needs to be evacuated and recharged at minimum, the system takes 3.5lbs, you will never get a can from auto store to service this system, it needs a minimum of 1 pound before the compressor will stop short cycling.
You need gauges to see the the high and low side pressures based on OAT.