M1151 front AC not working - $10 fix

[Autonomy_Lost]

I'm posting this in case it helps someone else. When I got my M1151 from gov planet it was listed as "AC compressor doesnt engage." To my surprise the compressor worked fine, but it only blew cold for the rear AC. The front AC blew at ambient temperature, gradually getting hotter as the vehicle warmed up.

This stumped me at first, because the front and rear AC systems share the same compressor. If it was an issue with the compressor or refrigerant level, surely it would affect both the front and rear, right?

Anyway I measured both the high side and low side refrigerant levels and they were slightly low. I added some r134a which brought the levels back up but the front still wasn't blowing cold, especially after the engine warmed up.

Through some researching and troubleshooting I discover there is a valve on the heater core that is supposed to stop coolant flow into the heater core when the AC is turned on. I confirmed that valve is receiving 24 volts when the AC is turned on, but it doesnt move. I suspect its stuck in the open position. So I'm effectively running both heat and AC at the same time, and the heat wins.

Turns out that valve assembly is something like 200 bucks. As a stop gap, I bought a 3/4 pex ball valve from Home Depot for about ten bucks, which fit perfectly in it's place. I installed it, put it in the off position and tried the AC. Blows ice cold front and rear now!

I'll eventually get the right replacement valve, but this was a cheap and quick fix that got my AC working. And if I ever need to run heat I can just pop the hood and open that valve.

 

[Backdraft]

I believe the thermotion actuator is a common problem for those. the valves are pretty solid. I figure a good choke cable will also do the trick.

 

[Autonomy_Lost]

I believe the thermotion actuator is a common problem for those. the valves are pretty solid. I figure a good choke cable will also do the trick.

Yeah, the actuator is definitely shot. The valve itself seems okay-ish, but it actually doesnt seal up all the way in the closed position. I completely removed it and moved it open and closed with my fingers. In the closed position I can still blow through it, so it will definitely let some coolant through. The ball valve will let none through whatsoever.

 

[M1165A1]

The older style valves from the M998s with pull cable are a much better choice and also a cheaper replacement. I've had two of the solenoid actuated versions go bad on me.

 

[Autonomy_Lost]

The older style valves from the M998s with pull cable are a much better choice and also a cheaper replacement. I've had two of the solenoid actuated versions go bad on me.

You know, that brings up an interesting point. With the new style, its either on or off, there is no in between. With the cable style, you can use it like a mixing valve. So by partially opening the valve you could allow a little heat into the system, giving you full control over the temperature of the AC like in a normal car. Hmmm...

Edit: I also noticed the old style is brass, compared to the new plastic ones. I could do a full retrofit including the valve, cable and overlay (I would just cut out the part of the overlay that says cold------hot or whatever) for about 50 bucks.

 

[Autonomy_Lost]

Well, I think I may have the only M1151 with manual temperature control now.

 

[Retiredwarhorses]

I install and have been installing the old manual valve on all my trucks, i use the AC only, could care less about the heater, if I need it, I can open the hood and move the lever. This option may not work for those in colder climates.

 

[Autonomy_Lost]

I install and have been installing the old manual valve on all my trucks, i use the AC only, could care less about the heater, if I need it, I can open the hood and move the lever. This option may not work for those in colder climates.

It was 37 degrees when I woke up this morning.