This is a cross-post from another forum/site.

I moved to Chicago last year from Arizona, from super hot summers to really cold winters.

Last year I added the Max AC Assist from Diesel Site. It worked great, and the cab was very cold. Now that I've been through a cold winter, the weather is warming up, and I went to start using the AC, but it just blows hot.

This is what I've done to troubleshoot:

Pretty sure I have two problems: a vacuum leak and an AC issue.

Vacuum leak:

I can confirm in all settings but one on the air direction control, the pump reaches the right pressure and turns off. But with the switch set to Max, the pump runs forever.

1) I watched this video and can confirm the pump and reservoir are working fine.


2) Hooked up a hand pump to the vacuum tube that runs into the truck. With AC switch in any position other than MAX, hand pump was able to pull and maintain a 20, which coincides with my first finding.
3) With AC switch in Max position, pumped as fast as I could, but could not maintain pressure. Seems like there is a leak somewhere.
4) Isolated and tested vacuum line to Max AC Assist device using hand pump. Was able to maintain a 20 and confirmed the device moved and stayed in the correct position as designed. Ruled out Max AC Assist and associated tube. No leak there.
5) Disconnected tube that connects to silver ball under blend door. Hooked up hand pump directly to this silver ball. Door is closed by default. Pumped as fast as I could, and could get the door to slightly open and then close, but could not get door to remain in open position. Leak in silver device, or bad blend door?
6) with everything plugged back in, the AC control will correctly direct air to the defrost vents, to the defrost & floor, turn off and go through the forward vents. But there is no difference between forward, AC, and max in terms of air temp or speed. I would expect the AC to turn on (if it was working), and with it on Max, run faster/recirculate. It seems to run the same speed.

Help!

The second part of the problem is even if the air is blowing through the defrost vents, floor vents, forward vents, or with the setting in the AC or max position, the air is warm and not cold. I'm guessing I have a small leak that worsened in the winter, and have lost my refrigerant.

Next steps?

 

By any chance does this occur with 4wd engaged, or is it a constant issue?

 

For the first problem, check the vacuum circuit from the control head to the recirculate vacuum motor which is located behind the glove box. Since your accessory device had to tee into this vacuum line, it is now part of this same circuit and it also must be checked. Look for a broken or loose hose or fitting or for one of the vacuum-controlled devices to be leaking. I have no idea what a "silver ball" might be.

As for the second issue (no AC), go look under the hood and see if the compressor clutch is engaged. Basic observation.

Leaks in the 4WD system cannot cause problems with only one subsection of the climate control system.

 

Thanks, I will check. I presume I have to pull the entire dash, right? If so, any pointers would be appreciated.

 

My pointer would be to avoid pulling the dash.