AC Diagnosis: Help me prevent throwing parts at my M998

[FlameRed]

I have done lots of successful AC repairs in my time on a bunch of cars. But since I don't have much experience with my M998, I thought I would ask the collective's advice.

When I first got my M998 last year, the AC was a bit warm, and the sight glass showed bubbles. So I added about 3/4 of a can of R134 and good as new. All pressures in the expected range. I just assumed, it needed a top off. All good after that.

Now fast forward to about a year later and it is blowing hot. And something seems to be making occasional strange noises now also.

Sight glass showing bubble again. So low on Freon again. I assume I have a leak somewhere.

First thing I did was run my Freon detector and everything in the engine compartment was negative. In the pass compartment, the pipes going into the evaporator passed, but when I places the detector in the AC "cool" air stream out of the front vents the detector went crazy! So I assume I have a leak in the evaporator somewhere.

The system I have is the one that has four vents in the front, and two others on each side to blow on the pass and driver. It fits under the radio shelf. It has four black vents on the front in a line, on a tan colored housing and another vent on each side blowing on the driver and pass. I am not sure what they call it? All the inside parts fit under the radio shelf. Anyone know what this system is called and if I can obtain the evap for it or the entire evap unit?



Put the gauges on it and low side show 20 lbs, and high side shows 0 psi?!?!?! I thought that was impossible? I thought I did not have my guages hooked up right, but checked the professional, made in the USA , gauges multiple times and no pressure on the high side, 20 lbs on the low side? Not sure how that is possible. So do I need a new compressor? Replaced compressors on other cars so no big deal for me. I see this part number is reasonably priced at $180 brand new. No Humvee tax! But that is very weird.

I am almost tempted to take it to a local AC place to get a second opinion, but most of them around here have proven to be shysters. Besides, finding local local shops willing to work on HMMWV around here is very difficult.

 

[Autonomy_Lost]

It does seem like the leak is in the evaporator. With the unit being under the radio shelf, I'm thinking its aftermarket of some sort? Can you find a brand name on it anywhere?

 

[FlameRed]

It does seem like the leak is in the evaporator. With the unit being under the radio shelf, I'm thinking its aftermarket of some sort? Can you find a brand name on it anywhere?

I did not see any obvious vendor markings as I suspect they are under the radio shelf. I was thinking it may be impossible to find a direct replacement part.

Maybe someone can recommend one of the newer under dash units on the pass side where I could just buy a different interior setup, without paying thousands of $, and not the whole system?

EDIT: Yikes! Only $3500 for the newer generation interior part of the system?!?!?! HMMWV Tax it is finest. Maybe I can find someone local that can braze the leak in the existing evap...

EDIT: I found many Youtubes showing evap coil leaks can be repaired. Looks like I need to find a shop that has the skill to solder them. I eill report back...

 

[Dieselmeister]

I have done lots of successful AC repairs in my time on a bunch of cars. But since I don't have much experience with my M998, I thought I would ask the collective's advice.

When I first got my M998 last year, the AC was a bit warm, and the sight glass showed bubbles. So I added about 3/4 of a can of R134 and good as new. All pressures in the expected range. I just assumed, it needed a top off. All good after that.

Now fast forward to about a year later and it is blowing hot. And something seems to be making occasional strange noises now also.

Sight glass showing bubble again. So low on Freon again. I assume I have a leak somewhere.

First thing I did was run my Freon detector and everything in the engine compartment was negative. In the pass compartment, the pipes going into the evaporator passed, but when I places the detector in the AC "cool" air stream out of the front vents the detector went crazy! So I assume I have a leak in the evaporator somewhere.

The system I have is the one that has four vents in the front, and two others on each side to blow on the pass and driver. It fits under the radio shelf. It has four black vents on the front in a line, on a tan colored housing and another vent on each side blowing on the driver and pass. I am not sure what they call it? All the inside parts fit under the radio shelf. Anyone know what this system is called and if I can obtain the evap for it or the entire evap unit?

View attachment 893526

Are those refrigerant hoses attache with hose clamps? If so, check them for leaks. I doubt hose clamps can hold the high pressure side pressure.

 

[juanprado]

Red dot uses clamps and crimp on bands like cv joints with their own brand fittings so they can be field repaired without a hydraulic crimper.

 

[FlameRed]

Are those refrigerant hoses attache with hose clamps? If so, check them for leaks. I doubt hose clamps can hold the high pressure side pressure

I did check those connections and no leaks from them. I was surprised they would hold that pressure too!

I plan on taking it apart so I can look for hidden part numbers and the exact leak location

 

[FlameRed]

Red dot uses clamps and crimp on bands with their own brand fittings so they can be field repaired without a crimper.

Mine does look like one of the Red Dot headliner units I see in their catalog. Mine has a seperate controller. Once I remove the radio shelf hopefully I will see a model number and I can just order a new evap once I locate the leak precisely

Thanks for pointing me towards Red Dot.

 

[FlameRed]

Well, two steps forward, one step back.

I took the unit completely apart and I did find the leak. With the truck running, the detector goes crazy at the rear of the coils, near the fans, near the bottom. Nothing detected near those hose connectors.

The bad news is that the coil is a brick, and there is no way to get at it to braze it. I got to find a replace evap.

Also, more bad news, other that "QC-Passed" sticker, there is no model, no manufacturer name anywhere

 

[juanprado]

That does not look like the OE military or red dot system but aftermarket?

 

[FlameRed]

Yeah, I looked at just replacing it with a Red Dot, but the Red Dots are too wide to fit under the radio shelf. I am trying to avoid having to redo the whole system, or just keep filling it up with Freon every few months.

I found this one, made by Red Dot, that is supposed to be military for the M998. Does this install in the front and replace the existing radio shelf? Looks like it has connectors for some controller I don't have.

 

[Dieselmeister]

Look at this as a generic replacement.

Amazon.com: Universal Under Dash AC Evaporator Underdash A/C Air Conditioner Heater Unit Heat & Cool 404-000 4 port 12V HVAC Unit : Automotive

 

[FlameRed]

Thanks for all the guidance. After measuring the space available under the radio shelf, trying to not have to reposition the AC hoses, and looking for a 24V universal underdash unit which the old one seemed to be, I ordered one that should fit. But I have to find some new vent "registers" or whatever they are called as the new one did not come with any vents.

Hopefully I will not get stuck trying to figure out the wiring!

I'll report back...