A/C Diagnostic help

[Pstyckiewicz]

I have an M1152A1 with the stock2 man A/C unit. I am just getting into the stage of fixing the A/C. The fan switch works on the dash. The vents blow air but it’s not blowing cold. I don’t hear the fans under the right rear wheel well turn on. I did hear them come on once before for a second. I’m not sure if I have a leak somewhere or if I have a bad low or high pressure sensor. Maybe a bad ground or wire issue.
I’m looking for somewhere to start. Maybe what wires to look at or connections to jiggle. Or O-rings to replace. I do have access to a vacuum to hook up to the system but I want to check the simple things first.

Any help is greatly appreciated!

 

[FlameRed]

First, let me state that I am a novice on the HMMWV, but there are certain things you can do.

Start by unplugging the connector at on top of the dryer - the low pressure switch. With the AC turned on, engine running, you should see 24V on one of the leads in the connectors with a VOM. If you don't have that - then you have electrical issues further down the chain. If you do have 24V, you can short the two lead swith a piece of wire for a couple of seconds and you should see the AC clutch engage and the compressor turn. If it does turn, that means you are low on charge - or empty of Freon. If it does not turn then you can look at something wrong with the clutch or compressor. If it does turn, then put a set of AC gauges on the high and low side and check your readings with the leads shorted again but I would bet your Freon level is low.

If the freon level is low, I usually whip out the freon sniffer and find the leak. If the thing is really low I might have to add a can of freon just to get something in the system to sniff out the leak.

Some auto part stores will loan out a sniffer and compressor gauge set for free with a deposit.

Hope this gets you started.

 

[Pstyckiewicz]

Awesome information!!! Thank you for taking the time to help me out!

 

[Pstyckiewicz]

The attached picture I believe is the air dryer wiring. There appears to be three wires from the relay. I’ll test it to see if I get 24v.

 

[Mogman]

Invest in a cheap set of gauges!! HF has them.

 

[Pstyckiewicz]

Got around to testing some stuff. So my volt meter wasn’t work. I just jumped the wires on the dryer and the fans turned on under the wheel well. I did not see the clutch engaging on the a/c compressor. Also the fan under the wheel well was running while in heat mode and when fan on dash was off. It seems to run all the time. Not sure if that’s normal. Any suggestions for what to look at next? Get some gauges from harbor freight?

 

[Pstyckiewicz]

So I put some gauges on the unit today while it was off. And got some pressure in there. I didn’t bother trying it while on due to the clutch not engaging. Attached is a picture of what I got. In addition I can turn the clutch by hand.

Any ideas on what to try next?
How to jump it to get clutch to engage?
Maybe it’s low on charge and put more in to get it to work?
Is there a way to see if compressor/clutchis bad?
Wires to look at? Already started following some.

 

[Pstyckiewicz]

Attached

 

[Pstyckiewicz]

.

 

[Pstyckiewicz]

Smaller connection/blue side is high pressure and bigger connection/red side is low pressure side. And again these are readings when the truck is off.

 

[mrfarb]

I’m using a set of gauges now - you have them mixed up, red is high pressure side, blue is low pressure side.

 

[Pstyckiewicz]

Haha figured I had it backwards. Any chance you have a similar reading on the gauges when off? I think I might go and put some R134A in and see what happens.

 

[Mogman]

The gauges should read the same when "off" as the system will equalize.

 

[Pstyckiewicz]

Do you think those measurements are low causing it to not engage the compressor or do I have a compressor problem.

 

[Mogman]

Do you think those measurements are low causing it to not engage the compressor or do I have a compressor problem.

Jump the low pressure switch and find out.

 

[mrfarb]

My low side is about 30, high side is about 200 but I’m at least 16oz low on Freon.

 

[Mogman]

My low side is about 30, high side is about 200 but I’m at least 16oz low on Freon.

The OP does not have a running compressor at this time so the pressures would be equal, of course it will not look that way because the gauges have different scales.

 

[Pstyckiewicz]

So I attempted to put some r134a in but it did nothing. Nothing kicked on. Tried jumping the wires between both low and high pressure switches nothing. Followed wires to see where they went and connections. So I found a wired connector that’s capped off. Looks correct?
Picture attached.
what I did do is ran a wire from the battery box +24v to the high pressure switch and the compressor turned on. I checked the wires on high and low pressure switches and it appears there is no power getting there. Not sure if there is suppose to be power? I’m think maybe an electric problem somewhere?

 

[Pstyckiewicz]

Also noticed the heater core attached to blower/ac unit was hot. Was running it on AC high fan?

 

[Mogman]

Do you have the schematic?
Start at wire 435 at the temp switch mounted to the evap, if you have power there continue with 438, 436 etc. if not back up towards the AC switch.