M915 air conditioner question similar to Humvee

[jamboly]

I just got one of the new Red Dot air conditioners (RD-2-4530-0) for my M920. Instructions with it were for an M915, for which I had to do a few mods to make it work, but I got it installed and charged up. The problem is the high side pressure was running to high, but cooling. I let out some of the R124a and was able to bring it down to around 175lbs, but then it doesn't cool. I charged it back up to about 225lbs and it cools a "little". I just now realized that the fans for the condenser unit are not coming on and coils were hot. Does anyone know where I can get a schematic diagram to help me troubleshoot this thing?
PS I could only find one circuit breaker, a 30a on the side of the evaporator unit inside the cab, and it was good.

 

[MWMULES]

I thought the red dots used 134a.

 

[M35A2-AZ]

The fans should come on when it gets to 280psi and turn off about 230psi.
How much 134a did you put in it? It should only need about 4lbs.
The low side will run about 30-45psi.

 

[74M35A2]

Typical high side for R134a is approximately 2 x ambient temp + 20%. Easiest if the fans are just on continuously when the A/C is on. Secondary way would be to trigger the fans on/off with the compressor clutch. Third way would be a high pressure switch trigger as mentioned above. All are easy to configure with a 24V relay.

 

[jamboly]

Thanks guys, the info you have given me will help me get started on troubleshooting without the schematics. Even though there are six wires on the condenser end of the wiring harness, there are only two wires in the connector that mates to it coming up along the back of the cab. I therefore assume that has to be a 24volts. I will start there to see where to look further.

 

[M35A2-AZ]

You do not use the two connectors on the condenser that look like they go to dryer. Use the ones on the other wiring harness.
If your system is not getting up to 280psi your fans will not turn on. If you short the wires out at the connectors (yellow and orange)the fans should come on. That is the wires that go to the fan pressure switch.
Here is a tread that has the TM for the M915 install. Post #25
http://www.steelsoldiers.com/showth...g-a-c-install-project/page3&highlight=ac+m915

 

[jamboly]

You do not use the two connectors on the condenser that look like they go to dryer. Use the ones on the other wiring harness.
If your system is not getting up to 280psi your fans will not turn on. If you short the wires out at the connectors (yellow and orange)the fans should come on. That is the wires that go to the fan pressure switch.
Here is a tread that has the TM for the M915 install. Post #25
http://www.steelsoldiers.com/showth...g-a-c-install-project/page3&highlight=ac+m915

The TB referenced in another post has pretty much everything you need to know about this AC system. After verifying that the fans worked when putting a jumper across the yellow and orange wires. I charged it up some more. It now blows cold air. Only difference is that my Condenser fans don't come on until I reach about 290-300 on the high side. Low side is 24-30, which is a little high based on referenced TB, but I am going to let it ride. Readings were at about 94deg f running at 1200 rpm.

 

[Artisan]

You do not use the two connectors on the condenser that look like they go to dryer. snip

You can clean that up significantly by just buying a 2 Pin Deutsch connector
and deleting the extra dryer connections. It's really easy.

You just disassemble things and remove the aux. dryer connections and put
it all back together w/ a 2 Pin Deutsch connector. No special tools needed.
I did an Expose' on this in my "Artisan's M916" thread HERE.

 

[M35A2-AZ]