Ok a little back story first.

My ac has been freezing up inside the cab since I bought my 06 hummer a month ago. I have been dealing with it by just turning the ac off till it blows fine again then turning it back on. Sometimes I can drive all day and it won't freeze up and others it does it every 20 or so minutes. Also if i turn the know off full cold it blows hot. I need to do the 68 ohm 1/2 watt resistor to fix that just haven't gotten to the electronic store to buy some.

Now on to a problem that just happened. I was driving and the ac froze up so I turned it off about a minute before I parked the h3 for about 2 hrs. When I got back in to leave I turned the ac back on only to have it blink at me three times and turn back off.

I have tried to recalibrate it several times and it cycles thru all the settings but the ac still won't turn on.

I checked all the fuses and swapped around both the relay and the diode. I unplugged and replugged both the low side switch and the ac cluch connector. None of these steps worked.

I only have a low side gauge that hooks to an r134a can and it shows a static pressure of 100. This is with the compressor not running. I didn't want to try and jump the ac compressor until I got more input. Also I can turn the compressor by hand.

 

After having done more digging around and testing I found a short to ground on the a/c request wire. I did lots of ohm checking and the only time there is a short to ground is when it's plugged into the bcm. I have ohmed out the wire at all points leading to bcm and as long as I have the black plug unhooked I do not have a short to ground. If the plug is hooked up I have a short to ground with around 6000 ohms of resistance.

Is there anyway to rule out a bad bcm or any further testing. Based on the wireing diagram I have it appears that the bcm translates that to the pcm thru serial data lines.

Any help would be appreciated. Thanks

 

Sounds like your R134a has left the building (rig in this case). The only way to get a clear picture is to measure/monitor the high and low side pressures. Your low side pressure of 100psi seems high sort of like when the Freon leaks out. This would definitely disable the compressor. Remember, the A/C has an Evap. temp. sensor which triggers a low refrigerant signal to your HVAC control module. And there is also an A/C refrigerant pressure sensor on the high side hose to the compressor.


As for the "short", a measurement of 6k ohms is definitely not a short. You're more than likely measuring the impedance of the circuit.


I think a good 'ol manifold gauge set is your best bet at finding the culprit.

 

I only have a low side gauge and I hooked it up and jumped the compressor it blows ice cold and the pressure is right around 60 psi with it running. Do you think it could be my evap temp sensor. I ohmed it out and it seemed good but I don't know for sure cause I couldn't get back to the plug it's self without pulling the whole hvac module from under the dash.

 

60psi, is high for the low side.

 

Okay good, you jumped the a/c clutch and the compressor does its thing and it still blows cold. According to the 'compressor controls schematic' the 'A/C refrigerant Pressure Sensor Signal' is responsible for enabling the 'A/C Clutch Relay'. And according to the service manual if the pressure is TOO low or TOO high (above 428psi) then the ECM will not allow the A/C compressor clutch to engage.

So, what you need to determine is if the pressure IS actually low/high or if the sensor is bad. This will shed some light on your freezing issue as well.

 

After hooking up some gauges. The pressures were in rage of the chart you posted.

I went back thru the system and I was miss reading my short. It is a 68 ohm short to ground that goes away when unplugged from the bcm.

I can get a bcm from a local junkyard for 50 bucks do I need to program it or can I just plug it in and test it?

 

I just tried a junkyard bcm. It still only shows a short when the black plug is hooked into the bcm. I didn't have the bcm programmed so I couldn't start the hummer but the ac light still would only blink. I don't know what the next step would be. Other then taking it to a professional. Does anyone else have any ideas?

 

Ok after two and half hours of testing with a scan tool it was determined that it was my evaporator temperature sensor. They don't sell a replacement part that I can find so I looked up the specs and said a good ohm range for it would be from
~8900ohm to ~15000ohm
Which would be a evaporator temperature of
~86 to ~58 respectively
So I cut out the sensor and put a 10000ohm 1/2 watt resistor. In place of the sensor. It seems to be working great with no issues.

 

Thank you for following up on your efforts. Just be sure to replace the resistor with a sensor once you get one. Otherwise you could rupture a line if it freezes over too much. Good job none the less!