| Re: Let's troubleshoot my a/c system...aka Need help verifying voltage at ac compressor |
Subject: Re: Let's troubleshoot my a/c system...aka Need help verifying voltage at ac compressor by Matatk on 2012/7/17 1:21:57 Quick update on this. I stopped at the u-pull yard today and actually found a bcm in an old Cadillac. Amazing. Only cost about $18 out the door. I was happy. Came home, put it in, still wouldn't fire the a/c clutch. Darn it. So I tested the system anyway since I have the gauges there. When manually engaging the compressor (fan switch disconnected so it runs) I was getting pressures on the low side in the 20s and on the high side around 225. I'm happy with that. So that tells me that system is charged correctly and there are no obstructions internally. Got a chance this evening to do some real troubleshooting, what I should have done in the first place. It's a pia, though, since you have to pull the dash panels apart. Coincidentally, since my car is in a constant state of repair, I just leave all the screws out of the console and dash, etc so it takes all of 30 seconds to get to the heater control head. I swapped that out with a spare I have just to double check, that was not the issue. So here is goes: Isolation test 1: Pressure cycling switch should ohm less than .5 ohms, passed. (says to check refrigerant charge, as well, which I already know is good from above) Isolation test 2: BCM disconnected / ign switch run / a/c auto 65* / outside above 60* -A (dk grn) connector C1 to ground should be battery / pass -C (dk gn/yel) C2 to grd greater than 10 v / pass Isolation test 3: Fused jumper at BCM C1 / ign run -A (dk gn) to ground - clutch engages / pass Test A: Heater controls (I tried these tests with both head units and both blower control modules with almost identical results) Testing wires at a/c head unit behind dash ign run / ac auto 65* / outside above 60* -C1 (lt grn) and ground s/b less than .5 volts - actual .05 v / pass -C6 (dk blu/whi) and ground s/b greater than 6 v - actual 5.88-5.92 v (FAIL?) -C3 (dk grn/or) and ground s/b 4-6 v - actual 6.06/6.3/6.98/7.24 depending on head unit/bcm combo (FAIL) -change a/c mode to econ C3 (dk gn/or) and ground s/b less than 1v - actual .06 v / pass It appears it did not pass two parts. Diagnosis: 1) Check the lt grn 66 wire and the black 904 wire for an open. If wires are good, check the a/c high pressure cutout switch and pressure cycling switch are closed. If the a/c high pressure cutout switch is open, replace it. If the pressure cycling switch is open, refer to section 1b for normal refrigerant level. If refrigerant level is normal, replace cycling switch. Since I passed the first part, I am assuming the switches are good. But I have no way of testing the high pressure cutout switch that I know of. Pressure cycling switch passed the ohm test in isolation test 1. Any ideas on testing the high pressure cutout switch? I know I can jumper it when trying to run the system, but I mean an actual systematic ohm or voltage/load test. 2) Check for a short to ground in the dk blu/wht 997 wire. If the wire is good, refer to section 6E (wiring harnesses, etc). I was close on this one. I think the bcm could be causing it to be slightly off. Perhaps some corrosion? I don't think there is a ground/short issue. 3) Remove bcm connector C2. Repeat the measurement at C3 (dk grn). If the voltage does not chance, check the dk grn 959 wire for a short to ground. If ok, replace the heater and a/c control assembly. If the voltage increases to 10 v or greater, replace the bcm. I did this test and the voltage rose to around 12.22-12.27 for both bcm/head units. So I obviously have TWO bad blower control modules. My original and the junk yard replacement. 4) Replace the heater and a/c control assembly. I passed this test, so this does not apply. Sooooooo... I'm gonna look for another blower control module tomorrow at another yard. If no luck, I'll buy a new one for $100. I'll keep updates going as I get the parts and testing done. |
