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1987 Corvette, working to diagnose an HVAC issue. Blower is not functioning, I have the control unit set to ECON but have tried all other modes and have also tried the blower at all speeds (1 through 10). I can hear the clicking of the HVAC head unit, I know it is controlling some solenoids for the blend doors etc.
I have tested all fuses that are on the right of the dash, all are good. I have also tested the 10amp fuse under the dash above the blower motor, it also tests good. I also cleaned up the ground near the blower motor, but that has not made a difference. It was not in bad shape to start with.
The power connector going to the blower motor I test 1.46v. That is with the Key on, blower @ 10 in ECON mode.
I am asking where I should go from here? It does not seem I am getting proper voltage to my blower motor.
Blower motor does function just fine with voltage applied to it directly.
Hi, you may have found this already but here's a copy of the HVAC electrical diagrams and troubleshooting. The C68 option HVAC starts on page 15 of the PDF. It is from '86 but should be the same as 87. Is the 1.46V the blk/red wire coming from the blower control module (thing with two plugs on the top of your blower motor housing, if you remove it it looks like a large metal heat sink) to the blower motor?
Yes, I can measure 1.46 volts at the blk/red connector either at the blower control module or the blower itself. Thanks for the PDF, I printed it off and am going to work through the troubleshooting procedures. I am suspecting the blower control module but I am trying to rule out anything else.
Yes, I can measure 1.46 volts at the blk/red connector either at the blower control module or the blower itself. Thanks for the PDF, I printed it off and am going to work through the troubleshooting procedures. I am suspecting the blower control module but I am trying to rule out anything else.
Likely is the control module, which can be hard to find a replacement for though I think a Cadillac model had an exact replacement. Often they fail in a state that leaves the blower motor constantly running even with the key off. It may be worth measuring the voltage of the brown wire going into the control module.
I have a replacement on the way, a few different people are making it but I went with the ACDelco part as that is what was there originally. I supposed the only other thing it could be is the control head, I really hope its not that.
One thing I notice, you say test the brown wire. I have a green/yellow, a black (or looks like black) a black/red, one smaller wire that looks a little bit purple. Not sure if this is due to the difference in years or I have a wiring issue. I am looking at the schematics in the PDF and the A,B,C,D on the C2 connector and things just don't match up in terms of color.
I attached some pictures of what I am talking about.
Great news, I swapped in a new Blower Control Module I got from the GM dealer and the blower is working again at all speeds, blend door seems to operate just fine.
Looks like I will be moving onto charge the A/C system next. Does not look this this car was ever converted over to 134a so I will have to run out and get those quick connects and evacuate the system to pull a vacuum to make sure there are no leaks.
I did quickly test the low pressure and high pressure switches, high pressure is closed as it should be, low pressure is open which would indicate less than 25psi on the low side(or a bad switch). Once I have the conversion fittings I will be able to determine exactly how low.
Thanks for your help so far.
Lawrence
Last edited by Lawrence Kennette; Jul 27, 2018 at 09:16 AM.
That is great news! When I converted my '87 to 134a I seem to vaguely remember also changing over an orifice tube and filter. I forget if it was out of "while I'm doing this anyway" or if they were 134a specific.
So far the only thing that might be different is the low side pressure switch due to the lower pressures for R134, however there seems to be an adjustment on the back of the pressure switch.
This morning I did start the car up and jumper the low side pressure switch to make sure the clutch engaged and it did, I only let it run for like 3 seconds to make sure the clutch was ok. There is pressure in the system but just not enough (and I don't have any R12). I think if the system was open for any length of time it would be good practice to replace the orifice tube and accumulator.
Quick question the ECON button (economy?) what does that do on the control unit? A/C operated in auto mode.
More great news, system held a full vacuum overnight so I did a full charge of R134 and it blows cold! Far colder than I expected from a 31 year old car.
Also added a little dye so if there are any future leaks I need to chase it will be easier.
1987 Corvette - HVAC Blower
