I have a 1993 Vette and am having some heat/AC blower problems. The problem is: fan doesn't turn on at all. If I set it to heat or cool and set the fan to any speed (1 through 10), nothing happens.

I tried a new blower motor, but that didn't make any difference--the motor never kicked on. I also tried a new blower relay--that didn't help either. I also tried all combinations of new and old (motor and relay), and nothing worked.

I checked voltage on some of the wires running into the relay, and they are reading 12V. I checked the wires running into the blower motor and they seemed low (<1V)--not non-existent, but low--even when the fan was set to high.

With the car off (but in accessory mode), I turned on the heat and heard a quiet click in the engine compartment, so I think the controller is sending some signal to the engine compartment. However, the fan still did not spin up at all.

Any suggestions at what to try next?

 

First thought that comes to my mind is the A/C programmer. I'm guessing that it's a control related issue, since you've replaced items already. Do a search for A/C programmers, or hopefully SunCr is around to offer his expertise. He indirectly helped my diagnosed much of my '86's A/C problems.

 

There isn't a Relay with Electronic Air. Low voltage signals are amplified by a Module - mounted on the Evaporator case - and that controls Blower Speed. Make sure that module has battery power - red wire. If not, check the Blower Fuse. If so, put the controls on "1" and check the signal wire - Brown - for 2 volts. If there, check the output to the Blower - Purple - for 4 volts. Raise Blower Speed to "10" and check the Brown wire for 6 volts; Purple for 12 volts. In the Brown wire has the correct voltages but the Purple wire is incorrect, replace the Blower Module. GM uses it across the line, so it's available from Chevy, Pontiac, Buick & Caddy. If the input voltages are wrong, you'll need to ohm out the Brown wire back to the Programmer. If it's ok, replace the Programmer.

 

Thanks for the info. (The relay I tried to replace was the AC compressor relay--my bad.)

I checked the voltates as you suggested on the module. I tested the single red wire, and that has 12V. I set the fan to 1 and tested the brown wire and it read 7.5V. I then set the fan to 10 and tested the brown wire and it still read 7.5V. So, something is definitely awry.

Anything else I should check before plunking down the $300 for the new AC Programmer?

 

An input of 7.5 volts should give an output of 12 to the blower so I'm thinking that the blower module is bad. These things are somewhat of a crapshoot because the signal from the dash on your Year is over a data line and you need a scanner (Tech 1 or 2 with bi-directional communication capabilities) to troubleshoot it. The Bulletin revising the diagnostics starts off using the Scanner to command the blower motor. If it fails, it then has you check continuity from the Control Head, Term 4, to the Programmer, Term 13 (which is probably the data line), and if it's ok, you replace the Control Head or Dash Assembly. If the Tech 1 can command the blower fan "on", you go through the diagnostics you've allready completed and if you get a voltage signal at high blower speed to the module (Tan line) - but no blower - you replace the Module. Without the scanner, there's a slight risk of replacing a perfectly good parts. I suggest that you check the ground on the blower module (Black) as well as the 5 amp fuse (should be labled A/C MDL 1 or something like that) protecting the return voltage signal circuit back to the Programmer. I can't be sure about this, but I think the Module might be the culprit (you did jumper the blower motor to the battery to make sure it works?)

 

Yes, I hooked the blower motor directly to the battery and it worked fine. Also, I checked all the fuses and they all were fine.

I don't have a scanner, so I can't really try that option. (Plus, they are big $$$ to buy aren't they?)

You mention to check the ground on the module. What specifically should I look for on that?

I may just take a chance and buy a module and see if that fixes the problem. For <$100, it's worth a shot.

Any tricks on removing it?

 

The module is held on by two sheet metal screws and the harness is keyed so that it only fits one way. A generic scanner is $150 or less, but won't provide the two way communication you need to troubleshoot the dash controls. Ground is black - it's shared with the blower motor. Follow it from the blower motor back to the module. Make sure the frame connection is good. I don't think you'll be wasting money on a new module, but since I'm not the one doing the troubleshooting, it's only my best guess - voltage in should give you voltage out.

 

I installed the new module today and it solved the problem. The fan turned on successfully.

Thanks for your help, SunCr.