04 Regal HVAC and Cruise Control don't work

Jin42Jin42 Member Posts: 6
edited May 2022 in Buick
When I turn the fan speed down all the way the Cruise light comes on. I can hear compression/decompression when changing the vent setting still, but no air comes out of the vents on any setting.

Possible fan relay or fuse issue I'm guessing, but thought the involvement of the cruise was weird and wanted to inquire about it since it may be something bigger... Haven't looked at all the fuses in the dash fuse box yet.

Any feedback appreciated, thanks.


  • thecardoc3thecardoc3 Member Posts: 5,599
    Troubleshoot the cooling fan operation first. Does this have an automatic HVAC system or a manual system? The cruise lamp is controlled by the instrument cluster via digital communication. It may help to first get a better idea of what is wrong with the blower operation and then deal with the cruise lamp if necessary.
  • Jin42Jin42 Member Posts: 6
    edited May 2022
    It's a manual system. I'm taking the dash apart in a few days to put in a different receiver deck.. Planning to work with it more then.
  • Jin42Jin42 Member Posts: 6
    Alright, so I tried recharging the AC but the pressure seemed too high and wouldn't take it despite bypassing the AC clutch relay and getting the clutch to engage. The AC recharge gauge only showed 25-30 PSI also. AC Clutch doesn't engage without relay bypass

    I was able to get the blower to turn on connecting it directly to the battery but I found the blower resistor module and the blower itself to be in a pretty worn and somewhat rusted condition so I replaced both and still cant get the blower to turn on.

    I've pulled all the fuses in the primary and secondary fuse boxes that seem related and none of them were burned. I also swapped the AC Clutch relay with another of the same model.

    When it started having issues it would work and then stop working for a while and then start up again the next time I drove it. Now it doesn't work at all. So I thought maybe the ac charge depleted and eventually shut down the compressor clutch.

    Also found 12V at the fan switch on one of the seven contacts in the plug, but when re-installed on the switch then voltage tested at the resistor output harness that connects to the blower, all of the switch setting (six) only read 3.6 volts with a new resistor in place. The old resistor read 4.0 volts . wondering if there is something mid way between the fan switch and the resistor that could be amiss.
  • Jin42Jin42 Member Posts: 6
    Tested the seven pin connector at the resistor module, found 12V on the end pin, will test again to see if the hot pin moves to the other pins when fan switch is moved to higher speeds. Still can't figure out why there is 12v into the resistor module, but only 4v out to the blower...both the old module and the new one read the same.
  • thecardoc3thecardoc3 Member Posts: 5,599
    A lot of people undervalue electronics training especially in relation to auto repair and becoming a competent technician.

    I have attached a section of the wiring schematic for the manual AC system. I notated the wires where power for high speed blower operation as well as the lower speed operation are.

    The blower resistor assembly is in the middle on the left hand side. If you look you will see the power for the lower speeds comes in on the brown wire and then goes to the HVAC blower switch. From there the switch connects that 12v power to one of the resistor connections in the blower resistor.

    We stress understanding ohms law, not so much that the technicians have to sit there and do math problems but at least enough for them to understand that when current is flowing in a circuit and that current encounters a resistance a voltage drop will occur. If you follow the yellow wire from the HVAC blower switch to the resistor, with the blower switch set to low speed, you should see 12v at the blower resistor and then as the current flows through each resistor the voltage measured would drop until you get to the lowest voltage that would be fed to the blower motor on the purple wire.

    Then important thing to remember to get a voltage drop, there must be current flowing. A single open in the circuit will stop all current flow and you would measure 12v right up to where the circuit is open and then 0v from that point.

    Using the schematic here write down what voltage you measure at the blower resistor for the yellow, then the tan, light blue, and purple wires (terminals A, B, C, and D) with the key on and the blower set to the lowest speed and then post your results.

  • Jin42Jin42 Member Posts: 6
    After additional research I've found various accounts that show identical symptoms and state the issue is the ignition switch. I've ordered a replacement. Should have it in by Wednesday.
  • thecardoc3thecardoc3 Member Posts: 5,599
    Jin42 said:

    After additional research I've found various accounts that show identical symptoms and state the issue is the ignition switch. I've ordered a replacement. Should have it in by Wednesday.

    An ignition switch "could be" bad. If it is then you would measure less than 12v on the brown wire referenced in the schematic above. You would also measure less than 12v on the other wires as described as you move the blower control knob to connect to them. By testing first you avoid replacing a part that might not be "the problem".
  • Jin42Jin42 Member Posts: 6
    It ended up being the ignition switch. everything is working.

    Thanks for taking the time to post.
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