Non functioning HVAC system
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Cadillac Seville / Cadillac Eldorado Forum Discussion, Non functioning HVAC system in Past Cadillac Vehicle Discussion; Hey all, I have a 1997 Eldorado ETC. I picked the car up about a week ago, when I drove ...
  1. #1
    Coldreach is offline Cadillac Owners Member
    Automobile(s): 2001 Eldorado ESC
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    Non functioning HVAC system

    Hey all,
    I have a 1997 Eldorado ETC. I picked the car up about a week ago, when I drove it home the HVAC system worked flawlessly. Today I tried turning it on and nothing happens. I tried using the manual fan controls, turning the AC on and off, disconnecting and reconnecting the battery and fuses but nothing works. When I get 40+ mph the air flow is a little better but nothing like what it should be. There don't appear to be any DTC's relative to this fault. Can anyone give me an idea as to what may be the problem and if there is a solution?

    Thanks,
    Davis

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  3. #2
    N*Caddy's Avatar
    N*Caddy is offline Cadillac Owners Master
    Automobile(s): 1997 Cadillac STS (BOSE w/AUX In, Massage Seats, URPAS, "Z")
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    Re: Non functioning HVAC system

    So your "mode", temperature adjustments, A/C are all working, you are able to change the fan speed on the Climate Control Module (and is displayed correctly) yet the HVAC fan is not responding?

    The HVAC fan connector is located on the right side from the brake master cylinder, is that 3 wire connector just above the HVAC fan.
    The pin-out is like this:
    1. THICK RED wire = Battery supply voltage (hot all the time)
    2. THICK BLK wire = GND
    3. Thin ??? wire = Fan speed control wire.

    So, unplug the connector and you should be able to measure ~12V DC between the 2 thick wires (harness side).
    If you don't then check between RED (THICK) wire and an exposed metal body part or the engine block. If still no power then your ground is missing (check for continuity between BLK wire and exposed metal body part of engine block). If still no voltage between RED wire and GND then you are missing the supply voltage.
    If the voltage between RED and BLK (THICK) wires is present (all the time regardless of the ignition) then turn ignition on, test voltage between the THIN (fan speed control) wire and the BLK (THICK) wire. Should see a voltage between ~3V and ~9V across the fan speed adjustment range where ~3V is fan speed on lowest level and ~9V with fan speed on highest level (you will adjust the fan speed while measuring from your climate control buttons).
    If the control voltage checks out then you are looking at a replacement HVAC fan. If the control voltage doesn't checks out then you are looking at further diagnosis of the climate control module.

    Just so you know the Climate Controls are a bit more complicated that you would expected to be, it involves 2 modules: the Climate Control Module (the thing with the buttons and display underneath the HU) and the Climate Control Programmer located underneath the glove compartment.
    The module that controls ALL the HVAC functions (including your HVAC Fan speed) is the one underneath the glove compartment, the Climate Control Module (the thing with buttons and screen) is nothing but a user interface, it forwards all the commands to the Programmer.
    One thing to pay attention, are the “modes” working (like air deflected to the feet, or feet and central, or just central or the defrost grille)? Is your parking break released when you put it in gear?

  4. #3
    Coldreach is offline Cadillac Owners Member
    Automobile(s): 2001 Eldorado ESC
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    Re: Non functioning HVAC system

    Thank you so much for the reply. I checked the plug for voltage and it seemed fine so I plugged it back and and it worked! I guess the pins just weren't making proper contact.

  5. #4
    Submariner409's Avatar
    Submariner409 is offline If it won't run, slap in a big stereo
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    Re: Non functioning HVAC system

    The parking brake release mentioned in N*Caddy's post - there's a vacuum line that runs through the firewall and T's to supply vacuum to some HVAC functions and the parking brake release diaphragm. I don't know if that changed to electrical in 1998 or in 2000 ............

  6. #5
    N*Caddy's Avatar
    N*Caddy is offline Cadillac Owners Master
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    Re: Non functioning HVAC system

    Not in the Eldorado, still vacuum operated like the rest of the HVAC controls all way up to '02.
    To explain to the OP why I mentioned parking brake is because the vacuum operated items under the dashboard are all controlled from a manifold by the Climate Control Programmer. Generally the stuff under the dashboard (say the blend door) is not so obvious to the regular drivers if is operational or not. Parking brake is the most obvious...if it releases it means 2 things:
    1. You have vacuum supply to the manifold
    2. The Climate Control Programmer is operational. If that one is operational it means the HVAC fan should have the proper controls too.

  7. #6
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Non functioning HVAC system

    Quote Originally Posted by Coldreach View Post
    I checked the plug for voltage and it seemed fine so I plugged it back and and it worked! I guess the pins just weren't making proper contact.
    I assume you are talking about the blower motor? Check the connecter closely. If it is discolored and the pins are burnt, the blower is failing and the resistance is high.

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