AC not blowing with engine running
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AC not blowing with engine running
Hello all! Im having a problem with my AC blowing when the engine is running. Everything works perfectly fine with just the ignition on in accessory mode but as soon as I start the engine, air stops blowing from the vents.
Ive installed a (supposed to be) known good HVAC control panel. Its a new blower motor (TYC) not a GM part. Ive checked powers and grounds and ohmed wiring and everything seems to be good. Its odd though because I have .142 volts on the ground while its working with the engine off. With the engine on, and when it stops blowing air, ground goes to 0.0v
Has anyone ever run into this before, Im kinda at a loss for further diag right now.
car is a 2008 base model c6
Thanks!
Ive installed a (supposed to be) known good HVAC control panel. Its a new blower motor (TYC) not a GM part. Ive checked powers and grounds and ohmed wiring and everything seems to be good. Its odd though because I have .142 volts on the ground while its working with the engine off. With the engine on, and when it stops blowing air, ground goes to 0.0v
Has anyone ever run into this before, Im kinda at a loss for further diag right now.
car is a 2008 base model c6
Thanks!
Last edited by ExoVett; Jul 21, 2024 at 04:05 PM.
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It’s a good idea if you let us know what year the car is at minimum !!…any other info helps too !!…you should ALWAYS suspect new parts if not OEM !!…you can compound your problem with bad “new” parts !!…how did you check ground ??…now was this your original concern that it was blowing only in ACC and not with the engine running or was it not working at all ??
Last edited by C5 Diag; Jul 21, 2024 at 04:05 PM.
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ah, my apologies. Its a 2008 base model c6. Ground was checked with a multimeter
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As I mentioned above was this your original concern that the blower was only working in ACC and not engine running ???…or was the blower not working at all and then you replaced HVAC Module and Blower Motor Control Module ??…Terminal B is PWM !!..I’ll get back a little bit later !!
Last edited by C5 Diag; Jul 21, 2024 at 04:15 PM.
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This is my original concern, the blower only works in acc mode and does not work with the engine running. Blower was replaced because it was missing when I bought the car. I dont know the back story for that but it was a wrecked car when I bought it. Its now bodyless and is a roll cage around the frame. The hvac module was only replaced due to suspicion of being a problem
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This is my original concern, the blower only works in acc mode and does not work with the engine running. Blower was replaced because it was missing when I bought the car. I dont know the back story for that but it was a wrecked car when I bought it. Its now bodyless and is a roll cage around the frame. The hvac module was only replaced due to suspicion of being a problem
Last edited by C5 Diag; Jul 21, 2024 at 07:15 PM.
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Did you check the PWM signal in ACC and engine running ??…with a DVOM it will read differently than using a lab scope…if 50% duty cycle you will maybe 6 volts with a DVOM instead of 12 volts depending on blower speed…I’ll try to get you these voltages with blower on low and high and in ACC and engine running…you always want to checks grounds dynamically or with engine running and not statically…are you back probing each of the wires with connector plugged in ??
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yes, I have been back probing with the connector plugged in. While on the singal wire, low speed shows 10v and as speed is increased, voltage goes down, I forgot what my low speed voltage was but I believe around 5-6v. It is consistent in doing that while in acc as well as engine running
Last edited by C5 Diag; Jul 21, 2024 at 09:30 PM.
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Well I used my DVOM instead of the scope and with the engine running I had 13.13 volts on high speed and 13.50 on low...same readings Ignition ON...I used the door hinge bolt for a good ground and with engine running I had 0.02 volts on low speed and 0.16 volts on high speed for a ground measurement...with Ignition ON (not ACC)...got the same ground readings....you don't measure ground (your 1.42 volts) statically if that’s what you measured...engine must be running or Ignition ON with blower on and then measure ground....check your ground Ignition ON and running and post results....you may have some bad parts like a bad blower motor module.
For ground, with the ignition on, I have 0.013 on low and 0.142 on high.
For ground, with the engine on, I have -0.03 regardless of air speed
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Ignition on (engine off) I have 10.2 volts on low and 4.6 volts on high. Engine on, I have 12.4 volts on low and 7.2 volts on high.
For ground, with the ignition on, I have 0.013 on low and 0.142 on high.
For ground, with the engine on, I have -0.03 regardless of air speed
For ground, with the ignition on, I have 0.013 on low and 0.142 on high.
For ground, with the engine on, I have -0.03 regardless of air speed
MMMM ??…how about trying this…back probe red/black wire with one lead of DVOM and find HVAC fuse 28 in under hood fuse box that supplies its power and place other lead of DVOM on either of the 2 test points of the fuse and run the blower speed from high to low…you are voltage drop testing that circuit and you shouldn’t see more than maybe 0.2 to 0.3 volts at each speed…you may need 2 people for this…if you see negative number on DVOM don’t worry about that…just look at the number…in this case you would just swap the leads around…I’ll check the gray/black PWM wire tomorrow again…really didn’t see a change from high to low speed using PWM and Duty Cycle on my graphing multimeter.
Last edited by C5 Diag; Jul 21, 2024 at 07:55 PM.
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MMMM ??…how about trying this…back probe red/black wire with one lead of DVOM and find HVAC fuse 28 in under hood fuse box that supplies its power and place other lead of DVOM on either of the 2 test points of the fuse and run the blower speed from high to low…you are voltage drop testing that circuit and you shouldn’t see more than maybe 0.2 to 0.3 volts at each speed…you may need 2 people for this…if you see negative number on DVOM don’t worry about that…just look at the number…in this case you would just swap the leads around…I’ll check the gray/black PWM wire tomorrow again…really didn’t see a change from high to low speed using PWM and Duty Cycle on my graphing multimeter.
That was with ignition on and engine off. With the engine running, 0.0 and no change with speed
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OK, so no issue of voltage dropping between the fuse and Module…let me do some testing on mine tomorrow with my scan tool.
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I disconnected the module connector and front probed the control wire…all I saw whether the ignition was on or engine running was .5 volts on low speed and .9 volts on high speed…I thought it may have been an HVAC fuse in the IPC fuse block which is only powered with the engine running but no luck…see if you have system voltage on the red/black wire with ignition on or running…I was reading my usual 14.25 volts….with what I’m seeing hard to say whether it’s a bad HVAC Module or Blower Module…I’ll further research this a little later.
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I disconnected the module connector and front probed the control wire…all I saw whether the ignition was on or engine running was .5 volts on low speed and .9 volts on high speed…I thought it may have been an HVAC fuse in the IPC fuse block which is only powered with the engine running but no luck…see if you have system voltage on the red/black wire with ignition on or running…I was reading my usual 14.25 volts….with what I’m seeing hard to say whether it’s a bad HVAC Module or Blower Module…I’ll further research this a little later.
I ordered a factory GM blower this morning and am currently trying to local a new or confirmed good HVAC panel.
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when referring to red/black wire, youre talking about pin A to the blower motor, correct? If I remember correctly, I always had source voltage on that wire but will confirm when I get home tonight.
I ordered a factory GM blower this morning and am currently trying to local a new or confirmed good HVAC panel.
I ordered a factory GM blower this morning and am currently trying to local a new or confirmed good HVAC panel.
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it looks like Ive got it working now, guess I wont be cheaping out on aftermarket parts anymore. My new friend at GMC kindly loaned me a factory blower motor and it seems to have resolved my problem. Its not fully mounted back up in the car yet, just plugged in but its working now with the engine running!
thanks for all your help!
thanks for all your help!
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it looks like Ive got it working now, guess I wont be cheaping out on aftermarket parts anymore. My new friend at GMC kindly loaned me a factory blower motor and it seems to have resolved my problem. Its not fully mounted back up in the car yet, just plugged in but its working now with the engine running!
thanks for all your help!
thanks for all your help!
Cool !!…so much for JUNK aftermarket parts !!…OEM for the win !!