Weirdest Problem I've ever seen...
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6th Gear
Joined: May 2011
Posts: 6
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Weirdest Problem I've ever seen...
So I have my 87 on a battery charger and everything is going good, the keys are IN MY HOUSE and the car is off. All of a sudden my heater fan starts up??? wtf is going on here? It blows air for a few seconds then cuts out for a few minutes, then starts up again and so on and so on. So at this point I had to unhook the battery cause now its starting on its own randomly and I don't want the garage to go up in flames! I read on a few sites maybe the relay may cause this? Where can I find the relay under the hood? And has anyone else heard of this or have any ideas? Thanks.
Team Owner
Joined: Dec 2000
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From: SE NY
Cruise-In II Veteran
Wow, that IS a new one.
First thing I would check voltage at batt with charger hooked up, both AC V & DC V.
I would also disconnect the - lead and check battery drain with all lights & ign off.
First thing I would check voltage at batt with charger hooked up, both AC V & DC V.
I would also disconnect the - lead and check battery drain with all lights & ign off.
Last edited by 65Z01; Apr 25, 2013 at 03:24 AM.
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From: Overland Park Kansas
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Something along these lines. If you're not aware, the A/C "head unit (aka C68) goes thru a boot-up cycle when the battery is disconnected/reconnected. It's learning the blend door limits (by measuring resistance of the motor that drives the door).
Sounds like that boot-up circuit is trying to activate at the wrong time.
Sounds like that boot-up circuit is trying to activate at the wrong time.
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From: Overland Park Kansas
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No. I'm 99% sure there's no external heater fan relay. The two controls for the Climate control are the head unit and the board above the accelerator pedal. The later doesn't have a relay. (It's pictured on Batee's Corvette website.)
(OTOH, What's a BCM?)
(OTOH, What's a BCM?)
Last edited by GREGGPENN; Apr 25, 2013 at 04:53 PM.
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From: Anaheim CA
The C68 (automatic) HVAC has a control module mounted on the evaporator in the airstream to keep it cool. It controls the fan speed and compressor clutch.
The C60 (manual) HVAC has a set of resistors in that position that control the fan speed. They are bypassed by the fan relay when the fan switch is set to HIGH.
Check this fuse if you have the C68 system. The relay mounts here if you have a C60 system:
The C60 (manual) HVAC has a set of resistors in that position that control the fan speed. They are bypassed by the fan relay when the fan switch is set to HIGH.
Check this fuse if you have the C68 system. The relay mounts here if you have a C60 system:
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From: Overland Park Kansas
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The C68 (automatic) HVAC has a control module mounted on the evaporator in the airstream to keep it cool. It controls the fan speed and compressor clutch.
The C60 (manual) HVAC has a set of resistors in that position that control the fan speed. They are bypassed by the fan relay when the fan switch is set to HIGH.
Check this fuse if you have the C68 system. The relay mounts here if you have a C60 system:
The C60 (manual) HVAC has a set of resistors in that position that control the fan speed. They are bypassed by the fan relay when the fan switch is set to HIGH.
Check this fuse if you have the C68 system. The relay mounts here if you have a C60 system:
I'd forgotten about the alum finned module sitting down inside the evap core!
Is that what's termed the BCM? What's the fuse pictured above for?
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From: Overland Park Kansas
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Ah...thanks. I remember checking that component as part of my diagnostics (trying to figure out a different issue).
Note there is a trick to getting it out of the evap core. Once you remove the screws, it drops down into the core. So, get a handle on it while removing the screws. Otherwise, you'll get standing their cussing and wondering how you'll get it out of the hole!
Note there is a trick to getting it out of the evap core. Once you remove the screws, it drops down into the core. So, get a handle on it while removing the screws. Otherwise, you'll get standing their cussing and wondering how you'll get it out of the hole!
Instructor
Joined: Oct 2010
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From: Rapid City South Dakota
The C68 (automatic) HVAC has a control module mounted on the evaporator in the airstream to keep it cool. It controls the fan speed and compressor clutch.
The C60 (manual) HVAC has a set of resistors in that position that control the fan speed. They are bypassed by the fan relay when the fan switch is set to HIGH.
Check this fuse if you have the C68 system. The relay mounts here if you have a C60 system:
The C60 (manual) HVAC has a set of resistors in that position that control the fan speed. They are bypassed by the fan relay when the fan switch is set to HIGH.
Check this fuse if you have the C68 system. The relay mounts here if you have a C60 system:
Thread Starter
6th Gear
Joined: May 2011
Posts: 6
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The C68 (automatic) HVAC has a control module mounted on the evaporator in the airstream to keep it cool. It controls the fan speed and compressor clutch.
The C60 (manual) HVAC has a set of resistors in that position that control the fan speed. They are bypassed by the fan relay when the fan switch is set to HIGH.
Check this fuse if you have the C68 system. The relay mounts here if you have a C60 system:
The C60 (manual) HVAC has a set of resistors in that position that control the fan speed. They are bypassed by the fan relay when the fan switch is set to HIGH.
Check this fuse if you have the C68 system. The relay mounts here if you have a C60 system:
Last edited by speedy740; Apr 26, 2013 at 09:41 PM.
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That fuse is in the feedback circuit that tells the HVAC control head how fast the blower motor is turning. It's mounted on the firewall next to where the heater hoses go through the firewall to the heater core (you can see the hoses in the picture).
Drifting
Joined: Aug 2006
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From: Canandaigua New York
I had the same problem with my 87.
Would come out to a dead battery and when I hooked up the charger, the blower motor would come on.
I replace the BCM and it's been fine every since.