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Help! HVAC not blowing air at any setting

DS75

Member
Joined
Dec 31, 2010
Messages
15
Location
Millersville, MD
Corvette
1986 Coupe, Auto, Metallic Red
Hi - I have an 86 coupe and am new to the forum. Recently my HVAC system stopped blowing air. The car has an electronic control module (possible rebuilt/refurbed). I don't know if it's the C60 or C68 that I have seen referenced in the forum. The temp control seems to work fine, though it's hard to tell when all you get is a faint whisper of air coming through the ducts.

I am asking how to diagnose the problem to minimize the amount of money I throw at parts. I have some basic tools and a voltmeter but no code scanner. What I have done so far is:
  • Removed the ECM and cleaned the contacts and verified the connector harness is ok. I didn't see any burn outs or smell any smoke on the ECM components. It works a little funny, i.e. when I press increase on the fan speed it sometimes takes a few button presses to get it to work. It also used to occascionally go lights out but that has seemed to have gone away since the cleaning
  • All fuses in the dash are ok
  • What I think is the blower motor fuse (5A I think) located next to the blower motor look fine
Based on other threads/posts I suspect the blower motor control module (though I am still suspect of the ECM). Is there a way to verify if either of these are the culprit? I have not checked the blower motor itself yet, nor cleaned the evaporator as I've seen suggested (mainly because I don't know how yet). I am presently waiting for my shop manual to arrive.

Any and all suggestions are welcome. This is my daily driver and its getting cold without the heat in the mornings, plus I'd like to be able to defrost my window. Thanks.
 

gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,547
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Hi - I have an 86 coupe and am new to the forum. Recently my HVAC system stopped blowing air. The car has an electronic control module (possible rebuilt/refurbed). I don't know if it's the C60 or C68 that I have seen referenced in the forum. The temp control seems to work fine, though it's hard to tell when all you get is a faint whisper of air coming through the ducts.


I am asking how to diagnose the problem to minimize the amount of money I throw at parts. I have some basic tools and a voltmeter but no code scanner. What I have done so far is:
  • Removed the ECM and cleaned the contacts and verified the connector harness is ok. I didn't see any burn outs or smell any smoke on the ECM components. It works a little funny, i.e. when I press increase on the fan speed it sometimes takes a few button presses to get it to work. It also used to occascionally go lights out but that has seemed to have gone away since the cleaning
  • All fuses in the dash are ok
  • What I think is the blower motor fuse (5A I think) located next to the blower motor look fine
Based on other threads/posts I suspect the blower motor control module (though I am still suspect of the ECM). Is there a way to verify if either of these are the culprit? I have not checked the blower motor itself yet, nor cleaned the evaporator as I've seen suggested (mainly because I don't know how yet). I am presently waiting for my shop manual to arrive.

Any and all suggestions are welcome. This is my daily driver and its getting cold without the heat in the mornings, plus I'd like to be able to defrost my window. Thanks.
Have you Checked and Cleaned ALL Body/Chassis GROUNDS?~??
If Not,That would be a excellent start!~!!
More than 90% of the time with these cars,I find High Resistance or Non Existent Grounds causing most electronics problems!~!!:thumb:thumb:thumb
 

DS75

Member
Joined
Dec 31, 2010
Messages
15
Location
Millersville, MD
Corvette
1986 Coupe, Auto, Metallic Red
Have you Checked and Cleaned ALL Body/Chassis GROUNDS?~??
If Not,That would be a excellent start!~!!
More than 90% of the time with these cars,I find High Resistance or Non Existent Grounds causing most electronics problems!~!!:thumb:thumb:thumb

Thanks GMJunkie - I'll check them next. Since I don't have a wiring diagram and I imagine there are plenty, any suggestions of known grounds with a high probability of getting fouled/loosened?
 

gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,547
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Thanks GMJunkie - I'll check them next. Since I don't have a wiring diagram and I imagine there are plenty, any suggestions of known grounds with a high probability of getting fouled/loosened?
Back of engine usually 2nd bolt up on Bell Housing,Above the Oil Filter on Block,Behind the battery on frame rail,by radiator support (Lt side),RT and LT frame rail below H/L assys,Below Heater/AC housing on Rt Frame rail,Behind left rear wheel on Lt Rear frame rail,Theres a few on the inside too under trim pieces,But on a 86,I just can't remember exactly where!! A good place to look would be behind Rt and Lt Kick panels and under trim on Halo Panel steel reinforcement, and there may be one under console on steel floor pan too!:)

:beer
PS Pull the blower fan out and make sure a mouse hasn't built a home in your housing blocking air flow!!:D
 

Schrade

Well-known member
Joined
May 2, 2009
Messages
1,315
Location
Not in CF; BANNED!!!
Corvette
'90 LT 5
Welcome onto the boards there.

For an '86, get the FSM - if you're keeping the car. It is a MUST HAVE. Even if you don't do your own wrenching, just KNOWING what's in it will reduce the snowjobs at the shop...
 

boomdriver

Well-known member
Joined
Dec 18, 2008
Messages
1,888
Location
texas
Corvette
87 z-51
Hi - I have an 86 coupe and am new to the forum. Recently my HVAC system stopped blowing air. The car has an electronic control module (possible rebuilt/refurbed). I don't know if it's the C60 or C68 that I have seen referenced in the forum. The temp control seems to work fine, though it's hard to tell when all you get is a faint whisper of air coming through the ducts.



I am asking how to diagnose the problem to minimize the amount of money I throw at parts. I have some basic tools and a voltmeter but no code scanner. What I have done so far is:
  • Removed the ECM and cleaned the contacts and verified the connector harness is ok. I didn't see any burn outs or smell any smoke on the ECM components. It works a little funny, i.e. when I press increase on the fan speed it sometimes takes a few button presses to get it to work. It also used to occascionally go lights out but that has seemed to have gone away since the cleaning
  • All fuses in the dash are ok
  • What I think is the blower motor fuse (5A I think) located next to the blower motor look fine
Based on other threads/posts I suspect the blower motor control module (though I am still suspect of the ECM). Is there a way to verify if either of these are the culprit? I have not checked the blower motor itself yet, nor cleaned the evaporator as I've seen suggested (mainly because I don't know how yet). I am presently waiting for my shop manual to arrive.

Any and all suggestions are welcome. This is my daily driver and its getting cold without the heat in the mornings, plus I'd like to be able to defrost my window. Thanks.

Elect a/c is opt-68.
First, if the buttom seems to work after having to push several times, it sounds like a failed circuit board or possibly LOOSE. The control head comes apart in 3 sections. Remove, pull the face panel off, observe the contacts and clean, then pull the horizontal card out of the shell. Do the same, clean the contacts.
If that does not help, the board is probably bad. They can be rebuilt for $150 exchange.

If thru some form of diagnosis leads you to believe that the control head is OK, then the only other thing that can cause the fan to not come up/on is the Bower Control Module. This is mounted in the top of the evaporator and has to plugs in the top. This part is not repairable and cannot be tested. It gets replaced when symptoms indicate the part has failed. Symptoms like yours.
Does your compressor clutch engage? if not, see the BCM. If the fan will not come on, or comes on slow, see the BCM.
Also check the plug to the blower motor. Those are famous for frying the contacts and running the fan slow. Blower motor $50 or less.

The good news is that the C-68 has a built in diagnostic system thats displayed thru the control head display. Your FSM will describe how to do this.
my best guess...either a control head (panel) or the BCM. Blower motor plug too...turn the system on and wiggle the blower motor plug to see if that has an effect,. if not, use a jumper wire to apply voltage to the blower. If it runs, the motor is no longer suspect,. go back to the BCM.

When a BCM fails, that has no effect on the control panel.

If the control panel fails, the display will flash, be in greek, not respond to buttons etc. A bad motor will show normal display with no fan results.
 

DS75

Member
Joined
Dec 31, 2010
Messages
15
Location
Millersville, MD
Corvette
1986 Coupe, Auto, Metallic Red
Elect a/c is opt-68.
First, if the buttom seems to work after having to push several times, it sounds like a failed circuit board or possibly LOOSE. The control head comes apart in 3 sections. Remove, pull the face panel off, observe the contacts and clean, then pull the horizontal card out of the shell. Do the same, clean the contacts.
If that does not help, the board is probably bad. They can be rebuilt for $150 exchange.

If thru some form of diagnosis leads you to believe that the control head is OK, then the only other thing that can cause the fan to not come up/on is the Bower Control Module. This is mounted in the top of the evaporator and has to plugs in the top. This part is not repairable and cannot be tested. It gets replaced when symptoms indicate the part has failed. Symptoms like yours.
Does your compressor clutch engage? if not, see the BCM. If the fan will not come on, or comes on slow, see the BCM.
Also check the plug to the blower motor. Those are famous for frying the contacts and running the fan slow. Blower motor $50 or less.

The good news is that the C-68 has a built in diagnostic system thats displayed thru the control head display. Your FSM will describe how to do this.
my best guess...either a control head (panel) or the BCM. Blower motor plug too...turn the system on and wiggle the blower motor plug to see if that has an effect,. if not, use a jumper wire to apply voltage to the blower. If it runs, the motor is no longer suspect,. go back to the BCM.

When a BCM fails, that has no effect on the control panel.

If the control panel fails, the display will flash, be in greek, not respond to buttons etc. A bad motor will show normal display with no fan results.

Boomdrive - Thanks.

I pulled the control head again and looked at it. It is a "Factory Authorized Remanufactured Module". The horizontal board looks good and I re-cleaned the contact there to the front panel and the wiring harness at the back. The front panel won't seperate - it's a one piece molded plastic part with a PCB snapped on. It doesn't appear it will come off without damaging the PCB. My FSM should ship in a day or so, so I think I'll wait to try the diagnostics when it gets here. Some of the control head functions are definitely working right though - I can see down the ducts and watch parts move when I select bi-level vs heat vs defroster.

I checked the plugs to the BCM and they are clean and not fried. When I turn on the fan from the control head I do here a click that sounds like a solenoid. I did try jumping the blower motor to 12VDC/Batt and it ran full force. I did try wiggling the BCM wiring harnesses but no luck there (same for the blower motor power wires).

At this point I'm leaning towards the BCM but I'll wait to check the control head diagnostic codes before ordering a BCM.
 

boomdriver

Well-known member
Joined
Dec 18, 2008
Messages
1,888
Location
texas
Corvette
87 z-51
Boomdrive - Thanks.

I pulled the control head again and looked at it. It is a "Factory Authorized Remanufactured Module". The horizontal board looks good and I re-cleaned the contact there to the front panel and the wiring harness at the back. The front panel won't seperate - it's a one piece molded plastic part with a PCB snapped on. It doesn't appear it will come off without damaging the PCB. My FSM should ship in a day or so, so I think I'll wait to try the diagnostics when it gets here. Some of the control head functions are definitely working right though - I can see down the ducts and watch parts move when I select bi-level vs heat vs defroster.

I checked the plugs to the BCM and they are clean and not fried. When I turn on the fan from the control head I do here a click that sounds like a solenoid. I did try jumping the blower motor to 12VDC/Batt and it ran full force. I did try wiggling the BCM wiring harnesses but no luck there (same for the blower motor power wires).

At this point I'm leaning towards the BCM but I'll wait to check the control head diagnostic codes before ordering a BCM.

Its the BCM...

I've been up/down this road several times with the opt 68 and I can tell you with certainty, that the system IS less complicated than it would seem !

There are only 3 working sections of the system...

1. control head (panel) directs the signals
2. BCM directs power supply to blower/clutch
3. Programmer (little vent dammit that you never want to fool with)

All three of these parts combine to generate the computer style control for the a/c vents, compressor and cabin temp.

Everything else is just parts. Often the BCM will fail and the blower won;t turn off, even with the key out of the ignition. Or the clutch won't engage...it has weird effects of the different related parts of the system.

The cooling fan switches/low pressure/high pressure/clutch are a little confusing at first but in reality they are just a long loop.

The most common problem with the opt 68 is that everyone OVERTHINKS it to death and ends up looking at longshots. It really is a simple a/c management system. If the control head seems to have the right display and operates the vents, then the board is likely ok. That front panel is glued together with the edge lock that you see and its just a display board. If the main board contacts are good, its probably a good control head. Those contacts get loose sometimes. The easiest way to tighten them is to add a strip of tape to the back side of the contacts to snug them up in the reciever.

Shop around for the BCM. The local auto parts price can vary from $75 to $200.
I have never heard of a sure way to test a BCM, So I would beware used ones unless they have a return policy.

Oh yeah,
at some point it would be a good idea to do as the GMjunkie suggest and clean and inspect the grounds. Being a plastic car thats computer controlled, there is a ground somewhere near every electrical system servo or control....all over the car. The most interesting ones are on the trans where he describes. a set of 5 on one bolt that you can;t live without. Grounds are how everything is controlled and how the power route is managed.
 

vetteoz

Well-known member
Joined
Jan 20, 2004
Messages
1,564
Location
Not in Kansa anymore
Corvette
1990
I checked the plugs to the BCM and they are clean and not fried. I did try jumping the blower motor to 12VDC/Batt and it ran full force. I did try wiggling the BCM wiring harnesses but no luck there.
Check for 12V on the heavy red wire at BCM.
May have blown the fusible link that supplies power through BCM to the blower motor
 

John Robinson

Gone but not forgotten
Joined
May 3, 2005
Messages
1,555
Location
Muncie, Indiana
Corvette
1993 Polo Green Coupe
Pull the blower motor and see if the fan turns freely. While you have it out hot wire it directly to the battery. On mine I had a corroded shaft on the motor and after I lubricated it and ran it from the battery it has worked fine. When the blower is in the car and hooked up to the heater wire harness it does not get the full 12 volts. So when it tries to start the motor it does not have enough torque to get it to spin. If you find the blower is bad you have done half the work to replace it and they are not that expensive.:upthumbs

Just as Junk said Mickey and his friends seem to like to build there homes in places like these. You might also look at the fresh air intake to be sure it is not blocked
 

vetteoz

Well-known member
Joined
Jan 20, 2004
Messages
1,564
Location
Not in Kansa anymore
Corvette
1990
Pull the blower motor and see if the fan turns freely. While you have it out hot wire it directly to the battery.
He does say above
" I did try jumping the blower motor to 12VDC/ Batt and it ran full force."
which would indicate problem is with power supply to motor
 

John Robinson

Gone but not forgotten
Joined
May 3, 2005
Messages
1,555
Location
Muncie, Indiana
Corvette
1993 Polo Green Coupe
He does say above
" I did try jumping the blower motor to 12VDC/ Batt and it ran full force."
which would indicate problem is with power supply to motor

OK you got me there but I still would pull the blower motor and look for a blockage. MY daughter visited me last summer and when she got here from NH she said her air conditioning was not working. I bought a fresh air filter and when I pulled the old one out I retrieved a 5 gallon bucket of nesting material from the duct work. so I guess the question I have is does he hear the blower running when he uses his heater or air. If so then I would do again as first suggested by Junk and look for the blockage. It goes without saying that if the blower motor is not running there may be a problem in the electrical circuit. You notice I said may be because if there is something restricting the blower then it won't run with the very low voltage from the circuit board on start up. That is not to say that if you put 12 volts directly to it may run. I still think that it is worth the 10 to 15 min. needed to pull the blower motor. I only am raising this possibility because in my experience with my Corvette most of the problems have been things that have not required the use of new parts to fix. I am a cheapskate and try to work my way through my problems. Yes you all may be right in what you have experienced and fixed on your cars and I may be lucky that I have not had those kind of problems. So please don't take what I say as being critical of what you have offered to this new poster but rather just another voice trying to relay his experience and help from my perspective.
 

vetteoz

Well-known member
Joined
Jan 20, 2004
Messages
1,564
Location
Not in Kansa anymore
Corvette
1990
So please don't take what I say as being critical of what you have offered
No offense taken

I am reading between the lines here and taking his comment
"it ran full force "
to mean he was happy with the airflow from the vents when motor powered direct from battery which would eliminate any blockages in the ducting ?
If he only meant the blower motor ran at full speed then I would consider your scenario a possibility
 

boomdriver

Well-known member
Joined
Dec 18, 2008
Messages
1,888
Location
texas
Corvette
87 z-51
No offense taken

I am reading between the lines here and taking his comment
"it ran full force "
to mean he was happy with the airflow from the vents when motor powered direct from battery which would eliminate any blockages in the ducting ?
If he only meant the blower motor ran at full speed then I would consider your scenario a possibility

Its pretty darn difficult to plug up the evap air passages to the blower from the outside intake ducts...
I recently changed blowers and took a good look inside since I had a damaged screen above...
yes, there was a good handful of leaves and various debris stuck in the EDGES of the evap air passage where its designed to collect. The portion where air actually passes for diversion inside is so small and so arranged that its difficult for anything to get stuck there, it all goes to the edges where there is sufficient gap. Baffles and bends help collect junk at that point so that it does not enter the cabin and exit the vents.

I have to imagine that the engineer that designed the induction system understood that unfiltered air might be dirty or leaves might get sucked in, and designed the ducts accordingly. Filters for cabin air were unheard of until a few yrs ago.
 

John Robinson

Gone but not forgotten
Joined
May 3, 2005
Messages
1,555
Location
Muncie, Indiana
Corvette
1993 Polo Green Coupe
I hope DS75 will post the final results to his problem so we can all learn from it.

Having said that I think it is time for me to disappear before I say something that might not be appropriate to this forum and let it get back to offering information to help DS75 with his inquiry.:z
 

DS75

Member
Joined
Dec 31, 2010
Messages
15
Location
Millersville, MD
Corvette
1986 Coupe, Auto, Metallic Red
Issue Resolved

Last night I got the blower motor control module and put it in. For those wondering the best price I found was $149 with free shipping. If anyone has a list of online vendors they use for C4 parts please share. I was having trouble finding sites who had it given it seems this is a part that fails fairly commonly. Maybe I just missed them in my searches. I looked on Ecklers, autowarehouse.com, corvette central, mid america motorworks to name a few. Seems most sites focus on either performance parts to improve speed/handling or parts to make your vette prettier. In the near future I'm more interested in parts that keep my vette running.

Anyway, as we went through in earlier posts the blower control module seemed the most likely culprit (fuses, motor, and control head were all ok/functioning) and that was it. I swapped parts and had full use of the blower motor. Not a day to soon either as I woke up to an inch of snow on the car this morning. Thanks for your help everyone. Now on to the next 20 items on my fix-it list.
 

DS75

Member
Joined
Dec 31, 2010
Messages
15
Location
Millersville, MD
Corvette
1986 Coupe, Auto, Metallic Red
Where did you find the part?
I got it from autopartswarehouse.com. At the time of ordering they had the best price. I also ran a google search for coupons for that site and found a few that were applicable. I may have been able to for other sites as well but didn't since autopartswarehouse.com was the cheapest to start with (of the sites I found with the part).

It was an AC/Delco part.
 

boomdriver

Well-known member
Joined
Dec 18, 2008
Messages
1,888
Location
texas
Corvette
87 z-51
I got it from autopartswarehouse.com. At the time of ordering they had the best price. I also ran a google search for coupons for that site and found a few that were applicable. I may have been able to for other sites as well but didn't since autopartswarehouse.com was the cheapest to start with (of the sites I found with the part).

It was an AC/Delco part.
Check the local auto parts stores...thats NOT an exclusive part to a Corvette. Elect a/c is on other GM and has been on Caddys since the 80's. Every parts stores carrys one or can get one within 24 hrs.

Glad that solved the problem.
 

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