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Old 12-16-2012, 01:02 PM   #1
JimPell
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Heater Control Valve

Hi
Does anybody out there know where the vacuum line on the heater control valve goes through the firewall,not getting any vacuum and any suggestions on how to get to it? This is on 87 corvette
Thanks Jim

Last edited by JimPell; 12-16-2012 at 01:12 PM. Reason: Add more
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Old 12-16-2012, 03:30 PM   #2
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It goes through the bulkhead that the wiring harness goes through on the pass side behind the head. You can get to the inside from under the dash there is no good way to get to it and it is a pain in the ass.
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Old 12-16-2012, 03:49 PM   #3
JimPell
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Originally Posted by raidmagic View Post
It goes through the bulkhead that the wiring harness goes through on the pass side behind the head. You can get to the inside from under the dash there is no good way to get to it and it is a pain in the ass.
Thanks.I 'm going to have a hell of time,pretty big.
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Old 12-16-2012, 09:39 PM   #4
87vette81big
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Quote:
Originally Posted by JimPell View Post
Thanks.I 'm going to have a hell of time,pretty big.
Does your 1987 C4 Vette have the C68 Digital display automatic climate control ?
Or do You have the standard manual twist controls for the HVAC functions & blower motor speeds ?

The C68 1986 to 1989 Corvettes had a underdash solenoid circuit board for all HVAC functions.
Electric over engine vacuum functional control.
If you have the C68 system, check for engine vacuum input source to this solenoid vacuum control circuit board.
An old vacuum gauge or Mighty Vac vacuum tester would be helpful making your own troubleshooting checks.

If the control head is dead, cleaning switch contacts & connector don't bring it back to life,
each year of early C4 C68 system control head has its own part # for service replacement.
& its different control heads from a Coupe & Convertible per model year.
To verify this fact, take a look at the driver's & passenger mirror on your 1987. Does it have the small glass etched symbol for heated mirrors?

My 1987 Vert does have the heated mirror symbols on each.
That is difference, extra NPN transistor or SCR - silicone controlled rectifier in C68 control head to turn on heated mirrors with HVAC front windshield defroster turned on for models with heated mirrors.
Heated mirrors only used on early C4's Verts with C68 HVAC option.

BR
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Old 12-17-2012, 10:17 AM   #5
JimPell
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Heater control valve

Quote:
Originally Posted by 87vette81big View Post
Does your 1987 C4 Vette have the C68 Digital display automatic climate control ?
Or do You have the standard manual twist controls for the HVAC functions & blower motor speeds ?

The C68 1986 to 1989 Corvettes had a underdash solenoid circuit board for all HVAC functions.
Electric over engine vacuum functional control.
If you have the C68 system, check for engine vacuum input source to this solenoid vacuum control circuit board.
An old vacuum gauge or Mighty Vac vacuum tester would be helpful making your own troubleshooting checks.

If the control head is dead, cleaning switch contacts & connector don't bring it back to life,
each year of early C4 C68 system control head has its own part # for service replacement.
& its different control heads from a Coupe & Convertible per model year.
To verify this fact, take a look at the driver's & passenger mirror on your 1987. Does it have the small glass etched symbol for heated mirrors?

My 1987 Vert does have the heated mirror symbols on each.
That is difference, extra NPN transistor or SCR - silicone controlled rectifier in C68 control head to turn on heated mirrors with HVAC front windshield defroster turned on for models with heated mirrors.
Heated mirrors only used on early C4's Verts with C68 HVAC option.

BR
One mirrow has the symbol the other does not someone must have changed mirrows.My controls on the dash are push button.Numbers read out on the screen.My vacuum line on the heater control valve has no vacuum and the vacuum line goes down into a harness with a bunch of wires,do you have any idea how to get to the place where it goes through the firewall,looks like it enters right under the distributer,do you have to pull the distributer to get to the harness and some working room.I can't see how it makes the 90 degree turn to go through the firewall being the plastic is so briddle.Have to overlook the spelling,at 73 yrs. old I forget.

Thanks Jim

Last edited by JimPell; 12-17-2012 at 10:21 AM. Reason: Spelling
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Old 12-17-2012, 08:51 PM   #6
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Quote:
Originally Posted by JimPell View Post
One mirrow has the symbol the other does not someone must have changed mirrows.My controls on the dash are push button.Numbers read out on the screen.My vacuum line on the heater control valve has no vacuum and the vacuum line goes down into a harness with a bunch of wires,do you have any idea how to get to the place where it goes through the firewall,looks like it enters right under the distributer,do you have to pull the distributer to get to the harness and some working room.I can't see how it makes the 90 degree turn to go through the firewall being the plastic is so briddle.Have to overlook the spelling,at 73 yrs. old I forget.

Thanks Jim
I am going have to open the hood & crawl under the dash with a flashlight of my 87 Vert to get a better look of where that vacuum line runs exact to the Hot Water Heater shut off valve.
I have a 87 GM FSM Corvette Service Manual too.

Give a night or 2 to get back to You.
Working daytime & have been working on a few of my other cars at night last few weeks.

Not the easiest of cars to work on under the dash & Heater box area.
Might be real tough on your body at 73.
Be rough on a 18 year old too.

Brian
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Old 12-18-2012, 07:20 AM   #7
JimPell
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heater

Quote:
Originally Posted by 87vette81big View Post
I am going have to open the hood & crawl under the dash with a flashlight of my 87 Vert to get a better look of where that vacuum line runs exact to the Hot Water Heater shut off valve.
I have a 87 GM FSM Corvette Service Manual too.

Give a night or 2 to get back to You.
Working daytime & have been working on a few of my other cars at night last few weeks.

Not the easiest of cars to work on under the dash & Heater box area.
Might be real tough on your body at 73.
Be rough on a 18 year old too.

Brian
Can't thank you enought seems like your the only one that knows anything about the heater control valve.I have a FSM but can not find anything about the vacuum line routing.Just got the manual yesterday might be something in there.I was wondering if the vacuum line is one piece or does it tee off where it goes through the firewall.Wonder why they run it through the harness with all the wires? I'm going to try to get a diagram off all the routing of the vacuum lines,probably all are in bad shape,I'm sure somebody has a copy of them.You can be sure I will not route the vacuum line through the harness as long as I have drill bits.
Thanks again
Jim
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