HVAC vacumm on 87 corvette
09-11-2013, 10:10 AM
#1
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HVAC vacumm on 87 corvette
Where does HVAC vacumm originate on 87 corvette engine. There is no vacumm at the vaucumm tank, the HVAC, or the cruise control on my 87 corvette. 2 way check valve is good.
09-11-2013, 10:22 AM
#2
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HVAC line is at the back, passenger side of the intake. Goes to a check valve under or near the distributor, then goes into a bundle of wires that goes through the firewall. It is separate from the cruise and the big ball. I will have to go look at the car for that.
09-12-2013, 01:01 AM
#3
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On the passenger side rear of the plenum there are two vacuum ports. The front one goes to the A.I.R. pump valves and the fuel pressure regulator. The rear port goes to the vacuum check valve next to the distributor. From there it splits and one side goes inside the cabin and operates the HVAC door actuators. The other side goes to the cruise control and the vacuum reservoir.
There should be a vacuum diagram on the radiator shroud that looks more or less like this (note the "TO HVAC"):
There should be a vacuum diagram on the radiator shroud that looks more or less like this (note the "TO HVAC"):
Last edited by Cliff Harris; 09-12-2013 at 01:04 AM.
09-12-2013, 06:28 AM
#4
Is there vac at the check valve?
If not check the line to the intake port
If there is vac present ; then you have a break in the line(s) downstream of the valve.
Is common for the vac line to the HVAC inside to break off flush where it enters the main wiring harness on the firewall behind the dist ,requiring opening up of the harness to extract the broken end for reconnection
If not check the line to the intake port
If there is vac present ; then you have a break in the line(s) downstream of the valve.
Is common for the vac line to the HVAC inside to break off flush where it enters the main wiring harness on the firewall behind the dist ,requiring opening up of the harness to extract the broken end for reconnection
09-17-2013, 04:46 PM
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Thanks for the info and diagram. The one on my vette is missing. The two ports on the passengerside plenum on mine both combine into a single line and go to the air pump valves. One port on the 2 way check valve goes to the vacuum tank, one to the interior of the car, and the other to the fuel regulator. there is no vacuum at all in these lines since it is not connected to a vacuum anywhere.someone really got this wrong when they hooked the lines back up after working on the engine and some point. I tapped into the port at the back of the plenum to the 2 way check valve and now the cruise control and air in the car work as they should. I'll have to rearange the lines so they are correct to the diagram you supplied. Thanks again.