headaches

Heres one I hope someone can shed some light on.The heater in my 85 comes on under acceleration/load with the selector turned off.I replaced the control valve with no results. This started after replacing the heater core. Any input would be appreciated thank you

Muffin

To get you started, where does the hot air come out? Floor, A?C vents, defroster? Have you removed the vac line from the heater control valve to see if it makes a difference?

headaches

Good morning. It seems to come from the floor mostly and I did try removing and plugging the vacuum line

jhammons01

This sounds like the door is not closing all the way. Under the increased horsepower hot coolant pressurized by the water pump may be forcing it's way past a semi closed door.

Check the linkage, and woe is you if the door has an internal blockage keeping it from closing. You've changed the heater core once.....

Muffin

Not sure how the door system works under the various settings. Guess I best pull out thwe FSM. BUt if he has this happen with the heater control valve unpluged,no vac line. the only way for hot water to circulate is thru a valve stuck open.

headaches, with the car running, have someone move the selector lever to heat, observe what the control valve does. With the car at operating temp one hose3/4 I think should be warm, the other,5/8, should be cold,well cooler. When the valve is opened both should get hot.

jhammons01

What he said!!

Door, Valve......what ever that thing is that shuts off the flow of water when closed.

headaches

Thanks all looks like i will be going in to the heater core again hence the nickname headaches!I have a C5 also would rather work on my vettes than drive anything else !

Muffin

Why are you going into the heater core until you have exhausted all other possibilities? Seems to me the heater core is doing its job, hot water in --heat out. You have to determine how the core is getting hot coolant with the heater in the off position.

headaches

I was going to find the blend door and see if it is stuck.Last night it was coming out all of the vents and it stayed on all the time when it usually will quit after awhile