Deville 67...Heater works only for 2 minutes

[TomB]

Hi all, My deville 67 has an issue with the heater. Car also has A/C (is not filled with gas so is not cooling). But the issue I am grappling with is that when I switch on the heater it blows nicely warm air, but only for 2 minutes, the air gradually gets almost as cold as the outside air. All vacuum lines are connected, radiator is full.

Suggestions are very welcome..

Thanks
Tom (TomB, T.Bakkum)

[TJ Hopland]

If you leave it set for auto and max heat does the blower stay at high and the air still comes out the floor when it gets cool?

Have you tried checking the temp of the hoses in and out of the heater core either by carefully grabbing them or even better with one of those IR temp guns?

Does a 67 have the return from the heater core going directly into the radiator?  If it does and its on the side with the cap you could try lowering the level to below where that hose comes in and then look to see if its flowing.   

I assume a 67 has a water control valve.  Perhaps someone can tell you its location and if its open or closed when it gets a vacuum signal.  Knowing that you could possibly disconnect it or operate it with a manual hand vacuum pump to try and make sure its open.

[cadillactim]

Check for partially plugged heater core. Check like TJ said.

The water valve is normally open, takes vacuum to close it, and that is only in full a/c mode. Make sure valve is open all the way.

Tim

[TomB]

Thanks TJ and Tim, great tips. I assume that water circulation is the issue. Fortunately the core is clean (got it out and had it fixed). The valve is probably the culprit, will work on it. Thanks!!

Tom

[Chopper1942]

Back in the day, it was not uncommon for the rubber inside the hot water shut off valve would swell went it got hot and shut off the water flow to the core.  If the valve is working OK, the hoses on either side of the valve should be hot.  If not the valve is shutting down.  If the inlet hose to the heater core is hot and the outlet hose cold, the core is plugged.  If this is the case, try back flushing the heater core with a garden hose to the outlet with the inlet hose off the core.  See if any junk comes out and you get a good flow of water thru the heater core.