Intermittent No Heat Problem
 

Hoping someone has a suggestion re an intermittent no-heat problem on my 2005 Pontiac Montana SV6 van.

Symptoms (intermittent):
1. No heat coming from the vents. No heat means no heat--air is blowing cold, not even slightly warm.
2. Temp gauge on the dash appears normal. After driving for 15 mins, the needle is just below half.
3. Upper rad hose feels very warm and compressible when engine is hot.
4. Can't be sure, but no heat seems more likely to happen when the temp outside is very cold. At milder temps, it seems less likely to malfunction, which means that the air is blowing hot.
5. Cabin filters are clean.
6. Coolant level seems fine. (There's extra in the overflow tank.)

Is it possible that it's a thermostat? If it was stuck open, I wouldn't expect my temp gauge to look normal, and if it was stuck shut, I'd expect the engine to overheat??

Thanks for any suggestions you can give.

Wayne

probably the actuator for the heat mixer. though i have never worked on a minivan. but there has got to be an actuator of some sort either electric or vacuum that changes from hot to cold, should be able to see it working or not working under the dash

Yes sounds like when you rotate from cold to hot the blend door is not closing.
That being said, it would not hurt to do a rad pressure test to ensure system is able to maintain pressure & there are no leaks or air entering the system.

A bit more information: This morning it was again very cold (-26C) and I couldn't get any heat until we had driven with four people in van for 30 mins. At the beginning of our trip, the fan was on with heater in defrost setting, but air was blowing cold thru the lower dash vents. About 30 mins into the trip (and 15 mins after engine hot), the defrost started to work and the air stopped blowing thru the lower dash vents (with same control settings).

If this is an actuator that's under the dash, I'm surmising that as the cabin begins to warm, the actuator starts to work?? So as a short-term fix to get me thru the next few days until I can get it fixed, I'm thinking I'll use an interior heater to warm the cabin before I start the engine in the morning. Or will that even help?

How hard is it to repair a bad actuator?

Thanks for the help.

Wayne

I have tried to find diagrams for your 05 Montana online with no success.
Any GM Dealer should be able to print out a diagram showing the electronic actuators.
If your van has dual climate controls there are more actuators and specific diagrams for your rig would be greatly beneficial.
I did find this video though, how close it is to yours I am not sure.