94 Roadmaster climate control issue

[Bohb]

The heat output of my 94 Roadmaster has dropped off dramatically in the last few weeks. Here is what I know.
1. Blower works normally
2. Coolant temp raises normally and runs in the normal, mid scale, range (about 195 F).
3. Coolant level is correct and has not changed in last month as far as I know. I did have an oil change last week and they might have topped off the coolant but there is no indication of that on the receipt
4. Air comes out of the correct outlet based on where the control tells it to go.
5. This morning I drove fast on a bumpy road and it started putting out heat but the next time I started the car it blew cold again, even set at 90 degrees.
6. Cycling the temp from 60 to 90 multiple times makes no difference
7. It doesn't matter whether it is in Auto or Vent mode.
8. The AC works normally
Questions
1. Are the actuators vacuum or electrically operated?
2. Are there any other tests I can run to identify the culprit?

 

[silverfox103]

Have you flushed your car's heater core? If you haven't, I think you need to do that.

Tom C.

 

[Bohb]

Thanks Tom. I've just been reading a thread on that procedure. Tomorrow's project. I'll report the results.

Bob

 

[Bohb]

I back flushed the heater core and like the man said, it's fixed. Thanks for the guidance.
Bob

 

[silverfox103]

Glad you got it fixed Bob.

Tom