No heat?

Only way to find out is feel the heater core hoses.

cold or warm heater core hoses possible plugged core, air in lines or bad heater control valve if equipped.

This guide can help us fix it

https://www.2carpros.com/articles/car-heater-not-working

if theres a difference in temps between hoses could be a bad/plugged heater core, air in lines or plugged lines.

if both hoses are hot its in the dash.

With the engine at full operating temp, locate the 2 heater hoses where they go into the firewall and feel them to see if they are both hot to the touch. If they are.

The temperature is controlled by the use of an air mix door that is operated by an electric motor/actuator. This door can be jammed or the actuator can be inoperative or have stripped plastic gears internally.

Hi:
First, is the engine warming to a normal operating temp? Second, with the engine running, hot, and the heat on, feel both heater core hoses. They should both be hot. Finally, is the coolant level full?

Let me know what you find. IF these things are all ok, we will need to look at the blender door.

Joe

Take it back to the people that fixed the heater core or you can do this yourself. Check to see why mode door isn't getting vacuum as it may be disconnected or a hole in line from heater core replacement.

First do soem stuff yourself, see if both hoses leading to heater are hot it could be no vacuum to water valve on engine. Check for a vacuum leak and check to see if vacuum motors on heater are getting vacuum or are working if they are. Then you need to go from there. Pic enclosed on lh side.

It sounds like the blend door is stuck. It is what determines if you get AC or heat. It is under the dash and half of the dash needs to be removed to access it. That is my first guess based on your discription.

Let me know what you find.
Joe

Do the heater hoses get hot? Does the engine reach normal operating temp? Another possibility is an actuator under the dash.

Just to add, if both heater hoses are hot, I don't think it is the heater core. You could flush the heater core if you wanted?

When your blower motor was working in only one speed "High". It is very possible your blower motor resistor is either stuck or needs replacement.
If you can repair it yourself that will save you some money. Here is what you need to do.

Remove the speed control servo.
Disconnect the electrical connector.(1)
Remove the bolt. (2)
Position the speed control servo (3) aside.

Remove the coolant/washer reservoir.
Remove the two screws and the two nuts. (1)
Move the coolant/washer reservoir (2) aside.

Refer to the sketch below for the blower motor resistor location.
You will see the blower motor resistor (1) just below the vent hose. The arrow is pointing at the blower motor housing.

Turn the heater fan speed selector on "High".
Turn the ignition "On" but do not start the engine.
Get a long screwdriver or something similar and place it against the resistor housing.
Give the resistor a slight tap, listen to see if the blower motor is working. If it isn't, give it another tap.If it is not working, give it one final tap.

If the blower motor is still not working the resistor needs to be replaced.

To remove the resistor:
Disconnect the electrical connector from the resistor.
Remove the two small bolts.
Remove the resistor and replace it with a good one.

You can buy the resistor "new" at an automotive parts store or if you have a "Junk Yard" or "Auto Salvage Yard" near you, you can pick a used resistor up from them and save some money

I hope that helped you out;
Rick

Hi rjmillsbjkl ;
The problem "possibly could" be in that black box.

The resistor is usually always the case 9:1.
There just might be "very slight" chance of (1 out of 9) you did pull a bad relay out at the junk yard.

You mentioned that you grabbed a three knob control so you "do" have the correct resistor that goes with that configuration.
Some mountaineers have a digital "EATC" (Electronic Automatic Temperature Control) and the resistors electrical connector is a little different than the knob type.

I'm thinking the electrical connector may be giving you a problem but not sure... The (resistor you took out of the junk yard)... is it identical to the one you replaced ?
It is now narrowed down to the resistor/ wiring harness/ black box. We have not ruled out the blower motor completely but we should throw that in too just in case.

Just giggle electrical connector (2) in the sketch above and see what happens.... I will be back later on today.

Rick