In my opinion, as I've had the same thing happen, is that your heater control valve is not closing all the way.

If you clamp off the hose behind the kick panel on the passenger side, the heat will no longer come out.

This gives you time to source the valve and install it when it is convenient for you.

By doing this, your A/C won't be fighting the heater core and the cabin will be coll.

Hope this helps.

Matt

Hi,
I’ll assume air flow is equal from the fan, it’s just temperatures are off?

Yes, you are correct that air from outside gets heated by the core but also there are return air ducts beneath the seat. They bring air from the rear seat area.

It is possible that a vacuum motor, on one side or the other, is not operating properly.

When your central control button is in the “recirculate mode” a main door closes behind the heater core. It closes off outside air from the outside cowling vent.

I believe, in this mode the lower return air ducts are opened to bring more air accessibility to the fan plenum.
Think of it as, another air intake port to supplement the amount lost from the outside.
This air will always be cooler air than the rest of the cabin because it is down low on the floor. Hot air always rises.

I’m not totally sure that the recirculating mode is allowed to cut off all air completely, as there should be up to 20%, makeup of fresh air induced.
That is what it’s supposed to be for commercial building anyway.
The Automotive industry may not be bound by the same rules.
One is the heater must fail in heat mode if it’s not controlled manually!
Say if, by a vacuum system, if no vacuum, the valve must fail open! Vacuum holds it closed.
This could save your life in a blizzard.
In the desert, you will get only uncomfortable as **** can be!

So with that said, a vacuum motor must fail in one direction or the other for safety reason.
You may have this situation where one is bringing you colder air, when the other side is not.

Same goes for the other vents, but don’t ask which way they are designed to fail. In actually, (-:)
To fail open, is to not restrict and that would be my first thought in your case!

Just peek around, on each side of the console, by removing the side panels and see if one is opposite of the other one in recirculated mode.
Heating or cooling should not affect their operation, but only the three button selector switch.

Hope this helps.
I have not had to dive into that system, for repairs below, so it is an unknown territory and complaint
to me?

In more thinking, you might check for a child’s socks in one of the return air vents, under the seats.
If you open the side panels look around for excessive dog hair or alike to be in behind the heater core.
To be only on one side might sound tricky, but that depends on which side a dog can lie around some railroad tracks too! (-:) | | (:-)

Phil