Heater problem, not very hot & not switching from defrost to floor

In the attached drawing, Part 32 moves Part 26 to direct the air flow to the desired locations. It uses vacuum to operate. The actuator may be bad or the vacuum hose my have come loose when the heater core was changed. With the car running but the blower off stick your head up under the dash on the passenger side and see if you hear a hissing sound. If so it's probably just a vacuum hose come off.
AIR CONDITIONING AND HEATER UNIT BODY Fits DYNASTY LASER LEBARON NEW...

Common failure the mode door motor is broken there are 2 mode door motors on the passenger side 1 for fresh / recir. air and the other position of heat/cold on drivers side has 2 also blend air and defrost/ floor . these are fun to remove usually held in with 2 5.5mm screws.

heater control could be faulty or vaccum to control unit is not sufficient or possible air duct abstruction not letting switch from floor to defrost.

the dampers are failing.
first check fuses.... as always.....
ok some cars have cable dampers others use elect. motor dampers
the FSM covers the tests, on this. electric is hardest.
if cable drive, just look are they working>? simple it is.
the cable most move on both ends, is it? and still connected>?

I assume your heater setting is electric control, if so either your defrost and floor heat switch failed or wire problem. For the air not hot, check the heat control valve on the top of the hose it should be in front of the firewall. I don't know your car is using mechanic valve or electric control valve. Anyway check there first. Good luck.

defrost is the defalt mode look for a damaged vacuum line going ti the control head

is the climate control switching over like from floor to defrost to vent ? maybe the flap door not working in heater box.both hoses are hot but is water flowing thru heater core.

When the engine is cold,check the coolant level.

Make sure it's on max.

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A coolant system should be flush every two years.

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If you did a coolant flush recently then air pocket can be the cause of the un-even heating problem.

The DIY method is to drive you car onto a ramp or a steep hill.

Iet the engine cool off and top off the coolant tank.

Set MAX heat + MAX fan

Let the engine ran for 20 minutes wih the cap off and the trap air will escape from the coolant reserve tank,

Check coolant level and top off coolant when the engine cools down.



A shop will charge $75+ for this but using an air operated excavate tool!

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A car with over 90K miles may experience linkage problem to the heater control valve.

The heater control valve (near the firewall) may be stick over time.

Open the hood and move the heater to max and min. Back and forth.

Clean and lube the linkage with WD-40 to free the heater control valve.

If it's a vacuum type heater control valve then cash for leaky vac. hoses.


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Move the fan switch back and forth to re-new the electrical conductors.

Pass a vacuum over the control panel to prevent dust build up behind the console.

Defrost is the default mode so if the system fais, you alays have defrost. The mode doors are controlled by vacuum motors. I would suspect a vacuum leak in the engine compartment on the hose going from the engine through the firewall and into the heater controls. Some systems have a vacuum storage canister that can also leak. The canister stores vacuum when vacuum drops going up a hill.
Or, you have a bad heater control head that is not passing vacuum to the vacuum motors on the mode doors.

Here's a diagram of the system for reference.

First check to see if the water to the heater core is hot. if not then you need ti check the hot cold vale . it is an electric valve that opens to let the hot water bvy.