The blend door in the HVAC plenum controls temperature, and that door has an electrical actuator that may have failed. Switching door(s) for diverting air to the different outlets is set by vacuum controlled diaphragm(s) and maybe either a diaphragm has failed or you have a vacuum line problem.
Since both are controlled by the HVAC control panel/module you replaced, sounds like even though you replaced it, it may not be working correctly - the only way to diagnose is to check the electrical line to and back from the actuator for correct readings, and vacuum lines at the controller and diaphragm(s) for vacuum. You should also recheck the connections to make sure they are correct..
If you used a replacement controller from another vehicle, the replacement controller must be an exact match to the HVAC option in the vehicle, and a new OEM version is strongly recommended if you can find one. Try YouTube to see what's involved in fixing these components.
SOURCE: 1996 buick roadmaster keeps overheating:
A shotgun approach to repairs can really rack up the bills.
If your symptoms are loss of water and you have replaced the thermostat, you more than likely have an issue with steam. And that steam more than often comes from a bad head gasket. Most head gasket gasket failures seem to be confined to the water side initially, but let it go on bigger damage will occur.
You can buy a litmus test strip to dunk in the coolant. It will indicate if there are exhaust residuals in the water and thus a gasket failure.
However it may just be something simple, given that you have just about replaced everything:
have you given the radiator a good hosing inside and out?
is the radiator fan running when it should be?
SOURCE: heater core replacement
OK, Ifound the problem with mine. Dont unplug your air dryer. I checked the 2 hoses coming out from the heater core and still one was hot and the other not hot. The top one comes from the radiator fill tank and the bottom one comes out of the core and goes around to the front and into the water pump. I disconnected both close to the core and could runwater through both directions so upon further examination, I disconnected the hose at the water pump and no water flow. The hose was plugged up with something. Once I cleared it with a hanger and reconnected it I had water flowing through the core and great heat. Hope this is your problem too as it is aneasy fix
SOURCE: 2000 buick lesabre Heat control will not switch
their is a little motor on your duct work that moves a door open and closed to switch from heat to cool,it is called actuator motor.watch it and have someone to switch it from cool to heat to Se if the motor is turning.
SOURCE: Buick allure 2005 heater blow warm air, have to
The heater radiator had to be flushed twice at the dealership. No problem since then.
SOURCE: My Buick does not throw any heat from the defrost
Either the heater control valve or the vacuum switch.
If you look down under your dash towards the glove box you will see the heater core cover. On top you will see a lever, conected to a rod.
If you pull that as you have your blower fan on you should be able to manually adjust that lever until heat is flowing.
Please let me know.
Air
Temperature Control Blend Door Failure No Heat or no AC (dependes on
where door sticks)
In
all modern cars there is a tiny DC electric motor driven gear drive
that moves a plastic door that blends heated and cooled air from the
AC and the heater core, this is called (interestedly enough) the air
temperature control blend door actuator. The motor that moves this
door fails because the door starts sticking from warping, most common
complaint is no heat but it can be no AC as well. To replace these
parts (blend door and blend door actuator) you must remove the entire
dash from the car. Always have this problem confirmed by a dealer or
qualified repair shop as it is a very expensive repair.
Other causes of no heat in the cabin are engine thermostats that are stuck open (engine runs cold) or air bubbles in the cooling system.
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