Kiantone

'89 Coupe with electronic heater AC controls. When I bought the car the heater hoses were off the core and connected to each other by a plastic elbow
as the core leaked. I had a trusted shop install a new core and it had plenty of BTUs. I should of had them look at the blend door while in the shop as the heat was controlled only by the speed of fan. Until today, no heat at all, engine temp 188, warm heater hoses, heater fan runs, no spots of leakage on the floor. I wish now I had flushed the system but I would not think the new core would plug that quickly. The car sat about two weeks from lots of heat until today. What am I missing?

hooked073

I wuld say the chances of that are low. I would check blend air door like you talked about. Also make sure you are full of cooleant

Kiantone

The plastic tank had plenty of fluid in it. So the blend door had one last move in it? It is designed to cycle at every start up? I have read about them but will need to reread before I can claim an understanding. Is there a way to push it back to allow some heat to pass?

Cliff Harris

The blend door position is calibrated at every key-on. It goes to full cold, full hot and then to the position set on the HVAC control head. All this takes about 15 seconds.

You can remove the blower motor controller from the top of the evaporator housing to see the position of the blend door. This picture shows it in the 90°F position:



If the blend door motor only goes in one direction and then stays there, then the HVAC programmer probably has a problem. It is located above the gas pedal. It is very common for the two large resistors to either burn up or get hot enough to crystalize the solder and cause a bad connection. Here's a pic, showing the discoloration around the resistors (lower left corner):



The blend door motor has a gear train with a VERY large reduction. It is not possible to move the blend door by hand (without breaking something). One thing you CAN do is to disconnect the rod that controls the blend door position and then wedge it somehow so it stays in the hot position. The rod is held by the white plastic piece on the end of the motor arm and you can pop the rod out of the plastic part. Here's a pic from the top to give you an idea of what to look for:

Kiantone

Thanks Cliff and hooked, I think you have tried to help me before. If the resistors are discolored does that mean replace the entire programmer? Cliff could you tell me what you removed to take the last picture? Or where is the view from?

SunCr

Blend Door position is only calculated when power has been removed so disconnecting and reconnecting the battery - or removing the fuse - should make that happen. Otherwise, inputs are from the Inside and Outside Temp Sensors which is why you can get A/C on Auto on a 50 degree day if the Sun has cooked the Interior up to a 100 degrees. What you might sense as a brief delay that occurs when you start this year is to purge moisture from the vents by blowing a small amount of air through the heater - that keeps the windshield from fogging up. Anyway, if you want to see what or if the Blend Door can move, remove the Blower Module from the Evaporator Case and look inside. Then disconnect and reconnect the Battery. Turn the key on and you should see the Door being cycled (helps to have an assistant). The temp readout will be something like -38 and nothing - Blower Motor; a/c compressor or any of the HVAC Controls will work while the door is being cycled or this learning period is taking place. After a couple of minutes, the process will end and everything will/should work. If the door didn't move, it's probably because the plastic link that connects it to the motor that moves it has broken - particularly if someone got careless with it replacing the Core - or crap, they can just break when you try to disconnect it after 20 plus years. All of that is on the inside - passenger side - remove the hush panel to access. You can confirm by getting on your back and removing/reconnecting power (again) and listening/feeling for a running motor.

As to your new core clogging up - yes they can; particularly on the '89 which can make copious amounts of crappy, sludgy stuff if the head gasket is weeping exhaust into the coolant. That's another, but unfortunate common issue with this year and the process can occur within months of a coolant change.

Cliff Harris

The resistors WILL be discolored. The question is how bad are they? I have heard of resistors that got so hot they broke into pieces. The most common thing that happens is that the solder crystalizes (gets rough and looks dull). When that happens you usually get a bad connection. The cure is to put some fresh solder on the connections. If the resistors are really bad they can be replaced. The original resistors are 140 ohms 1W 5%. I recommend replacing with 2 watt resistors -- more resistant to the heat.

The picture was taken from the top with the dash pad removed. The passenger side dash air duct was also removed. Agent 86 once upon a time posted a picture from the bottom. Let's steal it: