1991 SDV heater issues

[okccadman]

The heat in my 91 SDV is very testy.  When the air does start blowing warm, it does it for a whilethen fluctuates back and forth hot/cold hot/cold.  Anyine else had similar issues?

[TJ Hopland]

Checked the coolant level lately?   If it was not a fancy auto system I would say for sure its low coolant or air in the cooling system.  With the auto system there could be control issues but might as well start with the basics.

[okccadman]

Coolant is full, thermostat is good and radiator flow well.  im thinking the control unit or some kind of blend door or module

[CEC #20099]

I have a 90 SDV that has had many heater problems. I would suggest you remove the glove box from the dash. On the left, you will see the damper rod & linear servomotor that controls the blend air door.  With the car running & warmed up, you should see the Servomotor respond, as you reset the interior temp higher & lower. There is a removeable link in the rod, that will permit you to manually position the door, without forcing the servomotor.

Evaluate your results. A shop manual is a necessity to diagnose these systems.

I have had severe problems with the evaparator plugging from airborn dirt, & restricting the airflow. It is real fun to clean the exterior.
I have also heard that heater core plugging is an issue.

You can digitally interrogate the coolant temp sensor, via the digital dash diagnostics, to get a CENTIGRADE coolant temp reading, while running.
This diagnosis should give you data to further locate the problem.
c.chleboun # 20099