Heater stopped putting out heat, blower works fine air conditioning works fine

There are several possible reasons why your blower, vent, defrost, AC, and heater might stop blowing air:

1. Blower Motor Failure: The blower motor is responsible for blowing the air through the vents. If the blower motor fails, you will not get any airflow from the vents.
2. Blower Motor Resistor Failure: The blower motor resistor controls the speed of the blower motor. If the resistor fails, the blower motor may stop working or only work at one speed.
3. Fuse or Relay Failure: A blown fuse or faulty relay in the blower motor circuit can prevent the blower motor from working.
4. Control Module Failure: The HVAC (heating, ventilation, and air conditioning) control module is responsible for controlling the blower motor and other components. If the control module fails, it can prevent the blower motor from working.
5. Vacuum Leak: If your vehicle uses a vacuum system to control the vents, a vacuum leak can prevent the system from working properly.
6. Broken Blend Door: The blend door controls the direction of the airflow. If the blend door breaks or gets stuck, the air may not flow through the correct vents.
7. Wiring or Connector Issues: Faulty wiring or connectors in the blower motor circuit can prevent the blower motor from working.

the ac and heat are two seperate units, the heater hoses are coming from the heater may be loose or cracked check your fuses and relay switches

I woild be checking the vent controls as if the ac is working and the core was blocked then the air would be cool when the heat was selected but not changing Fixing the heater has resulted in a /c not being good enough to cool the air if the vent is not properly selecting. The point is that if the vent selection is not working properly (vacuum hoses) then the 2 faults will be related.

You have pulled loose a vacuum line somewhere during the install.. its "defaulting" to heating mode.

mcdevito75 here, either your son in law didn"t put in enough freon or the compressor is not working, Have your local shop check it out.

sounds as if you have an air lock on your heater try bleeding it or check your heater cable it may be jamed or needs ajustment

Replace power module. Its under the hood. In the air duct up against the firewalll. About 12" to the left of the blower motor. Has 2 connectors on top. Its black. May be hard to notice. Probably have to remove cross brace to get at.it. Then remove 3 screws and pull it out. Put in new one. Reattach brace

open glove box and make sure that none of the papers from that can get down to blower motor

Notes Electronic Automatic (RPO C68)/ Dual Zone Air Conditioning (RPO CJ2)

9 times out of 10 on this old of vehicle its the heater core. If your car temp gauge is working and the car is heating up fine and the blower works then it is most likely your heater core. Not sure how hard it is on that car. SOme times it just under the dash takes about 30 mins but some cars you have to pull the dash out. The part alone is cheap. I would try logging onto autozone.com put in your car find the part (heater core) then look at the how to change section of auto zone.

Goodluck.