How do I go about diagnosting my A/C? Specifically, my heater is not working and my front shield defroster is not working. No air is going to the front side and its just plain air. Neither cold nor hot. Any ideas?

 

Look in the FAQ section for the link to the 89-91 Factory Service Manual (FSM). There is an extensive section there for troubleshooting the heat & a/c system. Start at the top and work your way down.

If air is not coming out of the appropriate vents during some modes of operation, you should focus on troubleshooting the logicon (notorious for bad solder joints, and there are people on this forum who refurbish them), and the little servomotors that move the dampers in the heater section. The one on the left controls the water valve that lets hot water into the heat exchanger, and the one on the right side of the box controls the dampers that direct the air to the various vents. The motors can burn out, the logicon may not be commanding them, and sometimes the little pushrods just fall out of their connectors and need to be reattached.

Apparently your blower is working... that's good news.

That the air is neither cold nor hot suggests the motor on the left side is not operating, thus not moving the hot water valve. That air is not coming out of the appropriate vents suggests the motor on the right side is not working, or not working correctly. It is unlikely that both motors failed at the same time, so I think there is a high liklihood that your problem is in the logicon. There is a bench test process in the FSM such that you can put power on the box, and check voltages at the various outputs and see where the problem is--or eliminate the logicon as the source of the difficulty.

 

Thanks calpatriot. Its good to be back here. Quick and reliable answers. I'll check the FSM first and will report back my status. Thanks.