Turned on heat/air this morning while i was driving and it came on but not with full force and i could not control the fan output,also when i would come to a stop(idle) the air out put would drop to almost nothing then when i would accelerate the fan output would raise again but not to full output. turned it off and tried again but this time no output at all. what do I check/replace/repair? thanks so much!
Start by having your charging system and your battery tested.
The heater fan is a DC motor sensitive to changes in voltage. It sounds your voltage is dropping at idle, and maybe not even giving you full output at operating revs. .
You might also have a failing heater fan motor. But my money is on your alternator or battery being bad.
+1 to mountainbike’s diagnosis.
Depending on how old the battery is, it might just be a weak battery, but I think it is more likely to be a failing alternator–which will kill the battery in short order if it is not replaced promptly.
I hope this isn’t still the original battery. If it is, replace it immediately. If the summer heat doesn’t kill it, the winter chill will