It's a chilly, wet day in my neck of the woods today, so I used the defrost setting with max heat to defog the windshield of my '79 Catalina. I noticed when I put the car in park at the gas station that the engine was on the fast idle again. It came off when I put the selector on Heat only. Is that normal? I assume the defrost setting attempts to run the air conditioner like a modern car and it's compensating for the added load.
As far as I know, the A/C does not work in the car, will it trying to run when the selector is on defrost cause damage to the compressor? I wouldn't expect these ancient systems to have the special sensors that modern cars have to protect the system.
When the defroster is activated, it automatically activates the air conditioning whether it works or not. This is to dry the air.
That's what I thought. Thanks. Wasn't sure if the old technology would stop that from happening if the system isn't working.
No, it's not that sophisticated. It bumps up the idle whether the compressor is working or not. On some older cars with AC the manufacturer just specifies a higher normal idle and calls it a day. (My '71 Ambassador is like that.)