No Heat or Air Conditioning

Hi all. I’m clueless when it comes to cars, so please bear with me.

My ‘99 Cougar hasn’t had heat or air conditioning for a few years. I’ve managed to get by until now, but I’m really not looking forward to winter. I’d like to have this fixed within the month.

I purchased a thermostat and was going to have a friend swap the old one out, but my car does something odd. When the air conditioning or heater is turned on, the engine starts revving. It revs up 1/2 RPM, pauses for a moment, then revs again. It will continue doing this until you turn it to regular fan (not the A/C fan) and cooler air (versus the red lines for heat).

Someone suggested to me that this may be my heater core. But why does it do it with the air conditioning too? Any thoughts? And do I just need some juice for the A/C to work again?

Also, the places around here are keen on charging a diagnostic fee of around $100. What are they doing? I hope it’s more than hooking up that thing that reads service engine lights (mine is on for a squirrely O2 sensor).

Your A/C is trying to work but because it is low on freon it turnes on and off. Making the engine idle go up and down. Try a new thermostat but it might be more than that.

Just wondering if you have found a fix to this problem? My 02 cougar does the same thing!!!!!!!