Ok so I have never had any car I have owned do this but maybe its normal in the Rangers. I went camping this weekend and like a dumb *** left my sleeping bag at home so I slept in the cab of my truck and when it got to cold to deal with I started my truck and when i turned on the heater the RPMs started to spike! I dont know if it always did this because I dont run my heater a lot and I have never had this happen. Its almost like the ac compressor turned on ! Is this normal or what could cause it?

 

Yes, I believe the AC compressor will run with the mode selector control in any position except in vent and floor position regardless of the temperature settings.