2007 Compass - Heat Only During Acceleration

Recent Repairs:

  • New heater core
  • New radiator cap
  • Complete coolant flush
  • New thermostat housing and thermostats
  • New coolant temp sensor

In the past few days, at idle and the coolant temp where it should be, my heat has gone from warm to cool.

  • Heater core inlet and outlet pipes are hot
  • Coolant temp is fine
  • Engine is not overheating which makes me rule out bad water pump (water pump is only a year old anyway)
  • Not leaking coolant - checked reservoir and it remains the same
  • Air gets warmer as engine revs

The only thing I can think of now is a blend door… does anyone have any experience with the blend doors on this vehicle? Or how to troubleshoot them? Would a bad blend door cause my symptoms?

Two things come to mind.

#1 - air in line. Park car with front higher then rear. When engine is cool remove the radiator cap. Let it sit for a couple hours.

#2 - Weak water pump.

1 Like

This sounds like a classic case of air still in the system

I thought air too… I have bled this system time and time again. My driveway is inclined, so I park the Jeep with the nose in the air, radiator cap off, coolant drain funnel attached, and let it run for 30 minutes.

Should I be doing this with the engine cold? I’ve never heard of that method. I’ve always let the engine run to push out any air, then secure the cap back on the radiator to prevent further air from entering the system. Do I have this wrong?

Even if it was air in the system, why would the heater core hoses be hot? I am getting hot coolant to the core. And I know it’s not clogged because the outlet hose is hot as well. So one would conclude from that, that hot coolant is inside the core while the fan is blowing over it… however - no hot air.

I don’t know anything about the blend door on this specific vehicle, but it sounds like you’re looking in the right direction.

1 Like

Strange turn of events…came out to my car for lunch and the heat works fine at idle. So yay… Now this is an intermittent problem.

Blend doors sometimes stick then unstick. On my Chrysler with auto climate control, the blend doors need calibration periodically. It can be calibrated manually, but it also automatically calibrates every so many key cycles. You could try turning it from cold to hot, wait 10 seconds then back to cold. Repeat a few times. But again, I don’t know what system you have.

Definitely don’t have a system that auto calibrates! Not in this 2007 base model Compass. But thanks for the info.

A blend door problem still doesn’t explain why I am getting heat during acceleration. I’m almost certain these actuators are not vacuum…