2007 - Thermostat Acting Up?

[DavisC27]

The problem isn't urgent, just annoying. I'm not even sure if anything is broken at all.

The 2007 Grand Marquis has a temperature controlled thermostat rather than the standard "either hot or cold" heat/AC that most cars have. It's really quite luxurious and I love it.

However, this spring when things have started getting warmer outside but not yet hot, I've noticed the thermostat seems to be getting confused. I'll have it set to 70°, and it'll go from blowing cold air to SUPER hot air, and then about 30 seconds later switch back to cold air again and keep going back and forth. I've owned this car for 3-4 years and can't recall this happening before. Even setting it to straight AC it still keeps going back and forth between cold and hot air every few seconds or so. I got so annoyed today with the hot air blasting in my face that I just turned it off altogether.

My guess is that the thermostat is wearing out and getting confused since the car is over 10 years old. I talked to AutoZone today and the part is super cheap, but they also said there could be another underlying problem with any one part of the heating/cooling system.

Any ideas on how I can diagnose it?

[Stealthee]

Cars with auto climate control are weird. They actually control the temperature based on the outside temperature sensor. If it is 60* outside, but a cool 60*, and you want heat the climate control may think you really don't want heat since it isn't much of a difference in outside temp and requested temp, so it will blow cool air.

[DavisC27]

Sorry for the late response. After further testing I have determined that something is definitely wrong.

It's been around 80° the past few days with my thermostat set to 68°, and my car is still blowing scaldingly hot air when it absolutely should be blowing straight AC at this point. The periods also seem to be lasting longer. I can hear a shift when it changes from hot to cold air, so I believe whatever controls the change from hot to cold is severely malfunctioning.

It's definitely not the radiator cutting off the AC since my temperature gauge is perfectly fine.

I doubt it's related, but I'm due for an oil change and my check engine light came on for a time with the error that the ignition coils and/or spark plugs were misfiring. The light went away but I'm still scheduled for service on Tuesday.