Temp gauge and A/C problem

[EdP]

Would the AC Compressor effect the thermostat and cause it to stay at C?

Not enough information. The temperature starts on C but as the engine warms it goes up. Does it go back to C at low RPM?

 

[Gunkk]

Could it be a bad temp censor? In this forum, I was reading that the cpu could be shutting off the ac to keep the car from overheating since the cpu does not know the car true engine temperature

That's possible. If the temp dash gauge is varying rapidly between all the way cold and normal and back, then yes there might be something amiss in that sensor circuit, including the sensor.

A wildly fluctuating engine coolant temperature reading (normal to hot back to normal again) is most often caused by excessive air in the engine coolant loop. Can be a sticky thermostat, but isn't usually (they usually either work or don't work). Bleed the engine/radiator coolant loop as appropriate.

HVAC Blowing hot air at idle but cold when moving, then blowing hot while idle again is typically due to condenser/cooling fan issues. If the fans don't kick on at idle with the AC running, troubleshoot there. Blowing hot at idle after the car sits in the summer sun is normal until the car starts moving and cabin air cools down.

Reading through the 2012 4.6 HVAC service manual I came across the diagnostic below. F.A.T.C stands for "Full Automatic Temperature Control." I have not tried this diagnostic on my car, but it may be able to provide some insight.

 

[GenXesis]

I know this is an old thread but I wanted to share my recent experience that was similar.

While driving two days ago, the AC started blowing hot, the engine light came on and the temp gauge bottomed out at "C".

The error code was:
P0116 [0x0116]
Engine coolant temperature (ECT) sensor - range/performance problem
Status: Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle.

Upon inspection, there was no coolant in the reservoir. Prior to this, I never received any warning, smelled a burning engine or had any reason to believe there was an issue.

I filled that up, topped off the radiator itself with the remaining (about 2/3rds) jug, so it was low as well. I cleared the code and cycled it 5 times yesterday with various errands. I ran the OBD dashboard while driving is and coolant never exceeded 192*. The AC was cold during each drive.

I cleaned the engine and bottom splash guard with degreaser and will continue to monitor the reservoir and radiator daily checking for leaks but I think it threw the code due to low coolant.