I have a 2012 F150 with EcoBoost engine. I only get heat while accelerating, otherwise it blows cold.

Is this a common problem and more importantly, what is likely the issue?

Thanks in advance.

 

Heater coil. Is there antifreeze in you floor?

 

Might check your water level too.

 

Is your engine temperature normal , is your antifreeze good ( not gelling ) and proper laval , engine fan running continuesley thermostat stuck open could be many things

 

I'll guess low coolant too.

 

Likely (and easiest) culprit would be low coolant. Could also be a thermostat, or air in the system.

Start with easy first

 

under acceleration your engine is not making hardly any vaccum, stands to reason your vents are vaccum controled. blend door actuator is probably defective or vaccum booster is leaking.

 

Damn. I was gonna mention that but then second guessed it because I figured they were likely electronically controlled. God snag

 

Did you ever figure this out and get it fixed? What was it? I am having the same issue.

 

Similar issue happened to me. Turned out I had a leaking Y-connnector and was low on coolant. The reason you only get heat while accelerating is due to the configuration of the heater core. If you look at the lines going to the core, they are the highest spot in the coolant system, so bubbles in the system tend to migrate there. They are also parallel with the length of the truck, running to the cab. When you accelerate, it pushes some of the hot coolant towards the heater core, thereby pushing some heat into the cab. When braking or coasting, the coolant runs back out of the core via gravity and the air bubble replaces it, which is why it starts blowing cold air again. A similar thing probably happens on hills. I noticed that I only got heat when going up a hill, and my fans blew cold air on flat ground or going down a hill. This is because gravity was forcing hot coolant into the heat core when going up a hill (i.e. the heater core was lower than the supply lines) and the bubble returned as the truck righted itself or went down a hill.

Apparently the water pump does not provide enough differential pressure to force a small bubble out and into the expansion tank. I ended up being low on coolant, but not my much. I topped off my expansion tank and went for a drive up and down a few big hills to force the bubble out (or just floor it and brake heavy a few times). That solved the heater problem until I was able to fix my leak.