Q: My 04 Mercury Mountaineer SUV is blowing hot AC in the second and third row upon start up whenever it feels like it. It does not happen all of the time and never happens when I want to show the service dept at the dealer what it is doing. It does not switch to hot once it has been blowing cold, it only is at start up that it blows the hot and usually when the fan blower is on full power. I have had it to the dealership 4 times, and they have changed a bunch of parts, but still can not solve the problem. Their solution is to bring it in when it happens and not to touch anything. This is not possible since I have my young kids under that full power heat blast and I live in Arizona! Both AC knobs in front and rear are set to cold ac when this happens and cycling the front fan speed knob about 5 times makes it blow cold again. It is not throwing any codes. What could be causing this???
A: My guess is either one of three things.... (there are more possibles but here is my thinking) The a/c charge isn't to the correct factory level... (there have been buletins about some lines being undercharged at the plant and to correct vehicle labels due to it. The a/c valve (called an expansion valve) that limits flow of freon into the rear a/c is messing up and getting stuck at times and causing your concern The a/c blend door or it's motor is bad and causing the heat instead of cool... My guess is number 2 however...