99 Sebring conv. with heater problems. On initial start-up, the engine warms up and the temp gauge reads normally. The heater starts blowing warm air and then all of a sudden it starts blowing cold air. I turn off the fan so I don't freeze to death and wait awhile. I turn the fan back on and it is warm again. Any ideas?

 

is this an automatic tempature controlled a/c heater system?

did you check the coolant level?

 

It is not an automatic climate control, just the standard dials for mode, fan, and temp. I did check the coolant level and it is full. Tonight after my wife got home with the car, I drove it around and played with all the controls, turning them to every combination there is and it seems to be working normally now. It continues to blow hot air, but I am not sure if it is really fixed because I didn't actually "fix" anything.

 

I would have to think something is going on with the blend doors. either they're not being able to switch for some mechanical reason or the bcm isn't able to switch it. unfortuantely if its working we can't really find whats wrong with it. Hope it stays fixed.

 

It is most likely a blend door problem. I'm not sure about yours, but some are vacuum controlled and some are electric. Either way it is possible that the airflow (especially at high fan speeds) is actually moving the door instead of the door controlling the airflow. Figure out which and why.

If it's vacuum, a control valve or line may be leaking or kinked, or a diaphragm may be bad.

If it's electric, a linkage control may have come loose allowing movement of the door or the motor, or control for the motor is bad.

 

dcotter0579 gave the following (for a 2001)

Unfortunately, nobody on here seems to know what any of the codes mean. But, it would give you something to ask a dealer mechanic about, assuming that works on your vehicle too.

MRR

 

Me personaly say its low coolant or a clogged heater core but thats just me.

 

I have to agree a flush and refill might do a world of good ,, and if you can back flush the heater core all the better

 

Okay, I have more info for you after this weekend. We were out of town and the car was parked at a hotel Sat. nite. Sunday morning, it was 10 degrees out when I started the car. I let the engine warm up while we stayed inside the hotel. When we came out, the temp gauge was in the normal operating range.....but ZERO heat!!! We drove the car for about a half hour and then like a lightswitch, the heat started and stayed going! Does any of this help? I would think if the heater core was plugged, the heat would be minimal even when working. Can a blend door do this? Just from listening to the car, I thinkmy HVAC controls are vacuum operated.

 

A simple, YES.

Something that may get you by...
Sometimes, if it is a weak vacuum problem, you can try running your fan speed on the lowest setting until the blend door makes it all the way to whichever side you want. (cold or hot) Then try running up the fan speed one notch at a time. You may find this to work until you fix it correctly. (I have the same problem in my Jeep, but it is with the defroster diverter not the blend door.) You'll likely need to keep your temperature selector all the way to one side or the other to keep the door still with the fan blowing. (You'll probably find the door swings to cold on it's own at speed 3 or 4.)

Either that or your clog just unclogged. A radiator flush is routine maintainence and is also advised here.