2000 Mercury Mountaineer Heater Issues...

[Rhubarb]

Hello All,

I am having a issue with my Mountaineer with auto electronic temp control...

It seems to me that everything works fine...heater hoses are both warm, I can hear the blend door working, the fan works fine and dandy on all speeds, the blowing air moves from the defrost vents, to vent to floor and etc... until you have been driving for two hours....

Then nothing comes out of the vents... I can hear the fan blowing, but nothing comes out of any of the vents.

I suspect that it's probably the blend door issue that has been written about all over this forum, but my symptoms don't seem to match up with others I've read about.

I did the self diagnosis test that I read about here on this site...no faults.

After everything cools down, it works fine again until you drive for two hours.

I've had the same thing happen to me in the summer time with the A/C.

Any ideas?????

[shorod]

The blend door won't cause the airflow to completely stop, it should just effect the temperature of the air coming out the vents. Have you checked all vents to see if maybe it's coming out the flow or the defrost vents when it seems to stop? Are you absolutely sure the blower motor is still running? Are you on full auto or manual when this happens? Have you tried switching to the other to see what impact it has? How about changing the set temperature to a higher setting?

The automatic climate control system attempts to maintain a set temperature in the cabin. After two hours of driving I would expect the cabin is pretty much to its set temperature at which time, if in the Auto mode, the blower speed would reduce and eventually shut off the blower motor.

-Rod

[Rhubarb]

Originally Posted by shorod

The blend door won't cause the airflow to completely stop, it should just effect the temperature of the air coming out the vents. Have you checked all vents to see if maybe it's coming out the flow or the defrost vents when it seems to stop? Are you absolutely sure the blower motor is still running? Are you on full auto or manual when this happens? Have you tried switching to the other to see what impact it has? How about changing the set temperature to a higher setting?

The automatic climate control system attempts to maintain a set temperature in the cabin. After two hours of driving I would expect the cabin is pretty much to its set temperature at which time, if in the Auto mode, the blower speed would reduce and eventually shut off the blower motor.

-Rod

I never really use Auto mode, mostly just use manual defrost, floor and floor-def. I can hear the motor blowing at all different speeds (Especially in high...it's pretty loud.) but nothing comes out of any of the vents at any of the settings or temperatures. After it stops pushing out air, I've tried it on every setting and combination of temp/setting/fan speed that I can imagine, including auto.


This doesn't effect the rear vents at all...they still function normally.

Thanks for the quick response Rod!

[Rhubarb]

So...an update, after pressure testing the cooling system, I found that the heater control valve had a slight leak. So I replaced that...21 bucks from NAPA....I took it for a two hour drive and low and behold, the HVAC system acted normally. I don't really know how this could cause the problem above...but we'll see.

I also wonder if maybe perhaps the HAVAC fault scan I did perhaps reset something?

[shorod]

Yeah, the control valve would not cause no air to come out the vents. It could cause the air from the vents to not be hot, but wouldn't restrict the airflow.

The process of checking the DATC for codes does reset all of the servos, but I'm struggling to see how that would be the issue either. In looking at the diagram from the Factory Service Manual showing the airflow, there is no door/servo that can prevent the air from the blower from coming out the vents. About the only things that could prevent air flow would be a restriction in the air inlet (either outside air or recirculating) or if there was something that plugged the fins of the evaporator core or the heater core. And the heater core would only be an issue when the blend door is directing all air through the heater core.

-Rod