1999 Mercury Marquis

Heater problem
1999 Mercury Marquis V8 Two Wheel Drive Automatic 135000 miles

Just recently all I would get out of the defrost and floor vents is cold air. The blower motor speed works fine, So I found the vacume lines under the dash(behind the cup holder) and disconnected the yellow line to the diafram and bingo now I have heat. The problem is that I can't controll defrost or floor selection or hot and cold settings. When I run the EATC test it don't show any codes. What do I check next? Or what need to be replaced? Thanks.
Greg Becker
October 4, 2009.

Plug that yellow line and see if you get back control of desired airflow? It sounds like your temperate blend door actuator is bad or the shaft on that door is stuck, these can rust and then get hung up. If airflow stays on defrost, or goes to defrost while driving under load(low manifold vac) your reserve tank is cracked, or the supply line/check valve is broken someplace, usually this is a black line, but Ford does use white too! This line comes in from the engine to the control head. Here's the diagnostic test, just in case your had bad info on how to do it.
Run the self diagnostic test on it by turning the key to on, then press off and floor at the same time, then within 2 secs, press auto, If there is a problem a trouble code will appear on the display...To exit self test, press the BLUE, cooler button this also retains error codes, To erase codes and exit, press defrost, choose one of these before you power down the system... Test with engine at 120 degrees or more, and cabin between 40-90 degrees.Post any codes recorded here and I let you know what's defective...

NV=No Vacuum
Electronic Blend Door Actuator The electronic blend door (temperature blend door) is operated by a reversible electric motor (actuator) and potentiometer, in response to input signals from EATC module. The actuator is located on top of evaporator core housing. Temperature blend door actuator contains a reversible electric motor and a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate temperature blend door position. Vacuum Actuators Three vacuum actuators control movement of air distribution doors. The floor/panel door actuator and panel/defrost door actuator are mounted on the heater air plenum chamber. The fresh/recirculated air door actuator is located in the air duct and controls the fresh/recirculated air door.

Oct 4, 2009.
Thanks for the info guys a very strange thing happened today coming home from work and I don't know if its related. I'm on the freeway driving about 70 mph and I look down at the digital dash, radio, clock, heater controls and everything is black can't read nothing. It looked like the car was turned off. After 15 or so miles everything turned back on except the heater controls. This happened several times within 20 miles. And when I got off the freeway and stopped, on came the heater controls. But as I pulled away from the stop sign the heater went off and the battery light came on. When I got home I poped the hood and the battery had black on the top (Blue top Optima 950) and was very hot. As was the alternator. I checked the amp draw and my inductive meter read 108 amps comming from the alternator to the battery at idle? Am I over charging? Also while driving with no dash power I went to roll windows up (power windows) and the radio could be heard as I pressed the window switch. The 12 volt battery is now junk it has only 5.4 volts the next day. Any help is appreciated.

Greg Becker
Oct 6, 2009.
Sounds like a ground problem or loose connectors, you might need to pull out the gauges and check the back of the cluster for loose connectors, or bent or pushed out pins in the connectors. Same with the eatc. If they seem OK, Ignition switch might be the culprit.

Oct 7, 2009.