A/C - Erratic or Insufficient Temperature Control
Article No.99-8-8
05/03/99
CLIMATE CONTROL - ERRATIC OR INSUFFICIENT
TEMPERATURE CONTROL - EATC EQUIPPED
VEHICLES - SERVICE TIP
LIGHT TRUCK:
1995-1999 EXPLORER
1997-1999 MOUNTAINEER
ISSUE
Concerns of erratic or insufficient temperature control, where temperature control does not match setpoint, or where temperature gradually wanders away from setpoint have arisen. These concerns may be caused by various items that are listed in this Service Tip TSB article.
ACTION
Follow Service Tips indicated to aid in normal diagnosis of the Electronic Automatic Temperature Control (EATC) system.
SERVICE TIP
Refer to the following diagnostic procedure according to the symptoms listed if no Diagnostic Trouble Codes (DTCs) are obtained from the EATC self-test, which should be performed prior to any other diagnosis.
Vehicles with "No/Erratic temperature control," or "System works in Auto, but not in Manual mode" symptoms:
Drive actuator in both directions while visually checking actuator for movement.
1. If there is movement, remove actuator and visually che6k blend door where the actuator rod inserts for cracks. The instrument panel does not have to be removed for this operation. If the door is cracked, order a service plenum. Refer to the Service Plenum Tips in this article.
2. If there is no movement, diagnose system according to pinpoint tests in the appropriate Explorer/Mountaineer Workshop Manual.
Vehicles with "System does not maintain setpoint temperature" or "Setpoint is reached but system gradually cools" symptoms:
Inspect the in-car temperature sensor aspirator tube for proper connection at both ends. Also check to make sure the in-car temperature sensor housing is attached to AND FIRMLY seated to the dash panel. The sensor is mounted on two (2) pins. It is possible for the sensor to be attached to the pins but not seated against the dash panel which will cause this symptom.
EATC ASPIRATION TEST
This test will determine if the In-Car Temperature Sensor (ICTS) is receiving enough aspiration. A lack of aspiration can result in an incorrect ICTS reading and cause the automatic temperature control to act erratically with symptoms like: EATC blowing too cold or too warm.
1. Cut a piece of toilet paper or tissue paper about 2.5x2.5 cm (1x1") (paper towel will not work).
2. Turn the key on, turn fan speed to HIGH BLOWER, select PANEL or VENT mode.
3. Place the piece of tissue paper over the aspirator grille opening, if aspiration (suction) is present, the tissue paper should "stick" to aspirator grille.
4. Slowly lower the fan speed to LOW BLOWER. The tissue paper should still "stick" to aspirator grille.
5. Turn fan to HIGH BLOWER, then turn fan OFF. Tissue paper should fall off.
6. If the tissue paper falls off the aspirator grille when the fan is ON:
a. Check that the aspirator hose is properly connected at both ends (at plenum case and ICTS).
b. Check for proper size aspirator hole in heater plenum (19 mm (3/4") 1999 model year only).
c. Check that the ICTS is properly sealed against dash panel with no gaps.
d. Check for kinks and cuts in the aspirator hose.
e. Repair as needed.
Other
^ Check for proper operation of the heater water valve. Visually inspect vacuum hose for kinks, leaks, or disconnects.
^ Temperature differentials between panel and floor vents in mix modes and temperature setpoints that are not at full cool. Setpoints not at full cool or full heat may exist and are a normal concern and not repairable.
SERVICE PLENUM TIPS
This procedure applies to 1995-1999 Explorers when service of the blend door/plenum or actuator is concerned. The following applies to EATC-equipped vehicles:
1. 1998 and 1999 blend door actuators are electronically different than 1995-1997 blend door actuators and cannot be interchanged.
2. The service plenum for 1995-1999 model year vehicles is the 1999 model year Plenum (F87Z-18471-DA).
3. The service plenum may be different from the plenum being removed from the vehicle in the following ways:
a. The service plenum has the blend door actuator mounting bracket molded in the plenum. If you have a new or original actuator with the mounting bracket attached, remove the bracket and discard.
b. The service plenum will have a hole about 19 mm (3/4") diameter near the heater core cover. This hole is the location for the aspirator tube connection on 1999 model year vehicles. If the service plenum is installed on an earlier model, this hole should be plugged.
c. The service plenum has a nylon blend door which is stronger than the ABS plastic door installed on vehicles built through April 1998.
4. When installing actuators on the plenum, there will be pressure on the door if the actuator is driven to full heat or full cold position. This is necessary to seat the door and is not the cause of blend door breakage that occurred on earlier vehicles. Driving the actuator to a midrange position will allow easy installation of the actuator.
PART NUMBER PART NAME
F87Z-18471-DA A/C Plenum
OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: INFORMATION ONLY
OASIS CODES: 208000, 208100, 208200, 208300, 208999