HVAC System - Control Components: Other Mercury Sable IV

Control Components - Manual Climate Control

The manual climate control system heats or cools the vehicle interior depending on the function selector switch (19B888) position and the temperature selected. The function selector switch position determines heating or cooling and air distribution. The temperature blend control setting determines air temperature.

The manual climate control system components are used to select

1. air inlet source (outside or recirculated)
2. blower motor speed
3. discharge air temperature (temperature blend)
4. discharge air location (defrost, panel, floor)
5. A/C compressor clutch (19D786) operation

Control System Inputs

The climate control assembly has three system controls

Function Selector Switch

The function selector switch combines a vacuum selector valve with two electrical switches to supply battery voltage (B+) to the A/C clutch circuit and the blower motor speed control circuit.

Temperature Control Switch

Temperature selection is accomplished with a potentiometer connected to the electric blend door. Movement of the temperature control switch (19C733) from COOL (blue) to WARM (Red) causes a corresponding movement on the air temperature that the air system will maintain.

Blower Motor Switch

The blower motor switch (19986) controls blower motor speed by adding or by passing resistors in the heater blower motor switch resistor (19A706).

Evaporator Discharge Air Temperature Sensor

The PCM (12A696) determines A/C compressor clutch cycling based on input from the evaporator air discharge temperature sensor (19C734). The evaporator air discharge temperature sensor

1. maintains evaporator core temperature, and prevents icing of the evaporator core (19860) by disengaging the A/C compressor (19703) when the evaporator discharge air temperature falls below a preset level, and engaging the A/C compressor when evaporator discharge air temperature rises above a preset level. For information regarding operating temperature specifications, refer to «REFRIGERANT SYSTEM TESTS»(ref-178710-S12430105252005062100000) .
2. contains a thermistor which receives a reference voltage from the PCM. The thermistor then varies the resistance to the reference voltage based on the evaporator discharge air temperature, and returns the resulting voltage to the PCM. The PCM determines evaporator air discharge temperature based on the return voltage value.
3. is located in the heater core and evaporator core housing just downstream of the evaporator airflow.

Heater Blower Motor Resistor

The heater blower motor resistor (19A 706) has the following features

1. The assembly is located in the passenger compartment on the heater core and evaporator core housing (19850) next to the blower motor assembly (19805).
2. Three resistor elements are mounted on the resistor board to provide four blower motor speeds.
3. Depending on the heater blower motor switch position, series resistance is added or bypassed in the A/C blower motor circuit to decrease or increase A/C blower motor speed.
4. An overheating device (thermal limiter) will open the resistor coil when the temperature reaches 121°C (250°F) interrupting the blower motor operation in all speeds except high.
5. The thermal limiter cannot be reset and is not serviceable

A/C Electronic Blend Door Actuator

The A/C electronic blend door actuator (19E616) is located on the rear of the A/C evaporator housing.

1. Its function is to move the air temperature blend doors on command from the temperature control switch.
2. The A/C electronic 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 the position of the air temperature blend door.

Vacuum Control Motors

The vacuum control motors (18A318)

1. are located on the A/C evaporator housing, A/C recirculating air duct (19C590) and heater air plenum chamber (18471).
2. direct system airflow to the vehicle interior as determined by the function selector switch.

Control Components - Electronic Automatic Temperature Control (EATC)

With the use of a microcontroller, the electronic automatic temperature control (EATC) module (18C612) analyzes input from the following major sources

1. temperature, air distribution and blower selection (made by the vehicle occupants)
2. in-vehicle temperature
3. ambient temperature
4. sunload
5. vehicle speed
6. engine coolant temperature

Using these inputs, the microcontroller determines the correct conditions for the following outputs

1. A/C compressor clutch (19D786) operation
2. blower speed
3. air temperature blend door position
4. plenum/floor door position
5. windshield defroster door position
6. air inlet door position
7. floor console door position.

The PCM (12A696) determines A/C compressor clutch cycling based on input from the evaporator air discharge temperature sensor (19C734). The evaporator air discharge temperature sensor

1. maintains evaporator core temperature, and prevents icing of the evaporator core by disengaging the A/C compressor (19703) when the evaporator discharge air temperature falls below a preset level, and engaging the A/C compressor when evaporator discharge air temperature rises above a preset level. For information regarding operating temperature specifications, refer to «REFRIGERANT SYSTEM TESTS»(ref-178710-S12430105252005062100000) .
2. contains a thermistor which receives a reference voltage from the PCM. The thermistor then varies the resistance to the reference voltage based on the evaporator discharge air temperature, and returns the resulting voltage to the PCM. The PCM determines evaporator air discharge temperature based on the return voltage value.
3. is located in the heater core and evaporator core housing just downstream of the evaporator airflow.

A/C Ambient Air Temperature Sensor

The A/C ambient air temperature sensor (19E702)

1. is located in front of the A/C condenser core (19712) near the center of the vehicle.
2. contains a thermistor which measures the temperature of outside air as a resistance and sends that reading to the electronic automatic temperature control assembly.

In-Car Temperature Sensor

The in-car temperature sensor (19C734) operates in the following manner

1. A thermistor in the in-car temperature sensor measures air temperature inside the passenger compartment.
2. An automatic temperature control sensor hose and elbow (19D888) is connected between the A/C evaporator housing (19850) and the in-car temperature sensor.
3. The automatic temperature control sensor hose and elbow takes air from the A/C evaporator housing air stream to create a suction in the in-car temperature sensor.
4. The suction draws in-vehicle air into the in-car temperature sensor and across the thermistor.

Solar Amplifier (Sunload Sensor)

For additional information on the location and service of the solar amplifier (13A018), refer to Sunload Sensor .

A/C Blower Motor Speed Control

The A/C blower motor speed control (19E624) is located under the A/C evaporator housing, near the blower motor (19805).

1. The function of the A/C blower motor speed control is to convert low power signals from the electronic automatic temperature control module to a high current, variable ground feed for the blower motor.
2. A/C blower motor speed is infinitely variable and is controlled by the electronic automatic temperature control module software.
3. A delay function provides a gradual increase or decrease in blower motor speed under all conditions.

The A/C electronic blend door actuator (19E616) is located on the rear of the A/C evaporator housing.

1. Its function is to move the air temperature blend doors on command from the control assembly.
2. The A/C electronic 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 the position of the air temperature blend door.
3. A 5 volt signal is applied to the ends of the potentiometer. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the electronic automatic temperature control module and is matched with the wiper voltage of the module potentiometer. The control module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the control module wiper voltage.

The vacuum control motors (18A318)

Scheme 146

Scheme 147

1. are located on the A/C evaporator housing, A/C recirculating air duct (19C590) and heater air plenum chamber (18471).
2. direct system airflow to the vehicle interior as determined by the electronic automatic temperature control module or manual override.

Refer to DIAGNOSIS AND TESTING .

Scheme 148

All vehicles

Scheme 149

Scheme 150

Scheme 151

1. Using the special tool, pull out the integrated control panel (18C858). Vehicles with manual climate control
2. Label and disconnect the electrical connectors. Remove the integrated control panel. Vehicles with electronic automatic temperature control (EATC)
3. Label and disconnect the electrical connectors and the in-car temperature sensor hose (19D888). Remove the integrated control panel. All vehicles
4. To install, reverse the removal procedure.

Scheme 152

Scheme 153

Scheme 154

Scheme 155

Scheme 156

Scheme 157

1. Remove the integrated control panel. Refer to «Climate Control Assembly»(ref-178888-S40330094502005062400000) .
2. Remove the right-side lower instrument panel insulator.
3. Open the glove compartment. Pressing the tabs inward, lower the glove compartment towards the floor.
4. Remove the screw.
5. Remove the screw.
6. Disconnect the remote climate control (RCC) module electrical connector.
7. Remove the two nuts. Disconnect the plenum vacuum harness. Remove the RCC module (18C612).
8. To install, reverse the removal procedure.

Scheme 158

Scheme 159

1. Remove the integrated control panel (18C858). Refer to «Climate Control Assembly»(ref-178888-S40330094502005062400000) .
2. Remove the knob (18519).
3. Remove the screw. Rotating the blower motor switch counterclockwise, remove the blower motor switch (19986).
4. To install, reverse the removal procedure.

Scheme 160

Scheme 161

1. Remove the integrated control panel (18C858). Refer to «Climate Control Assembly»(ref-178888-S40330094502005062400000) .
2. Remove the knob (18519).
3. Remove the screw. Rotating the temperature control switch clockwise, remove the temperature control switch (19C733).
4. To install, reverse the removal procedure.

Scheme 162

Scheme 163

1. Remove the integrated control panel (18C858). Refer to «Climate Control Assembly»(ref-178888-S40330094502005062400000) .
2. Remove the knob (18519).
3. Disengage the retaining tabs. Remove the function selector switch (19B888).
4. To install, reverse the removal procedure.

Scheme 164

Scheme 165

Scheme 166

1. Remove the four scrivets and the grille.
2. Detach the ambient air temperature sensor (12A647).
3. Disconnect the ambient air temperature sensor.
4. To install, reverse the removal procedure.

Scheme 167

1. Remove the integrated control panel (18C858). Refer to «Climate Control Assembly»(ref-178888-S40330094502005062400000) .
2. While pressing the retaining tabs inward, remove the in-car temperature sensor (19C734).
3. To install, reverse the removal procedure.