Automatic A/c-Heater Systems: Other Mercury Villager II

A/C-HEATER SYSTEM (MAIN)

The main system uses blend air method to provide conditioned air to vehicle interior. Temperature blending is controlled by temperature blend door, which regulates amount of cool airflow through or around heater core. An internal microcomputer analyzes inputs from various sources to provide optimum system performance. The A/C pressure (high and low) switches turn compressor on and off to maintain desired cooling and prevent evaporator freezing.

A/C-HEATER SYSTEM (AUXILIARY)

The auxiliary system is available as an option on Villager. System consists of an auxiliary A/C-heater unit and connecting duct work. The auxiliary unit is located on right rear side of vehicle. System is a blend air design. Electric actuators control temperature blend door and vent door to direct airflow.

The auxiliary system operates in conjunction with the main system. While the auxiliary system has its own blower motor, heater core, evaporator core, vent doors and control panel, it shares the compressor, suction accumulator-drier and condenser core with main system.

CLIMATE CONTROL PANEL (MAIN)

The Electronic Automatic Temperature Control (EATC) module has 3 main features: temperature control, airflow control, and blower motor control. (Scheme 31) System can operate in full automatic mode or it can be manually operated. Press AUTOMATIC button to operate system in full automatic mode. Press A/C button to manually operate system. An auxiliary blower control lever provides rear (auxiliary) blower motor speed control.

Airflow Mode Control

Airflow mode can be controlled automatically or manually. Under automatic airflow control, air is directed to appropriate ducts based on sensor inputs, temperature selection and current state. Manual airflow selection can be accomplished without leaving automatic temperature and blower controls. The following manual override mode buttons are available: OFF, defrost/floor, defrost, panel, panel/floor and floor. (Scheme 31)

Blower Motor Control

Blower motor speed can be manually or automatically controlled. Under automatic operation, blower speed is varied to accommodate automatic functions in system. Under manual operation, blower speed is determined by position of blower speed thumbwheel. (Scheme 31) Blower motor speed will remain constant at selected speed setting.

Temperature Control

The selected or target temperature is automatically maintained by the EATC module. AUTO and selected temperature will be shown in display window. Temperature selection can be adjusted between a maximum cool setting of 60°F (15°C) and maximum heat setting of 90°F (32°C) by pressing TEMP button. (Scheme 31)

Auxiliary Blower Control Lever (Front Mounted)

Lever controls blower motor speed of auxiliary system. Lever has 6 positions: OFF, REAR, 1 (low), 2 (medium-low), 3 (medium-high) and 4 (high). (Scheme 31) When not in OFF or REAR position, lever overrides speed setting of blower switch on auxiliary control panel. Placing lever in REAR position allows the auxiliary system to be controlled from auxiliary (rear) climate control panel. Placing lever in OFF position completely turns off auxiliary system.

Scheme 31

Blower Control Knob (Rear Mounted)

Switch operates auxiliary blower motor at 4 different speeds: low, medium-low, medium-high, and high. (Scheme 32) Auxiliary system blower speed can be controlled by knob only when front-mounted auxiliary system blower control lever (on front climate control panel) is in REAR position.

Scheme 32

BLOWER MOTOR CIRCUIT (MAIN)

Blower Motor

Power to blower motor is controlled by a normally open blower motor relay, located in instrument panel fuse/relay panel. With ignition on, blower motor relay is energized, providing power to blower speed controller to control blower motor speed.

Blower Speed Controller (BSC)

BSC provides a variable control signal voltage, which is turned on and off many times per second by EATC module to control blower motor speed. BSC has a delay function, accomplished by varying the ratio of time on (4.6 volts) to time off (0 volts), to gradually increase and decrease blower motor speed. Current flows through the blower motor and power transistor to ground.

Power to blower motor is controlled by normally open auxiliary (rear) blower motor relay, auxiliary (rear) blower motor switch relay, front-mounted auxiliary blower control lever and rear-mounted auxiliary blower control knob. When ignition is on, blower motor relay is energized, providing power to blower motor power circuit. Then depending on position of auxiliary blower control lever (on front climate control panel), blower motor ground will either be provided through auxiliary (rear) blower motor switch relay or front-mounted auxiliary blower motor switch.

Blower Motor Resistor

Resistor is mounted on the auxiliary A/C-heater unit, located on right rear side of vehicle. Blower speed is varied by varying the resistance in the circuit through a series of resistors.

A/C Dual Pressure Switch

Dual pressure cut-out switch, located on compressor manifold, monitors refrigerant pressure. This information is sent to Powertrain Control Module (PCM), which uses this information to control cooling fan and A/C compressor clutch.

When discharge pressure decreases to about 250 psi (17.5 kg/cm 2 ), dual pressure cut-out switch contacts will close, energizing A/C compressor (magnetic) clutch coil. When discharge pressure increases to about 405-445 psi (28.5-31.3 kg/cm 2 ), dual pressure cut-out switch contacts will open, de-energizing A/C compressor clutch coil.

When A/C is turned on, cooling fan operates at low speed. When discharge pressure is about 305-345 psi (21.4-24.3 kg/cm 2 ), dual pressure cut-out switch contacts will close and cooling fan will operate at high speed. When discharge pressure decreases to 230-270 psi (16.2-19.0 kg/cm 2 ), dual pressure cut-out switch contacts will open and cooling fan will operate at low speed.

A/C Relay

A/C relay, located in engine compartment fuse/relay panel, supplies power to compressor. The Powertrain Control Module (PCM) controls relay based on input signals from A/C high pressure switch and A/C low pressure switch.

A/C Clutch Cycling Switch

Clutch cycling pressure switch is located on top of suction accumulator-drier and monitors refrigerant pressure. This information is sent to Powertrain Control Module (PCM). When suction pressure is about 22 psi (1.5 kg/cm 2 ), switch contacts open, and A/C compressor (magnetic) clutch coil is de-energized. When suction pressure increases to about 47 psi (3.3 kg/cm 2 ) or more, switch contacts close, and A/C compressor clutch coil is energized.

Ambient temperatures less than 48°F (9°C) will prevent suction pressure from increasing enough to close switch contacts. Proper operation of clutch cycling pressure switch prevents evaporator icing, which would block airflow through evaporator fins.

Fresh/Recirculated Air Door

Actuator is located behind right side of instrument panel, on plenum. Actuator uses output signal from EATC module to position fresh/recirculated air door. An internal potentiometer in the actuator sends variable voltage back to EATC module to indicate door position.

Temperature Blend Door (Main System)

Temperature blend door actuator is located on evaporator housing, below center duct. EATC module sends output signal to actuator to position temperature blend door. An internal potentiometer in the actuator sends variable voltage back to EATC module to indicate door position.

Fixed Orifice Tube

The fixed orifice tube provides restriction between high and low pressure liquid refrigerant. Orifice tube meters liquid refrigerant flow to evaporator core. Orifice tube is located in condenser-to-evaporator line. Filter screens at inlet and outlet ports prevent clogging while "O" rings prevent liquid refrigerant from by-passing orifice tube.

Pressure Relief Valve

The pressure relief valve, located on compressor manifold and tube, protects refrigerant system from excessive pressure. If high side pressure exceeds 450 psi (31.6 kg/cm 2 ), valve opens, venting refrigerant to atmosphere. After excessive pressure is relieved, valve closes to prevent total loss of refrigerant.

Ambient Temperature Sensor

Sensor is located in front of condenser core, attached to hood latch support. Sensor thermistor measures ambient (outside) temperature and sends a resistance value to EATC module.

ATC Sensor

Note. Automatic Temperature Control (ATC) sensor may also be referred to as in-car temperature sensor.

ATC sensor is located in right center of instrument panel, behind radio. Sensor hose is connected between evaporator housing and sensor. Sensor hose draws air from air stream between evaporator housing and sensor to create suction. Suction draws air inside vehicle into ATC sensor, across thermistor. Sensor thermistor measures in-car air temperature and sends this information to EATC module.

Coolant Temperature Sensor

Coolant temperature sensor is a thermistor-type sensor, located on heater inlet hose between engine and heater core. Sensor tells EATC module when engine coolant is warm enough to provide warm discharge air to passenger compartment.

Sunload Sensor

Sunload sensor is located on left side of instrument panel. Sunload sensor is a photovoltaic (sunlight sensitive) diode, which monitors sunlight intensity within the vehicle and sends a signal to the EATC module.

ELECTRIC ACTUATORS

Actuators are automatically calibrated during system self-diagnostics. To enter self-diagnostics, see ENTERING SELF-DIAGNOSTICS under SELF-DIAGNOSTICS.

Mechanical

Check for coolant leaks, refrigerant leaks, damaged or loose accessory drive belt, damaged compressor and/or clutch, damaged refrigerant hoses, stuck/binding actuator mechanisms, stuck/binding doors and linkages, cracked/kinked coolant control solenoid valve hoses, and damaged ducts.

Electrical

Check for blown fuses, damaged/corroded blower motor relay, blower motor switch relay (auxiliary), blower motor resistor (auxiliary) and/or A/C relay, damaged blower motor switch, damaged blower motor, damaged actuators, damaged/misrouted wiring circuits, and damaged/disconnected connectors.

SYSTEM TESTS

A/C SYSTEM PERFORMANCE

1. Park vehicle out of direct sunlight. Connect manifold gauge set to service valves. Close all doors and windows. Insert thermometer in center vent.
2. Place climate control panel in recirculated air mode and blower motor on highest speed. Run engine at 1500 RPM for 10 minutes to allow A/C system to stabilize.
3. Temperature must be 33-47°F (.6-8°C) at center vent. Ensure high side pressure is within specification. See «A/C SYSTEM HIGH SIDE PRESSURE SPECIFICATIONS»(ref-91346-S34609507372001030900000) table. Low side pressure should remain constant at 23.5-47 psi (1.65-3.30 kg/cm 2 ) throughout normal operating range.

A/C SYSTEM HIGH SIDE PRESSURE SPECIFICATIONS

A/C-HEATER UNIT

Note. The auxiliary system A/C-heater unit is removed as a complete assembly. Only blower motor and blower motor resistor can be serviced through access panel.

HEATER CORE

Note. Removal and installation procedure for rear heater core is not available from manufacturer.