HVAC Control System - General Information: Overview Mercury Montego III

Principles of Operation

There are 4 main principles involved with the basic theory of operation

1. Heat transfer
2. Latent heat of vaporization
3. Relative humidity
4. Effects of pressure

Normal Operation

Under normal operation, the in-vehicle air temperature sensor receives a ground from the electronic automatic temperature control (EATC) module through circuit 3051 (BK/YE). A 5-volt reference voltage is supplied to the in-vehicle air temperature sensor from the EATC module through circuit 3050 (WH/OG).

Under normal operation, the ambient air temperature sensor receives a ground from the EATC module through circuit 3051 (BK/YE). A 5-volt reference voltage is supplied to the ambient air temperature sensor from the EATC module through circuit 3060 (GY/RD).

Under normal operation, the solar radiation sensor receives a ground through circuit 3051 (BK/YE). A 5-volt reference voltage is supplied to the solar radiation sensor from the EATC module through circuit 468 (BN).

Under normal operation, to rotate the air inlet door actuator clockwise, the EMTC module or EATC module supplies voltage to the air inlet air inlet door actuator motor through the circuit 1990 (WH/LB), and supplies ground through circuit 1991 (LB/WH). To rotate the air inlet door actuator counterclockwise, the EATC module reverses the voltage and ground circuits.

Note. EATC only.

The air inlet door actuator feedback resistor is supplied a ground from the EATC module through circuit 438 (RD/WH) and a 5-volt reference voltage on circuit 436 (RD/LG). The EATC module reads the voltage on the air inlet door actuator feedback circuit 3053 (BN/WH) to determine the air inlet door actuator position by the position of the actuator feedback resistor wiper arm.

Under normal operation, to rotate the mode door actuator clockwise, the EMTC module or EATC module supplies voltage to the Floor/Defrost/Panel mode door actuator motor through the circuit 1989 (OG/LB), and supplies ground through circuit 1988 (BN/OG). To rotate the mode door actuator counterclockwise, the EMTC module or EATC module reverses the voltage and ground circuits.

The mode door actuator feedback resistor is supplied a ground from the EMTC module or EATC module through circuit 438 (RD/WH) and a 5-volt reference voltage on circuit 436 (RD/LG). The EMTC module or EATC module reads the voltage on the mode door actuator feedback circuit 1982 (LB/BK) to determine the mode door actuator position by the position of the actuator feedback resistor wiper arm.

Under normal operation, the EATC module receives a ground through circuit 1203 (BK/LB). The EATC module is supplied constant battery voltage through circuit 483 (RD) and ignition switched voltage through circuit 1566 (RD/YE).

Under normal operation, the EATC module receives a ground through circuit 1203 (BK/LB). The EATC module is supplied constant battery voltage through circuit 483 (RD) and ignition switched voltage through circuit 1566 (RD/YE).

Note. For a complete explanation of the EATC system functions, REFER to DESCRIPTION AND OPERATION .

Under normal operation, warm coolant flows from the engine through the heater core and back to the engine.

Under normal operation, when A/C is requested, a message is sent over the MSCAN bus to the instrument cluster, then from the instrument cluster through the HSCAN bus to the PCM (EATC systems) or a voltage is sent to the instrument cluster through circuit 1424 (TN/BK) then a message from the instrument cluster through the HSCAN bus to the PCM (EMTC systems).

Ignition voltage for the A/C clutch relay switch is provided through circuit 3028 (DB/YE). When the PCM energizes the relay, ignition voltage is supplied to the A/C clutch through circuit 1810 (LG/OG). Ground is supplied for the A/C clutch through circuit 1205 (BK).

Under normal operation, when A/C is requested, a message is sent over the MSCAN bus to the instrument cluster, then from the instrument cluster through the HSCAN bus to the PCM (EATC systems) or a voltage is sent to the instrument cluster through circuit 1424 (TN/BK) then a message from the instrument cluster through the HSCAN bus to the PCM (EMTC systems).

Ignition voltage for the A/C clutch relay switch is provided through circuit 3028 (DB/YE). When the PCM energizes the relay, ignition voltage is supplied to the A/C clutch through circuit 1810 (LG/OG). Ground is supplied for the A/C clutch through circuit 1205 (BK).

Under normal operation, to rotate the blend door actuator clockwise, the EMTC module or EATC module supplies voltage to the Blend door actuator motors through the door actuator feed A circuits, and supplies ground through the door actuator feed B circuits. To rotate the blend door actuator counterclockwise, the EMTC module or EATC module reverses the voltage and ground circuits.

The blend door actuator feedback resistors are supplied a ground from the EMTC module or EATC module by the blend door actuator return circuits and a 5-volt reference voltage on the blend door actuator reference circuits. The EMTC module or EATC module reads the voltage on the blend door actuator feedback circuits to determine the blend door actuator position by the position of the actuator feedback resistor wiper arm.

Under normal operation, the blower motor relay coil receives ignition voltage through circuit 296 (WH/VT). The coil receives ground from the EMTC module through circuit 1322 (BN/WH) if any function selector position but OFF is selected. Voltage is supplied to the relay switch contact through circuit 364 (BK/LG). When the relay coil is energized, voltage is delivered to the blower motor through circuit 261 (OG/BK). Ground for the blower motor is provided through circuit 752 (YE/RD) from the blower resister or the blower switch (HI). The blower resister and blower switch is grounded through circuit 1205 (BK).

Under normal operation, the blower motor is provided a ground from the blower resistor through circuit 752 (YE/RD). The resistor gets a ground from circuit 1205 (BK) in the lowest blower setting. In MED-LO and MED-HI the resistor gets a ground from the blower motor switch through circuit 260 (RD/OG) or 269 (LB/OG), depending on selected speed. In HI, the blower motor is grounded directly through the blower motor switch from circuit 752 (YE/RD) to circuit 1205 (BK). The blower switch receives its ground from circuit 1205 (BK).

Under normal operation, the blower motor relay coil receives a ground from the EATC module through circuit 1322 (BN/WH). The coil receives voltage ignition voltage through circuit 296 (WH/VT). Voltage is supplied to the relay switch contact through circuit 364 (BK/LG). When the relay coil is energized, voltage is delivered to the blower motor and the blower motor control module through circuit 261 (OG/BK). Ground for the motor is provided through circuit 515 (BK/WH) from the blower control module. Ground for the blower control module is provided by circuit 1205 (BK). The EATC module sends pulse width modulated signal to the blower control module through circuit 1120 (BK/WH) to control the blower speed.

Under normal operation, the blower motor relay coil receives a ground from the EATC module through circuit 1322 (BN/WH). The coil receives voltage ignition voltage through circuit 296 (WH/VT). Voltage is supplied to the relay switch contact through circuit 364 (BK/LG). When the relay coil is energized, voltage is delivered to the blower motor and the blower motor control module through circuit 261 (OG/BK). Ground for the motor is provided through circuit 515 (BK/WH) from the blower control module. Ground for the blower control module is provided by circuit 1205 (BK). The EATC module sends pulse width modulated signal to the blower control module through circuit 1120 (BK/WH) to control the blower speed.

Under normal operation, the auxiliary blower motor relay coil receives ignition voltage through circuit 181 (BN/OG). The coil receives ground from the electronic automatic temperature control (EATC) module through circuit 1371 (TN/OG) if any auxiliary blower speed but OFF is selected. Voltage is supplied to the relay switch contact through circuit 1004 (LB/RD). When the relay coil is energized, voltage is delivered to the blower motor through circuit 536 (BK/LG). Ground for the blower motor is provided through circuit 515 (OG/RD) from the blower motor resistor. The blower resistor is grounded through circuit 1205 (BK).

Under normal operation, ground for the blower motor is provided through circuit 515 (OG/RD) from the blower motor resistor. The blower resistor is grounded through circuit 1205 (BK). The blower motor speed relay coils are supplied through circuit 1004 (LB/RD). Blower motor speed is received by the electronic automatic temperature control (EATC) module from the rear auxiliary control through circuit 1125 (BN). Reference voltage for the blower speed selector resistor is provided by the EATC module through circuit 1381 (WH/LB). The auxiliary blower motor relay coil receives ground from the EATC module through circuit 1371 (TN/OG) if any blower speed but OFF is selected.

In LO, ground for the blower motor is provided through the blower motor resistor.

In MED-LO, blower motor speed relay 3 is grounded by the EATC module through circuit 1372 (PK/BK). Blower motor ground circuit 515 (OG/RD) is connected through one half of the blower motor resistor to circuit 751 (DB/WH). Circuit 751 (DB/WH) is connected through blower motor speed relay 3 to the blower motor resistor through circuit 752 (YE/RD). The blower resistor is grounded through circuit 1205 (BK).

In MED-HI, blower motor relay 2 is grounded by the EATC module through circuit 1373 (GY/YE). Blower motor ground circuit 515 (OG/RD) is connected through blower motor speed relay 2 to circuit 751 (DB/WH). Circuit 751 (DB/WH) is connected through one half of the blower motor resistor to the blower motor resistor to ground circuit 1205 (BK).

In HI, blower motor speed relays 2 and 3 are grounded by the EATC module through circuit 1372 (PK/BK) and 1373 (GY/YE). Blower motor ground circuit 515 (OG/RD) is connected through blower motor speed relay 2 to circuit 751 (DB/WH). Circuit 751 (DB/WH) is connected through blower motor speed relay 3 to the blower motor resistor ground circuit 1205 (BK) by circuit 752 (YE/RD).

Under normal operation, to rotate the mode door actuator clockwise, the EATC module supplies voltage to the auxiliary temperature door actuator through the circuit 1376 (BK/LB), and supplies ground through circuit 1375 (PK/YE). To rotate the auxiliary temperature door actuator counterclockwise, the EATC module reverses the voltage and ground circuits.

The auxiliary temperature door actuator feedback resistor is supplied a ground from the EATC module through circuit 1377 (TN/LG) and a 5-volt reference voltage on circuit 1381 (WH/LB). The EATC module reads the voltage on the auxiliary temperature door actuator feedback circuit 1378 (GY/WH) to determine the auxiliary temperature door actuator position by the position of the actuator feedback resistor wiper arm.

Under normal operation, to rotate the mode door actuator clockwise, the EATC module supplies voltage to the auxiliary panel/floor door actuator through the circuit 1380 (TN/YE), and supplies ground through circuit 1379 (PK/LB). To rotate the auxiliary panel/floor door actuator counterclockwise, the EATC module reverses the voltage and ground circuits.

The auxiliary panel/floor door actuator feedback resistor is supplied a ground from the EATC module through circuit 1377 (TN/LG) and a 5-volt reference voltage on circuit 1381 (WH/LB). The EATC module reads the voltage on the auxiliary panel/floor door actuator feedback circuit 1382 (BK/OG) to determine the auxiliary panel/floor door actuator position by the position of the actuator feedback resistor wiper arm.

Under normal operation, the panel/floor and cool/warm signal is received by the EATC module from the rear auxiliary control through circuit 1121 (DG/YE). The blower speed signal is received by the EATC from the rear auxiliary control through circuit 1125 (BN). Reference voltage for the auxiliary controls signal resistor is provided by the EATC module through circuit 1381 (WH/LB). Ground for the auxiliary controls signal resistor is provided by the EATC module through circuit 1377 (TN/LG).

Refrigerant Identification

1. Follow the instructions included with the refrigerant identifier to obtain the sample for testing.
2. The scan tool will display one of the following: If the purity level of R-134a is 98% or greater by weight, the green "PASS" light emitting diode (LED) will light. The weight concentrations of R-134a, R-12, R-22, hydrocarbons and air will be displayed on the digital display. If refrigerant R-134a does not meet the 98% purity level, the red "FAIL" LED will light and an alarm will sound alerting the user of potential hazards. The weight concentrations of R-134a, R-12, R-22 and hydrocarbons will be displayed on the digital display. If hydrocarbon concentrations are 2% or greater by weight, the red "FAIL" LED will light, "Hydrocarbon High" will be displayed on the digital display, and an alarm will sound alerting the user of potential hazards. The weight concentrations of R-134a, R-12, R-22 and hydrocarbons will also be displayed on the digital display.
3. The percentage of air contained in the sample will be displayed if the R-134a content is 98% or greater. The scan tool eliminates the effect of air when determining the refrigerant sample content because air is not considered a contaminant, although air can affect A/C system performance. When the scan tool has determined that a refrigerant source is pure (R-134a is 98% or greater by weight) and air concentration levels are 2% or greater by weight, the scan tool will prompt the user if an air purge is desired.
4. If contaminated refrigerant is detected, repeat the refrigerant identification test to verify that the refrigerant is indeed contaminated.