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Home/Mercury/Monterey/Mercury Monterey VIII (2003-2007)/Repair manual/Automatic HVAC System/HVAC Control System - General Information: Overview
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HVAC Control System - General Information: Overview Mercury Monterey VIII

Automatic HVAC System ~2990 words

Principles of Operation

There are four 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 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) (LH) and circuit 476 (BN/YE) (RH).

Under normal operation, the air inlet door actuator motor is supplied voltage or ground on circuit 1991 (LB/WH), depending on desired actuator rotation, by the EMTC module or EATC module. The EMTC module or EATC module then supplies the appropriate voltage or ground to the other side of the actuator motor on circuit 1990 (WH/LB).

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 motors 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 1978 (BN/LG) and a 5-volt reference voltage on circuit 1977 (YE/BK). 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 1001 (WH/YE) and ignition switched voltage through circuit 1003 (GY/YE).

Pinpoint Test F: The EATC System is Inoperative, Intermittent or Incorrect Operation

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

Under normal operation, the EATC module receives a ground through circuit 1203 (BK/LB). The EATC module is supplied constant battery voltage through circuit 1001 (WH/YE) and ignition switched voltage through circuit 1003 (GY/YE).

  1. F1 VERIFY AUTOMATIC OPERATION Key in ON position. With the engine running, press the AUTOMATIC button. Does the indicator above the AUTO button illuminate and the selected temperature for both the driver and passenger appear in the display window? Yes : GO to F2 . No : GO to F11 .
  2. F2 PERFORM THE EATC MODULE SELF-TEST Key in ON position. CARRY OUT the EATC module self-test. Refer to the «ELECTRONIC AUTOMATIC TEMPERATURE CONTROL MODULE ON-DEMAND SELF-TEST»(ref-234501-S24622288872006061000000) . Record the DTCs displayed, if any. Were any DTCs displayed as a result of the EATC self-test? Yes : REFER to «ELECTRONIC AUTOMATIC TEMPERATURE CONTROL (EATC) MODULE DIAGNOSTIC TROUBLE CODE (DTC) INDEX»(ref-234501-S25522424112006061000000) . CARRY OUT the necessary diagnosis and REPAIR as required. No : GO to F3 .
  3. F3 CHECK THE VACUUM FLUORESCENT DISPLAY Exit self-test by pressing the DEFROST button. Observe the button indicators and function symbols displayed on the vacuum fluorescent display while changing the temperature, blower speed and functions. Are the display and indicators correct and complete without any missing elements? Yes : GO to F4 . No : INSTALL a new EATC module. TEST the system for normal operation.
  4. F4 CHECK THE BLOWER MANUAL OVERRIDE OPERATION Press the blower motor speed override control fully up and fully down. Does the blower motor speed increase from low speed to high and high speed to low? Yes : GO to F5 . No : If the blower motor is inoperative, GO to «PINPOINT TEST M»(ref-234501-S33053742722006061000000) . If the blower motor does not operate correctly, GO to «PINPOINT TEST N»(ref-234501-S33771826612006061000000) .
  5. F5 VERIFY THE DEFROST OVERRIDE OPERATION Press the override button for DEFROST operation. Is outside air being discharged from the windshield defroster nozzle and the side window demisters? Yes : GO to F6 . No : GO to «PINPOINT TEST D»(ref-234501-S18069379122006061000000) .
  6. F6 VERIFY THE FLOOR OVERRIDE OPERATION Press the override button for FLOOR operation. Is outside air being discharged from the floor duct? Yes : GO to F7 . No : GO to «PINPOINT TEST D»(ref-234501-S18069379122006061000000) .
  7. F7 VERIFY THE PANEL OVERRIDE OPERATION Press the override button for PANEL operation. Is outside air being discharged from the instrument panel registers? Yes : GO to F8 . No : GO to «PINPOINT TEST D»(ref-234501-S18069379122006061000000) .
  8. F8 VERIFY THE A/C CLUTCH DOES NOT ENGAGE IN THE PANEL MODE In PANEL operation and the A/C OFF, listen for the compressor clutch to engage. Does the A/C clutch engage with the PANEL override button pressed? Yes : GO to «PINPOINT TEST J»(ref-234501-S01416804902006061000000) . No : GO to F9 .
  9. F9 VERIFY A/C CLUTCH ENGAGEMENT IN THE A/C MODE Make sure the ambient air temperature is above 6°C (43°F). Press the override button for A/C operation. Does the A/C clutch engage when the A/C override button is pressed? Yes : GO to F10 . No : GO to «PINPOINT TEST I»(ref-234501-S10137456382006061000000) .
  10. F10 VERIFY THE RECIRC OVERRIDE OPERATION Press the PANEL and RECIRC override buttons. Is recirculated air being discharged from the instrument panel registers? Yes : The test is complete. The system is functioning normally. No : GO to «PINPOINT TEST C»(ref-234501-S30014967562006061000000) .
  11. F11 CHECK THE EATC MODULE FUNCTIONS Press each function button and observe the display. Does the EATC perform and display any functions? Yes : INSTALL a new EATC module. TEST the system for normal operation. No : GO to F12 .
  12. F12 CHECK CIRCUIT 1203 (BK/LB) FOR AN OPEN Key in OFF position. Disconnect: EATC Module C228a. Measure the resistance between the EATC module C228a-1, circuit 1203 (BK/LB) and ground. Is the resistance less than 5 ohms? Yes : GO to F13 . No : REPAIR circuit 1203 (BK/LB). TEST the system for normal operation.
  13. F13 CHECK CIRCUITS 1001 (WH/YE) AND 1003 (GY/YE) FOR AN OPEN Key in ON position. Measure the voltage between the EATC module C228a-26, circuit 1001 (WH/YE), C228a-14, circuit 1003 (GY/YE) and ground. Is the voltage greater than 10 volts? Yes : INSTALL a new EATC module. TEST the system for normal operation. No : REPAIR circuit 1001 (WH/YE) or 1003 (GY/YE) for an open. TEST the system for normal 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 signal is sent from the control module to the Smart Junction Box (SJB) through circuit 1397 (GY/WH) (Single-zone EMTC only) or over the SCP BUS (Dual-zone EATC and EMTC only). The SJB sends a message over the SCP bus to the PCM. Voltage is supplied to the A/C cycling switch by circuit 298 (VT/OG) and to the PCM through circuit 347 (BK/YE).

The PCM provides a ground for the A/C clutch relay coil through circuit 331 (PK/YE). The A/C clutch relay coil receives ignition voltage through circuit 391 (RD/YE). Ignition voltage for the A/C clutch relay switch is provided through circuit 931 (OG). When the relay is activated, ignition voltage is supplied to the A/C clutch solenoid through circuit 883 (PK/LB). Ground is supplied for the A/C clutch through circuit 1205 (BK).

Under normal operation, when A/C is requested a signal is sent from the control module to the Smart Junction Box (SJB) through circuit 1397 (GY/WH) (Single-zone EMTC only) or over the SCP BUS (Dual-zone EATC and EMTC only). The SJB sends a message over the SCP bus to the PCM. Voltage is supplied to the A/C cycling switch by circuit 298 (VT/OG) and to the PCM through circuit 347 (BK/YE).

The PCM provides a ground for the A/C clutch relay coil through circuit 331 (PK/YE). The A/C clutch relay coil receives ignition voltage through circuit 391 (RD/YE). Ignition voltage for the A/C clutch relay switch is provided through circuit 931 (OG). When the relay is activated, ignition voltage is supplied to the A/C clutch solenoid through circuit 883 (PK/LB). 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, when blower operation is requested a signal is sent from the control module to the Smart Junction Box (SJB) through circuit 1398 (PK/WH) (Single-zone EMTC only) or over the SCP BUS (Dual-zone EMTC only). The SJB sends a message over the SCP bus to the PCM.

The blower motor relay coil receives ignition voltage through circuit 298 (VT/OG). The coil receives ground from the Smart Junction Box (SJB) through circuit 1322 (BN/WH) if any 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 371 (PK/WH). Ground for the blower motor is provided through circuit 261 (OG/BK) from the blower resistor or the blower switch (HI). The blower resistor 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 261 (OG/BK). The blower motor resistor gets a ground from circuit 1205 (BK) in the lowest blower setting. In MED-LO and MED-HI the resistor gets a ground through circuit 269 (LB/OG) or 260 (RD/OG), depending on selected speed. In HI, the blower motor is grounded directly through the blower motor switch from circuit 261 (OG/BK) to circuit 1205 (BK). The blower switch receives its ground from circuit 1205 (BK).

Under normal operation, when blower operation is requested a signal is sent from the control module to the Smart Junction Box (SJB) over the SCP BUS. The SJB sends a message over the SCP bus to the PCM.

The blower motor relay coil receives a ground from the Smart Junction Box (SJB) through circuit 1322 (BN/WH). The coil receives voltage through circuit 298 (VT/OG). 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 371 (PK/WH). Ground for the motor is provided through circuit 261 (OG/BK) 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, when blower operation is requested a signal is sent from the control module to the Smart Junction Box (SJB) over the SCP BUS. The SJB sends a message over the SCP bus to the PCM.

The blower motor relay coil receives a ground from the Smart Junction Box (SJB) through circuit 1322 (BN/WH). The coil receives voltage through circuit 298 (VT/OG). 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 371 (PK/WH). Ground for the motor is provided through circuit 261 (OG/BK) 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 Smart Junction Box (SJB) through circuit 1371 (TN/OG) if any blower switch position but OFF is selected. Voltage is supplied to the relay switch contact through circuit 181 (BN/OG). 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 (LO and MED-LO) and the blower motor speed relay 1 (MED-HI and HI). 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 (LO and MED-LO) and the blower motor speed relay 1 (MED-HI and HI). The blower resistor is grounded through circuit 1205 (BK). The blower motor speed relay coils are supplied through circuit 1460 (RD/YE). Blower motor speed is received by the SJB from the rear auxiliary control through circuit 1349 (PK/LG). Reference voltage for the blower speed selector resistor is provided by the SJB through circuit 536 (BK/LG). The auxiliary blower motor relay coil receives ground from the Smart Junction Box (SJB) through circuit 1371 (TN/OG) if any blower switch position 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 2 is grounded by the SJB through circuit 1373 (GY/YE). 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 2 to the blower motor resistor ground circuit 1205 (BK) by circuit 752 (YE/RD).

In MED-HI, blower motor speed relay 1 is grounded by the SJB through circuit 1372 (PK/BK). 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 ground circuit 1205 (BK).

In HI, blower motor speed relays 1 and 2 are grounded by the SJB through circuit 1372 (PK/BK) and 1373 (GY/YE). Blower motor ground circuit 515 (OG/RD) is connected through blower motor speed relay 1 to circuit 751 (DB/WH). Circuit 751 (DB/WH) is connected through blower motor speed relay 2 to the blower motor resistor ground circuit 1205 (BK) by circuit 752 (YE/RD).

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

The auxiliary temperature blend door actuator feedback resistor is supplied a ground from the SJB through circuit 1382 (BK/OG) and a 5-volt reference voltage on circuit 1381 (WH/LB). The SJB reads the voltage on the auxiliary temperature blend door actuator feedback circuit 1126 (LB) to determine the auxiliary temperature blend door actuator position by the position of the actuator feedback resistor wiper arm.

Under normal operation, to rotate the auxiliary temperature blend door actuator clockwise, the SJB supplies voltage to the auxiliary temperature blend door actuator motors through the circuit 1379 (PK/LB), and supplies ground through circuit 1380 (TN/YE). To rotate the auxiliary temperature blend door actuator counterclockwise, the SJB reverses the voltage and ground circuits.

The auxiliary temperature blend door actuator feedback resistor is supplied a ground from the SJB through circuit 1125 (BN) and a 5-volt reference voltage on circuit 1124 (WH). The SJB reads the voltage on the auxiliary temperature blend door actuator feedback circuit 1131 (LG) to determine the auxiliary temperature blend 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 SJB from the rear auxiliary control through circuit 1121 (DG/YE). Reference voltage for the panel/floor and cool/warm signal resistor is provided by the SJB through circuit 1348 (GY/OG). Ground for the panel/floor and cool/warm signal resistor is provided by the SJB through circuit 1125 (BN).

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.

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