Engine Coolant through A/C Cycle
AIR TEMPERATURE DESCRIPTION AND OPERATIONThe air temperature controls are divided into 4 areas:
- HVAC Control Components
- Heating and A/C Operation
- Engine Coolant
- A/C Cycle
ENGINE COOLANT
Engine coolant is the essential element of the heating system. The thermostat controls the normal engine operating coolant temperature. The thermostat also creates a restriction for the cooling system that promotes a positive coolant flow and helps prevent cavitation.
Coolant enters the heater core through the inlet heater hose, in a pressurized state. The heater core is located inside the HVAC module. The ambient air drawn through the HVAC module absorbs the heat of the coolant flowing through the heater core. Heated air is distributed to the passenger compartment, through the HVAC module, for passenger comfort. Opening or closing the air temperature door controls the amount of heat delivered to the passenger compartment. The coolant exits the heater core through the return heater hose and recirculated back through the engine cooling system.
COOLING FAN OPERATION
The cooling system includes 2 dual speed, engine cooling fan motors, both of which have drive fans with 5 asymmetrical blades to reduce air noise. The fans remove heat from both the engine coolant flowing through the radiator and the refrigerant flowing through the air conditioning condenser. The fan and motor assemblies are mounted on a common shroud, which in turn is mounted onto the engine side of the radiator. The A/C condenser is mounted to the front of the radiator.
The fan motors are 12-volt, dual speed types. The internal construction of the fan motor consists of 4 brushes and 4 permanent magnets. A 3-wire pigtail harness is permanently attached to both motors and is attached to the polypropylene fan shroud at 2 locations by integral clips moulded as part of the shroud. Both motor harnesses are connected directly to the engine harness through a 3-pin sealed connector. This enables individual removal of the left and right fan and motor assemblies when necessary. The 2 electrical connectors are attached to the shroud by way of slide lock clips. Each motor is attached to the polypropylene fan shroud by 3 bolts installed at the threaded mounting flanges, which protrude symmetrically from the rear of the fan motor housing. The enclosed fan motor housing is constructed of yellow zinc coated steel. A drain hole is located in the bottom of the housing to allow for breathing and draining of any moisture ingress. Both fan motors rotate in an anti-clockwise direction when viewed from the fan motor side. Both fan and motor assemblies are balanced as a unit. Fan blades must not be separated from their respective motors. Fan motors and blades are serviced only as an assembled unit. The central nut attaching the fan blade to the motor shaft has a left-hand thread.
Each fan motor harness has 1 positive and 2 negative wires. To reduce the heat burden on the electrical connectors, the current draw is directed through separate negative terminals at the connector for each fan motor. The positive wire permanently connects battery voltage to the 2 positive brushes of each fan motor. The negative wires are each connected to 1 negative brush. When 1 negative wire per fan motor is grounded via the engine cooling fan relay 1, both cooling fan motors will operate at low speed. When both negative wires of each fan motor are grounded via the engine cooling fan relay 2, both cooling fan motors will operate at high speed.
Suppression capacitors located at the fan motor brush holders are incorporated. These suppression capacitors help eliminate fan motor noise through the radio speakers. If these capacitors are open, noise will be present through the radio speakers. If either of these capacitors were shorted to ground, the fan motors could run continuously or the fuses could fail. These capacitors are not serviced separately, the motor assembly must be replaced should a problem occur with either capacitor.
There are 2 relays used to control fan operation The engine cooling fan relay 1 for low speed operation and the engine cooling fan relay 2 for high speed operation. The engine cooling fan relay 1 is energized by the body control module (BCM) in response to a request from the powertrain control module (PCM). The engine cooling fan relay 2 is energized by the PCM. After the PCM requests a change in the state of engine cooing fan relay 1, the BCM will send a serial data response message back to the PCM confirming it received the message. Serial data communication between the PCM and BCM is via the powertrain interface module (PIM). The PCM determines when to enable and disable both engine cooling fan relays based on inputs from the A/C request signal, the engine coolant temperature (ECT) sensor and the vehicle speed sensor (VSS).
Stage One - Both Fans Operate at Low Speed
The engine cooling fan relay 1 is energized by the BCM in response to a request from the PCM. When the PCM determines that the engine cooling fan relay 1 should be enabled, the PCM will send a message on the Class 2 serial data circuit to the PIM. The PIM will then convert the PCM Class 2 message to a UART message and supply this UART message to the BCM, via a serial data Normal Mode Message. This message will request the BCM to supply the needed ground signal for the engine cooling fan relay 1 to operate.
After the BCM provides the ground signal for the engine cooling fan relay 1, the BCM will send a message back to the PIM confirming that the ground signal was commanded. A failure in this BCM response communication, will cause a PIM DTC to set. The engine cooling fan relay 1 will be turned ON and both fans driven at low speed when the A/C request indicates YES and either:
- Vehicle speed is less than 30 km/h (19 mph).
- A/C refrigerant pressure is greater than 1,500 kPa (218 psi).
- ECT is greater than 108°C (227°F).
- If an ECT fault is detected and a DTC is set.
- When an ECT sensor failure in conjunction with an intake air temperature (IAT) sensor failure is detected by the PCM.
- When the ignition switch is turned from ON to OFF and the ECT is above 11 3°C (235°F), the BCM continues to energies the engine cooling fan relay 1 for 4 minutes. The low-speed cooling fan run-on time has a minimum default value of 30 seconds.
The low speed cooling fan operation is disabled when the engine cooling fan relay 1 is de-energized by the BCM via a request from the PCM. The PCM will request low speed fan disable via serial data communication to the BCM via the PIM. After the PCM requests a change in the state of engine cooling fan relay 1, the BCM will send a serial data response message back to the PCM confirming it received the message.
The engine cooling fan relay 1 will be turned OFF when any of the following conditions have been met:
- An A/C request is indicated (YES) with A/C refrigerant pressure less than 1,170 kPa (170 psi), vehicle speed greater than 50 km/h (31 mph) and the ECT less than 108°C (227°F).
- An A/C request is not indicated (NO) and the ECT is less than 104°C (219°F).
Stage Two - Both Fans Operate at High Speed
The engine cooling fan relay 2 is controlled by the PCM. The PCM will only turn ON the engine cooling fan high speed relay fan if the engine cooling fan relay 1 has been ON for 2 seconds and the following conditions are satisfied:
- There is a BCM to PIM message response fault which will cause a PIM DTC to set.
- An ECT sensor fault is detected and a DTC is set.
- The ECT is greater than 113°C (235°F).
- The A/C refrigerant pressure is greater than 2,400 kPa (348 psi).
The engine cooling fan relay 2 will be turned OFF when any of the following conditions have been met:
- The ECT is less than 108.5°C (227.3°F).
- An A/C request is not indicated (NO).
- An A/C request is indicated (YES) and the A/C refrigerant pressure is less than 1,900 kPa (276 psi).
If the engine cooling fan relay 1 was OFF when the criteria was met to activate engine cooling fan relay 2, stage 2 fan operation will occur 1-5 seconds after the engine cooling fan relay 1 is turned ON.
If both engine cooling fan relays are ON, the PCM will turn OFF engine cooling fan relay 2 when any of the following conditions have been met:
- The engine coolant temperature is less than 108°C (227°F).
- An A/C request is not indicated (NO).
- An A/C request is indicated (YES) and the A/C refrigerant pressure is less than 1,900 kPa (276 psi).
The Stage 2 cooling fan operation has a minimum run-on time function of 30 seconds. Both cooling fans will be turned OFF if the vehicle speed is greater than 104 km/h (65 mph). Dependent upon input signals, ambient temperature, etc. the vehicle speed when all cooling fans will be turned OFF, is variable.
A/C Cycle
Refrigerant is the key element in an air conditioning system. R-134a is presently the only EPA approved refrigerant for automotive use. R-134a is a very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.
The A/C system used on this vehicle is a non-cycling system. Non-cycling A/C systems use a high pressure switch to protect the A/C system from excessive pressure. The high pressure switch will OPEN the electrical signal to the compressor clutch, if the refrigerant pressure becomes excessive. After the high and the low sides of the A/C system pressure equalize, the high pressure switch will CLOSE. This completes the electrical circuit to the compressor clutch. The A/C system is also mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continues to rise, the high pressure relief will pop open and release refrigerant from the system.
The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat. The refrigerant is discharged from the compressor through the discharge hose, and forced through the condenser and then through the balance of the A/C system.
Compressed refrigerant enters the condenser at a high-temperature, high-pressure vapor state. As the refrigerant flows through the condenser, the heat is transferred to the ambient air passing through the condenser. Cooling causes the refrigerant to condense and change from a vapor to a liquid state. The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and aluminum cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line to the thermal expansion valve (TXV).
The TXV is located at the evaporator inlet. The TXV is the dividing point for the high and the low pressure sides of the A/C system. As the refrigerant passes through the TXV, the pressure on the refrigerant is lowered, causing the refrigerant to vaporize at the TXV. The TXV also measures the amount of liquid refrigerant that can flow into the evaporator.
Refrigerant exiting the TXV flows into the evaporator core in a low-pressure, liquid state. Ambient air is drawn through the HVAC module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant to boil inside the evaporator core. The boiling refrigerant absorbs heat from the ambient air and draws moisture onto the evaporator. The refrigerant exits the evaporator through the suction line and flows back to the compressor in a vapor state, completing the A/C cycle of heat removal. At the compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.
The conditioned air is distributed through the HVAC module for passenger comfort. The heat and moisture removed from the passenger compartment condenses, and discharges from the HVAC module as water.