Blower Motor Relay: Description and Operation

BLOWER MOTOR RELAY - FRONT

Fig.7 Blower Motor Relay:

The blower motor relay is a International Standards Organization (ISO) mini-relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The ISO mini-relay terminal functions are the same as a conventional ISO relay. However, the ISO mini-relay terminal pattern (or footprint) is different, the current capacity is lower; and the physical dimensions are smaller than those of the conventional ISO relay. The blower motor relay is located in the Intelligent Power Module (IPM), which is in the engine compartment near the battery. See the fuse and relay layout map molded into the inner surface of the IPM cover for blower motor relay identification and location.

Fig.8 Intelligent Power Module:

The black, molded plastic case is the most visible component of the blower motor relay. Five male spade-type terminals extend from the bottom of the base to connect the relay to the vehicle electrical system, and the ISO designation for each terminal is molded into the base adjacent to each terminal. The ISO terminal designations are as shown.

The blower motor relay is an electromechanical switch that uses a low current input from the Front Control Module (FCM) to control the high current output to the blower motor resistor (manual heater- A/C control) or blower power module (ATC control). The movable common feed contact point is held against the fixed normally closed contact point by spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws the movable relay contact point away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the relay coil is de-energized, spring pressure returns the movable contact point back against the fixed normally closed contact point. The resistor or diode is connected in parallel with the relay coil in the relay, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The blower motor relay terminals are connected to the vehicle electrical system through a receptacle in the Intelligent Power Module (IPM). The inputs and outputs of the blower motor relay include:
- The common feed terminal (30) receives a battery current input from the battery through a B(+) circuit at all times.
- The coil ground terminal (85) receives a ground input through the front/rear blower motor relay control circuit only when the FCM electronically pulls the control circuit to ground.
- The coil battery terminal (86) receives a battery current input from the battery through a B(+) circuit at all times.
- The normally open terminal (87) provides a battery current output to the blower motor resistor (manual heater-A/C control) or blower power module (automatic heater-A/C control) through a fuse in the IPM on the fused front blower motor relay output circuit only when the blower motor relay coil is energized.
- The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the blower motor relay coil is de-energized.

Fig.5 Blower Motor Relay:

BLOWER MOTOR RELAY - REAR
The blower motor relay is a International Standards Organization (ISO) mini-relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The ISO mini-relay terminal functions are the same as a conventional ISO relay. However, the ISO mini-relay terminal pattern (or footprint) is different, the current capacity is lower, and the physical dimensions are smaller than those of the conventional ISO relay. The blower motor relay is located in the Intelligent Power Module (IPM), which is in the engine compartment near the battery See the fuse and relay layout map molded into the inner surface of the IPM cover for compressor clutch relay identification and location.

The black, molded plastic case is the most visible component of the blower motor relay. Five male spade-type terminals extend from the bottom of the base to connect the relay to the vehicle electrical system, and the ISO designation for each terminal is molded into the base adjacent to each terminal. The ISO terminal designations are as follows:
- 30 (Common Feed) - This terminal is connected to the movable contact point of the relay.
- 85 (Coil Ground) - This terminal is connected to the ground feed side of the relay control coil.
- 86 (Coil Battery) - This terminal is connected to the battery feed side of the relay control coil.
- 87 (Normally Open) - This terminal is connected to the normally open fixed contact point of the relay.
- 87A (Normally Closed) - This terminal is connected to the normally closed fixed contact point of the relay.

The factory-installed blower motor relay cannot be adjusted or repaired. If the relay is damaged or faulty, it must be replaced.

The blower motor relay is an electromechanical switch that uses a low current input from the Front Control Module (FCM) to control the high current output to the blower motor resistor (manual heater- A/C control) or blower power module (automatic heater-A/C control). The movable common feed contact point is held against the fixed normally closed contact point by spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws the movable relay contact point away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the relay coil is de-energized, spring pressure returns the movable contact point back against the fixed normally closed contact point. The resistor or diode is connected in parallel with the relay coil in the relay, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The blower motor relay terminals are connected to the vehicle electrical system through a receptacle in the Intelligent Power Module (IPM). The inputs and outputs of the compressor clutch relay include:
- The common feed terminal (30) receives a battery current input from the battery through a B(+) circuit at all times.
- The coil ground terminal (85) receives a ground input through the front/rear blower motor relay control circuit only when the FCM electronically pulls the control circuit to ground.
- The coil battery terminal (86) receives a battery current input from the battery through a B(+) circuit at all times.
- The normally open terminal (87) provides a battery current output to the blower motor resistor (manual heater-A/C control) or blower power module (automatic heater-A/C control) through a fuse in the IPM on the fused rear blower motor relay output circuit only when the blower motor relay coil is energized.
- The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the blower motor relay coil is de-energized.