HVAC Blower Controls Circuit Description

HVAC Blower Controls Circuit Description

Battery voltage is supplied at all times to terminal 1 of the blower relay No. 1 through CKT 440 (ORN).

The following conditions exist when the HVAC controller is in the OFF position:

* Relay No. 1 and blower relay No. 2 are de-energized.
* No voltage path exists through the relay contacts to the blower motor.

The blower motor is a variable speed motor. The blower motor runs at a speed that is proportional to the voltage supplied.

The following conditions exist when the HVAC controller is in the LOW position:

* Terminals M and L of the HVAC controller are grounded.
* Blower relay No. 1 and No. 2 are energized.
* Voltage is supplied to the blower motor through the following components:

- The closed contacts of the blower relay No. 1.
- The both sides of the blower motor resistor.
- CKT 65 (PPL).

The following conditions exist when the HVAC controller is in the medium (MED) position:

* Terminal L of the HVAC controller is not grounded.
* Blower relay No. 2 is de-energized.
* Voltage is supplied to the blower motor through the following components:

- The closed contacts of the blower relay No. 1.
- Only half of the blower motor resistor to CKT 63 (TAN).
- The open contacts of the blower relay No. 2.

The following conditions exist when the HVAC controller is in the high (HI) position:

* Terminal M of the HVAC controller is not grounded.
* Blower relay No. 2 is de-energized.
* Voltage is supplied to the blower motor through the following components:

- The open contacts of the blower relay No. 1.
- CKT 1649 (YEL).
- The closed contacts of the blower relay NO. 2 to the blower motor

The system voltage is supplied directly to the motor.