Principles of Operation

Seats

Principles of Operation - Heated Seats


Heated Seats

The HVAC module contains the heated seat control buttons and indicators. The heated seat system operates independently from the climate control system and the engine must be running.

A heated seat relay is located underneath each heated seat cushion frame. There are 2 voltage supplies to the heated seat relay. Voltage is supplied from the Smart Junction Box (SJB) to each heated seat relay coil when the ignition is ON. The HVAC module supplies ground to a relay coil when a heated seat switch button is pressed to energize the relay. This closes the relay contact to supply battery voltage from the SJB to the cushion heater mat. The cushion and backrest heater mats are wired in series and the backrest heater mats are directly connected to ground to complete the electrical circuit to heat a seat.

Each cushion heater mat contains a non-serviceable internal thermostatic switch that closes when cold to complete the heater grid circuit and heat the seat. When hot, the thermostatic switch opens the heater grid circuit and allows the seat to cool. During normal operation, several minutes may be required before seat temperature is increased and several more minutes of cooling before the heater mats continue with heating. The heated seat indicator illuminates continuously while the thermostatic switch cycles open and close.

The seat should be occupied to correctly test for normal operation. Temperature measuring devices do not provide an accurate method for testing heated seat operation as surface temperatures are subject to human and environmental characteristics. Correct testing requires heater mat resistance measurements which have tight tolerances affecting heat cycle time length.

The heated seat system does not time-out. A heated seat will remain on until the heated seat switch or ignition is switched OFF.