Positive Temperature Coefficient Heater: Echo
Positive Temperature Coefficient (PTC) heater is a small electrical heater located in the heater core and is used on vehicles equipped for cold areas. See Fig 1. PTC heater may be turned on if all of the following conditions exist: temperature control switch is at MAX HOT position, engine speed is more than 1050 RPM, engine coolant temperature is less than 176°F (80°C) and generator power ratio is less than 95 percent. PTC heater may also be turned on and off depending on generator power ratio.
Temperature control switch operates a maximum hot switch, which provides an input signal to Engine Control Module (ECM) for controlling PTC heater operation. Maximum hot switch may also be referred to as MAX HOT switch.
HTR SUB1 relay is used for supplying battery voltage to PTC heater. HTR SUB1 relay may also be referred to as heater sub relay. HTR SUB1 fuse supplies battery voltage to one side of HTR SUB1 relay. When ignition is turned on, voltage is supplied from ignition switch, through ECU-IG fuse and to other side of HTR SUB1 relay. When PTC amplifier completes ground circuit for HTR SUB1 relay, HTR SUB1 relay then provides battery voltage to PTC heater for PTC heater operation. HTR SUB1 relay is located in fuse/relay box at driver's side front corner of engine compartment, just in front of strut tower.