Theory and operation
Heat pumps can reverse or reroute refrigerant through multiple valves; electric heaters may supplement output at low temperature or during faults.
Thermal Systems / Diagnostic guide
HEAT-PUMP DIAGNOSTICS.
Interpret reversible refrigerant flow and its interaction with battery and cabin thermal demands.
EV GUIDE18/24
Use this guide to organize evidence. Vehicle-specific high-voltage access, measurements and component isolation require OEM procedures, appropriate qualifications, rated PPE and approved test equipment.
GUIDE PURPOSE
Diagnose the system—not one isolated value.
Confirm vehicle state, operating conditions and the full DTC record before clearing evidence or opening the high-voltage system.
Diagnostic evidence
Compare ambient/cabin targets, compressor speed, high/low pressure, valve commands, coolant temperatures and heater contribution.
Safe diagnostic path
Identify the commanded operating mode, then verify pressure and temperature changes across the components used in that mode.
Boundary and common error
Generic pressure charts are insufficient for variable-speed, multi-evaporator EV heat-pump systems.
Specifications, connector access, disable sequences, wait times and allowable tests vary by model and voltage architecture.