System components
This component acts as the "pump" of the AC system, compressing low-pressure vapor into high-pressure vapor.
The Compressor
If a vehicle's AC system is completely empty of refrigerant due to a major leak, what will both the high and low-side gauges read when the vehicle is off?
0 PSI (Atmospheric pressure)
If the cabin blower motor works perfectly on High speed but does not work at all on speeds 1, 2, or 3, what specific component has failed?
Blower Motor Resistor
A customer states their AC blows cold on the highway, but turns warm when idling at a red light. What is the first component you should visually inspect for operation?
The Condenser Cooling Fan
Because electric vehicles lack a running internal combustion engine to turn a traditional belt, what type of motor is integrated directly inside an EV's AC compressor?
A high-voltage electric motor (usually a 3-phase brushless DC or AC synchronous motor)
Located right in front of the engine radiator, this component changes hot, high-pressure refrigerant gas into a high-pressure liquid.
The Condenser
When testing a normally operating system on an 85°F day, the low-side gauge should typically read within this general PSI range. (Allow a 10 PSI window).
20 to 35 PSI (Accept anywhere within 15–40 PSI, depending on refrigerant type)
This safety switch is wired into the compressor control circuit to shut the system down if refrigerant pressure drops too low or spikes dangerously high.
Pressure Switch (or High/Low Pressure Transducer)
You find a heavy layer of oily dirt caked around a single aluminum line fitting under the hood. What does this visual clue indicate?
A refrigerant leak (refrigerant oil escapes with the gas and traps dirt)
Traditional PAG oil conducts electricity. What specific type of high-dielectric oil must be used in EV electric compressors to prevent high-voltage isolation faults?
POE Oil (Polyolester) or specialized non-conductive EV-spec PAG oil
This restricted metering device sits right before the evaporator and drops the pressure of the liquid refrigerant.
Thermostatic Expansion Valve (TXV) or Orifice Tube
If your gauges read 30 PSI on the low side and 350+ PSI on the high side, what is the most likely cause?
Failed condenser cooling fan or severely blocked condenser airflow
If the driver-side vents blow ice cold but the passenger-side vents blow hot air on a dual-zone climate system, what electronic dashboard actuator is likely jammed or broken?
Blend Door Actuator (or Temperature Door Actuator)
An AC system blows ice cold for the first 10 minutes of a drive, but then gradually slows its airflow to a whisper and stops cooling. After sitting turned off for 20 minutes, it works fine again. What is happening inside the dash?
The evaporator core is freezing over
Many EVs use the AC system not just to cool the cabin, but to actively chill or warm this massive, temperature-sensitive vehicle component. What is it?
The High-Voltage Hybrid/EV Traction Battery Pack
Found on the low-pressure side of systems using an orifice tube, this canister prevents liquid refrigerant from reaching and slugging the compressor.
The Accumulator
When a compressor's internal valves fail or the compressor wears out completely, what happens to the low-side and high-side gauge readings while the engine is running?
The pressures equalize / low-side stays high and high-side stays low (Gauges "meet in the middle")
When checking the control signal of an electronically controlled compressor valve with a digital storage oscilloscope, what type of modulated waveform pattern are you looking for?
Pulse-Width Modulation (PWM) duty cycle wave
If an HVAC case drain line gets plugged with debris, what symptom will the driver or passenger notice?
Water/condensation leaking onto the carpet
Instead of using a standard electric resistance heater that drains the battery quickly in cold weather, many modern EVs use a system that reverses the AC process to pull ambient heat from the outside air. What is this system called?
A Heat Pump System
On a modern variable-displacement compressor, this internal or electronically pulse-width modulated component alters the compressor's stroke instead of cycling a clutch on and off.
The Control Valve (or Solenoid Control Valve)
A restricted expansion valve (stuck closed) will cause the high-side pressure to be normal to low, but what distinct extreme reaction will you see on the low-side gauge?
It will drop into a vacuum (below 0 PSI)
An HVAC control unit sets a fault code for an open circuit on the "evaporator temperature sensor." Why does the computer intentionally disable the compressor clutch when this code is active?
To prevent the evaporator core from freezing into a block of ice
A technician hooks up a recovery machine and finds a system is full of refrigerant, but the scan tool shows the HVAC module is reading a 0 PSI system pressure. What is the next logical component to test?
The AC Pressure Sensor/Transducer circuit (wiring or sensor failure)
In an EV cooling system circuit, what electronic component acts like an automated faucet, using a stepper motor to precisely route refrigerant toward either the cabin evaporator or the battery chiller?
An Electronic Expansion Valve (EXV) or Chiller Control Valve