Expansion Valve: Testing and Inspection

Checking expansion valve operation

Check

1. Connect service hose or pressure gauge at low pressure side (discharge) of air conditioner.
2. Remove knee guard underneath glove compartment.

3. Start engine and adjust it to a speed of about 2000 RPM. Turn air conditioner on, switch fan to maximum speed and open car doors.

4. After waiting several minutes, measure discharge temperature at evaporator with a thermometer suitable for measuring surface temperature. Take pressure reading at same time. It is important that the compressor runs (clutch applied) while making measurements.

Pressure - Temperature Relationship For Refrigerant R-12:

5. Read temperature from graph. It must be about 10 to 12°C (18 to 20°F) lower then the discharge temperature measured at the evaporator.

Example:
Pressure gauge reading: 1.6 bar (25 psi)
Corresponding temperature from graph: approx. - 6°C (21°F)
Temperature measured at evaporator outlet: approx. + 5°C (41°F)
The difference in temperature between - 6°C (21°F) and + 5°C (41°F) is 11°C (2O°F); consequently the expansion valve adjustment is correct. Expansion valve would have to be replaced, if the difference in temperature would be less than 5°C (9°F) or more than 17°C (41°F).