A/C System Test
Pressure Test
Test results
Related symptoms
Probable cause
Remedy
Driver's and passenger's side vent temperatures vary by more than 11 °C (20 °F)
Poor A/C performance. Discharge (high) and suction (low) pressures are low.
Low refrigerant charge
Recover, evacuate, and recharge with specified amount.
Air mix door inoperable
Repair or replace.
Discharge (high) pressure abnormally high
After stopping A/C compressor, pressure drops about 196 kPa (2.0 kgf/cm 2 , 28 psi) quickly, and then falls gradually.
Air in system
Recover, evacuate, and recharge with specified amount.
Reduced or no airflow through A/C condenser.
  • Clogged condenser or radiator fins
  • A/C condenser or radiator fan not working properly
  • Clean.
  • Check voltage and fan rpm.
  • Check fan direction.
Line to A/C condenser is excessively hot.
Restricted flow of refrigerant in system
Restricted lines.
Discharge pressure abnormally low
High and low-pressures are balanced soon after stopping A/C compressor. Low side is higher than normal.
  • Faulty A/C compressor discharge valve
  • Faulty A/C compressor seal
Replace the A/C compressor.
Outlet of expansion valve is not frosted, low-pressure gauge indicates vacuum.
  • Faulty expansion valve
  • Moisture in system
  • Replace.
  • Recover, evacuate, and recharge with specified amount.
Suction (low) pressure abnormally low
Expansion valve is not frosted, and low-pressure line is not cold. Low-pressure gauge indicates vacuum.
  • Frozen expansion valve (Moisture in system)
  • Faulty expansion valve
  • Recover, evacuate, and recharge with specified amount.
  • Replace the expansion valve.
Discharge temperature is low, and the airflow from vents is restricted.
Frozen evaporator
Run the fan with A/C compressor off, then check evaporator temperature sensor .
Expansion valve is frosted.
Clogged expansion valve
Clean or replace.
Receiver/dryer outlet is cool, and inlet is warm (should be warm during operation).
Clogged receiver/dryer
Replace.
Suction pressure abnormally high
Low-pressure hose and service port are cooler than the temperature around evaporator.
Expansion valve open too long
Repair or replace.
Suction pressure is lowered when A/C condenser is cooled by water.
Excessive refrigerant in system
Recover, evacuate, and recharge with specified amount.
High and low-pressures are equalized as soon as the A/C compressor is stopped, and both gauges fluctuate while running.
  • Faulty gasket
  • Faulty high-pressure valve
  • Foreign particle stuck in high-pressure valve
Replace the A/C compressor.
Suction and discharge pressures abnormally high
Reduced airflow through A/C condenser.
  • Clogged A/C condenser or radiator fins
  • A/C condenser or radiator fan not working properly
  • Clean.
  • Check voltage and fan rpm.
  • Check fan direction.
Suction and discharge pressures abnormally low
Low-pressure hose and metal fittings are cooler than evaporator.
Clogged or kinked low-pressure hose parts
Repair or replace.
Temperature around expansion valve is too low compared with that around receiver/dryer.
Clogged high-pressure line
Repair or replace.
Refrigerant leaks
A/C compressor clutch is dirty.
A/C compressor shaft seal leaking
Replace the A/C compressor.
A/C compressor bolt(s) are dirty.
Leaking around bolt(s)
Tighten bolt(s) or replace A/C compressor.
A/C compressor gasket is wet with oil.
Gasket leaking
Replace the A/C compressor.
A/C fitting is dirty.
Leaking O-ring
Clean the A/C fitting and replace the O-ring.