A/C System Test
Pressure Test
Test results
Related symptoms
Probable cause
Remedy
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 id dirty.
Leaking O-ring
Clean the A/C fitting and replace the O-ring.