Air Conditioning

A/C System Tests (cont'd)

 21-100  

Pressure Test

Test results Related symptoms Probable cause Remedy
Discharge (high) pressure abnormally high After stopping compressor, pressure drops to about 196 kPa (2.0 kgf/cm{sup 2}, 28 psi) quickly and then falls gradually. Air in system Discharge, evacuate (see page 21-94) and recharge with specified amount (see page 21-96).
No bubbles in sight glass when condenser is cooled by water Excessive refrigerant in system Discharge, evacuate and recharge with specified amount.
Reduced or no air flow through condenser
  • Clogged condenser or radiator fins
  • Condenser or radiator fan not working properly
  • Clean
  • Check voltage and fan rpm.
  • Check fan direction.
Line to condenser is excessively hot. Restricted flow of refrigerant in system Restricted lines
Discharge pressure abnormally low Excessive bubbles in sight glass; condenser is not hot. Insufficient refrigerant in system
  • Check for leak.
  • Charge system.
High and low pressures are balanced soon after stopping compressor. Low side is higher than normal.
  • Faulty compressor discharge valve
  • Faulty compressor seal
 Replace the compressor.
Outlet of expansion valve is not frosted, low-pressure gauge indicates vacuum.
  • Faulty expansion valve
  • Moisture in system
  • Replace
  • Discharge, evacuate and recharge with specified amount.
Suction (low) pressure abnormally low Excessive bubbles in sight glass; condenser is not hot. Insufficient refrigerant in system
  • Repair the leaks.
  • Discharge, evacuate and recharge with specified amount.
  • Charge as required.
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
  • Discharge, evacuate and recharge with specified amount.
  • Replace the expansion valve.
Discharge temperature is low and the air flow from vents is restricted. Frozen evaporator Run the fan with 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 check joint are cooler than the temperature around evaporator. Expansion valve open too long Repair or replace.
Suction pressure is lowered when condenser is cooled by water. Excessive refrigerant in system Discharge, evacuate and recharge with specified amount.
High and low-pressure are equalised as soon as the compressor is stopped and both gauges fluctuate while running.
  • Faulty gasket
  • Faulty high-pressure valve
  • Foreign particle stuck in high-pressure valve
 Replace the compressor.
Suction and discharge pressures abnormally high Reduced air flow through condenser.
  • Clogged condenser or radiator fins
  • Condenser or radiator fan not working properly
  • Clean
  • Check voltage and fan rpm.
  • Check fan direction.
No bubbles in sight glass when condenser is cooled by water Excessive refrigerant in system Discharge, evacuate and recharge with specified amount.
Suction and discharge pressure abnormally low Low-pressure hose and metal end areas 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 Compressor clutch is dirty. Compressor shaft seal leaking Replace the compressor.
Compressor bolt(s) are dirty. Leaking around bolt(s) Tighten bolt(s) or replace compressor.
Compressor gasket is wet with oil. Gasket leaking Replace the compressor.