HVAC Basic Troubleshooting

Frost build-up on evaporator coils

  • Lack of airflow, dirty filters, dirty coils.

Low suction in the condenser

  • Low refrigerant charge or leaks.
  • Blocked expansion valve (moisture, dirt, etc).
  • Reduction of flow in evaporator.

Leak detection

  • Ultraviolet dye.
  • Soap bubbles.
  • Electronic detectors.
  • First check all fittings and coils. If leak cannot be found, system must be reclaimed and pressure tested.

Signs of leaking Freon

  • Warm air supply and low airflow.
  • Increase in electricity bills.
  • Bubbling or gurgling noises.
  • Refrigerant poisoning.

Low suction pressure

  • Insufficient heat getting to the evaporator caused by low airflow (dirty filter, slipping belt, restricted ductwork). Check for proper superheat.
  • Defective, plugged, or undersized metering device. superheat doesn’t change, and the subcooling increases. Check sight glass. Obstructions in filter/dryer.
  • Low refrigerant. Superheat is high and the subcooling is low.
  • Check superheat and subcooling to make the correct diagnosis.
  • Superheat indicates how much refrigerant is in the evaporator (high superheat indicates not enough, low superheat indicates too much).
  • Subcooling gives an indication of how much refrigerant is in the condenser.

How to Measure Superheat

  1. Take pipe temperature at the suction line using a contact thermocouple (don’t use IR).
  2. Convert suction pressure to temperature.
  3. Subtract the two numbers.

How to Measure Supercooling

  1. Attach a thermometer to the liquid line near the condenser.
  2. Take the head pressure and convert it to temperature.
  3. Subtract the two numbers.

Surging in Chiller Compressors

  • Surging is caused by increased condenser pressure, problem with cooling tower or water in between (blockage).
  • Occurs when pressure in the condenser is too great and starts to push back into the evaporators.
  • Can cause very serious damage.
  • Chiller will make very loud “groan” from compressor. Sound will suddenly stop when pressure equalizes. Also causes fluctuation in compressor motor current.
  • Change in flow rate, drop below minimum.
  • Pump strainer blockage.
  • Cooling tower unable to reject enough heat: Motor, drive belt, water distribution (leaves, flow blockage), etc.
  • Fouling in condenser.