Hvac Trouble Shooting Chart

 Like any other electrical device an HVAC is also a contraption. It is subject to wear and tear and therefore malfunctions. Here we will discuss some commonly found malfunction in HVAC units and their probable causes:


The heat pump never reaches desirable temperature

In a chilly climate you may have set your thermostat at 75 degrees to make your rooms warm and comfortable. But you seem to be getting only 65 degrees of heat. It is a problem and a genuine problem too. You should know that heat pump is not efficient in extreme weathers. The pump is not able to source heat from the cold atmosphere to make your house warm. However,some heat pumps are integrated with as supplemental heating element which comes to its assistance in such situation.

 There could be an array of reasons for a heat pump not producing enough heat. Let’s look into them one by one:

• Faulty and not-calibrated thermostat
• The level of refrigerant is low
• Refrigerant is not flowing well
• Problems in the reversing valve or compressor valves
• Faulty compressor
• Frozen outdoor uni tor the external unit trapped in a mass of snow
• Not working outdoor unit
• Leakage in ducts or bad insulation
• A short circuit or tripped breaker in supplemental heating nit.

 Problem #2

Compressor is running non-stop.

If your HVAC seems is running without a break, then this could indicate a problem. This will result in high utility bills, lower supply temperatures, and sometimes icing of the outdoor unit. There could be a gamut of reasons for constantly running compressor. Here is a list of them:

• This could be due to overload
• Running in A/C mode
• Low Freon Level
• The suction pressure has gone down due to some obstruction in liquid line.
• Expansion valve is no working flexibly

 • The evaporator and the condenser has not been cleaned for a long time
• The fan motor of the indoor unit is not working
• Filters have not been changed for long
• Poor insulation and defrost heater is on constant operation
• Problems in low pressure control, temperature control, hot gas bypass valve or capacity control valve.
• The suction line to the liquid line heat exchange has been damaged.
• The evaporator pressure regulator valve is not functioning properly
• Leaking valves
• The defrost system should be looked into
• Undersized unit


The Compressor starts but goes off on overload protector system.

The reasons for this are many. Here is quick glance at them.
• This could be due to high suction pressure. Check respective documents for maximum suction pressure of the compressor. You will need a Crankcase Pressure Regulator (CPR) or pressure limited TXV (MOP) to measure the pressure.
• The discharge pressure is extremely high
• The supply voltage is too low
• Lose connections and wiring
• Faulty capacitor, overloads protector, start relay
• Short circuit in the motor winnings or it has got earthed
• Faulty compressor or the bearing of the compressor is too tight

Compressor cycles off frequently

This generally happens when the unit is oversize. This can lead to other problems like the machine will wear and tear very fast. It will remove too much humidity which will render a damp and uncomfortable feeling in the rooms. However there are other reasons for frequent cycling off. They are:

The difference in pressure and temperature control is too less
• Refrigerant level has gone too low
• The pressure discharge is too high
• The condenser unit is too dirty
• There is surfeit refrigerant on non-receiver system.

 • Compressor valve is leaking
• High suction pressure
• Voltage fluctuation
• Poor air flow through the evaporator
• Improper flow of refrigerant
• In off cycles there are instances of leakage in the liquid line solenoid valve
• Partial load, low humidity, etc, without capacity control.
• The receiver is not insulated


Compressor does not start. It only makes humming sound.

The probable reasons for this could be:

• Faulty wiring
• Low voltage
• Problem in the run or start capacitor
• Faulty start relay
• Uneven pressure on PSC moto
• Short circuit in the motor windings or it has got earthed
• Compressor is damaged or its bearings are too tight


HVAC is really blowing cold air in summer

This means that your HVAC is not delivering any heat at all. This can be acaused by several things.Only its air condition mode is functioning due to somefaults inside. The reasons could be:

• The refrigerant level has dipped down
• Restriction in the flow of refrigerant
• Unit is in need of cleaning and servicing
• Problems in reversing valve and compressor valves
• Working in A/C mode
• The outdoor unit is frozen due to faults or weather
• Outdoor unit not running
• Thermostat is set too low
• The air handler in the attic with return trunk has become disconnected from the unit

Besides the problems already stated there could be some other issues that are seen very commonly in household units. One such problem is air condenser isn't running. In such a case always check if the unit is plugged on. Also check for blown fuse or tripped breaker. Also check if the thermostat is set at correct temperature.

Sometimes you may feel that the HVAC is not cooling sufficiently. Lower the thermostat in sucha case. If it does not fix the problem, give theevaporator a thoroughcleaning. If itdoes notbring a result, calla technician. The problem can also occurdue to improperly sized unit.

If the AC is running but not cooling at all, then the condenserunitcould be cluttered with weeds, leaves and debris. Give it agood cleaning. Also check the thermostat. If these things are fine then you need a professional repair.