Troubleshooting
Here is a step by step guide to fixing your HVAC issue.
Each piece of equipment has an order of operation. Follow each list until you reach the step where your equipment is malfunctioning.
Condensing unit outdoor A/C unit
L1 & L2 wires are the 240v service power from the home coming out of the disconnect box. T1 & T2 wires are the 240v power going to the AC unit or heat pump. The 24v wires are coming from the indoor thermostat and signal the contactor close and bridge power from the constant home power service to the unit’s components allowing it to run
The order of operations for an A/C condensing unit is:
Thermostat signals the AC to come on when the temperature rises above the set point. ZZZHVACZXUF
The indoor furnace or air handler’s 24v low voltage control wiring signal is sent through the thermostat to the outdoor AC condenser’s contactor.
2)Thermostat is set to cool and low, the indoor fan comes on but not the outdoor AC
The contactor is an electrical component with a normally open circuit. When it receives the 24v signal from the thermostat it closes the circuit between the home’s main power supply and the compressor and fan motor. The 24v signal bridges the homes high voltage 240v power with the AC compressor and fan motor. When you walk up to an AC you can put your ear up to the unit and hear a buzz or hum if the contactor is engaged.
2)My indoor unit fan is running, thermostat is set low/cool, my AC has power to it, and the contactor is not engaged or not bridging power to unit
3)Outdoor AC unit fan comes on but not the compressor
4)Outdoor AC unit compressor comes on but the fan does not spin, hums loudly, or gets very hot.
5)The circuit breaker in my panel box or disconnect box trips each time I turn on the AC at the thermostat
Note: If you are unsure of how to replace the thermostat or do not feel comfortable working with electrical components, it's best to seek the help of a licensed HVAC technician to avoid any potential safety hazards. Contact a local HVAC contractor if you do not feel comfortable or do not have electrical experience.
Capacitors are another electrical component in an outdoor AC condenser or heat pump. They work by storing electrical energy in an electric field between two metal plates. When the capacitor is connected to an electrical source, an electrical charge is stored on the plates. When the capacitor is disconnected from the source, the stored charge is released and flows through the circuit, providing the energy needed to start the compressor and the fan motor. The top of a standard dual run capacitor has 3
he contactor closes: When the contactor receives the signal from the control board, it closes the circuit between the main power supply and the compressor and fan motor.
Electricity flows to the compressor and fan motor: With the circuit closed, electricity flows to the compressor and fan motor, allowing them to turn on and start running.
The contactor remains closed while the AC is running: As long as the AC is running, the contactor will remain closed, allowing electricity to flow to the compressor and fan motor.
The thermostat signals the AC to turn off: When the temperature in your home drops below the set temperature on your thermostat, it sends a signal to the AC to turn off.
An air conditioner capacitor is an electrical component that is used to store and release electrical energy in an air conditioning system. It works by storing electrical energy when the air conditioner is turned on and then releasing that energy to start the compressor and the fan motor.
Capacitors work by storing electrical energy in an electric field between two metal plates. When the capacitor is connected to an electrical source, an electrical charge is stored on the plates. When the capacitor is disconnected from the source, the stored charge is released and flows through the circuit, providing the energy needed to start the compressor and the fan motor.
Sensors: Various sensors, such as pressure and temperature sensors, monitor the system's performance and control the compressor and expansion valve.
Electrical components: The electrical components include wiring, relays, contactors and capacitors that control the operation of the compressor and fan motor.
All of these components work together to compress and circulate refrigerant through the system, removing heat from the indoor air and releasing it outdoors.
Heat Pump outdoor unit
A home heat pump is a type of heating and cooling system that works by transferring heat from one place to another using a refrigerant. It operates on the same principle as an air conditioner but can also provide heating by reversing the flow of the refrigerant.
During the cooling mode, the heat pump works similar to an air conditioner, removing heat from inside the house and transferring it outside. The process begins with the evaporator coil inside the home absorbing heat from the indoor air and transferring it to the refrigerant. The refrigerant then flows to the outdoor unit where it releases the heat to the outside air through the condenser coil.
In the heating mode, the heat pump reverses the refrigerant flow direction. The outdoor unit now functions as an evaporator coil, absorbing heat from the outside air and transferring it to the refrigerant. The refrigerant is then pumped to the indoor unit, where it releases the heat to warm the indoor air.
The heat pump cycle is driven by a compressor, which circulates the refrigerant between the indoor and outdoor units. The heat pump also has a reversing valve that controls the direction of refrigerant flow depending on whether heating or cooling is required. Heat pumps include the same parts as a normal condensing unit along with a reversing valve
Overall, a heat pump can be an efficient way to heat and cool a home, as it transfers heat rather than generating it, and can operate in a wide range of temperatures.
In a standard situation a heat pump is paired with an indoor electric air handler. A heat pump can be paired with a gas furnace in a dual fuel system.
Gas Furnace
The order of operation in a gas furnace can vary depending on the specific make and model, but here are the general steps: Note where in this ordered list your system stops or malfunctions.
Thermostat call for heat: When the thermostat detects that the temperature in the room has dropped below the set point, it sends a signal to the furnace control board. My unit never comes on in heat
Inducer motor (vent motor) start: The control board activates the inducer motor to start pulling air through the heat exchanger. My inducer vent motor comes on but is very noisy
Pressure switch activates: A small rubber tube pulls negative pressure from the inducer vent motor to the pressure switch, closing a circuit allowing the furnace to move on to the next step.
Ignition sequence: The control board sends a signal to the spark igniter or hot surface igniter to activate. The HSI hot surface igniter (most common) will glow orange for a few seconds. A spark ignitor will click and show a small spark to light the burners. The vent motor comes on but the ignitor never lights or sparks
Gas valve receives a signal from the control board to release gas and light the burners. The ignitor activates/lights but the burners never light
Flame sensor check: The furnace has a flame sensor that detects the presence of the flame. If the sensor doesn't detect a flame, it will shut off the gas valve to prevent a gas buildup. Burners light but only stay lit for 2-5 seconds and shut off
Blower motor start: Once the furnace detects that the burners have ignited, it will start the blower motor to circulate warm air throughout the house.
1)Burners light but after 30 seconds the blower motor never comes on.
2)Blower motor is very noisy or just hums.
3)Burners and blower motor run but shutoff prematurely before thermostat is satisfied.
Thermostat satisfaction: Once the temperature in the room reaches the set point, the thermostat will send a signal to the furnace control board to shut off the burners and blower motor.
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Electric Air Handler
An electric air handler is a component of an electric heating and cooling system that is responsible for circulating air throughout the home. It typically consists of an electric motor, fan, and filter.
When the thermostat signals for heating or cooling, the air handler's electric motor turns on, which activates the fan. The fan pulls air through the return ducts and passes it over the heating or cooling elements, depending on whether heating or cooling is required. The heating or cooling elements may include electric resistance heating coils or a refrigerant coil, respectively.
As the air passes over the heating or cooling elements, it is either heated or cooled and then blown through the supply ducts and into the home's living spaces. The air handler's filter helps to remove any contaminants, such as dust or pollen, from the air before it is circulated through the home.
Electric air handlers can be efficient and effective at heating and cooling homes, particularly in areas with mild climates. However, they may not be as energy-efficient as other types of heating and cooling systems, such as heat pumps or gas furnaces, in areas with very cold winters or very hot summers.
Evaporator Coil
An evaporator coil is a key component in an air conditioning system that is responsible for removing heat and humidity from the air. It is typically located inside the home, near the air handler or furnace.
The evaporator coil works by absorbing heat from the warm air that is blown over it by the air handler's fan. As the warm air passes over the cold surface of the evaporator coil, the heat energy is transferred from the air to the refrigerant inside the coil. The refrigerant then absorbs the heat and evaporates into a gas.
The now-cooled air is then blown back into the home, while the refrigerant gas is carried by the system's compressor to the condenser coil, located outside the home. There, the refrigerant is condensed back into a liquid state, releasing the heat that was absorbed by the evaporator coil into the outdoor air.
This cycle repeats as the air conditioning system continues to cool the home. The evaporator coil plays a crucial role in this process, as it is responsible for absorbing the heat from the air, making it cooler and more comfortable to breathe. In a gas furnace application the evaporator coil is a separate piece of equipment that attaches on top (upflow system) or the side (horizontal system) of the furnace. In an electric air handler application the evaporator coil is built inside of the unit.
However, if the evaporator coil becomes dirty or damaged, it can impair the efficiency and effectiveness of the air conditioning system, leading to higher energy bills and reduced comfort in the home. Regular maintenance and cleaning of the evaporator coil can help to ensure that the air conditioning system operates at peak performance.