Top 10 Gas Furnace Package Unit Problems!

Problem #1: No Power to the Package Unit

On all HVAC systems, power is critical to operation, and a package unit is no different. There several reasons a package unit may lose power, but fortunately determining if this is the problem can be done fairly simply.

First, remove the cover plate of the package unit to look at the control board. If the LED light on the control board is lit, there is power to the unit and the problem is something else. If the LED light is not lit, test for voltage at the contactor. If there is no voltage measured at the contactor, move to the electrical disconnect.

There are two types of electrical disconnects typically used on outdoor package units; fusible and non-fusible.

Before addressing the fuses or switch, it is good idea to test the line voltage (power coming into the disconnect from the building) to determine that power is present. If power is not coming into the disconnect then the electrical issue lies within the building, possibly at the indoor breaker and a licensed electrician should be consulted. However, if power is coming into the disconnect box, the issue is likely with the switch or fuses.

If the electrical disconnect uses a non-fusible disconnect switch, the switch may not be correctly connected in place, or it may be in the off position. If this is this case, resetting the switch to the proper position should restore power to the unit.

If the electrical disconnect uses a fusible disconnect switch, the fuses may be blown or bad. To determine if this is the case, check the resistance across each fuse individually to make sure that they are still intact. If the resistance measures 0.L. then the fuses are not inteact and need to be replaced, however, further testing may be necessary to determine why the fuse(s) failed.

Problem #2: Thermostat related issues

The thermostat is the device that is used by an individual to instruct the unit when and how to operate. Unfortunately, thermostats can fail over time or stop working due to damage to the thermostat wiring.

Before testing the thermostat itself, test the wires within the unit to make they are good. In order to determine the function of each color wire, read the units wiring diagram, which is usually found on the cover plate, to the control board.

Typically, the wires follow a pattern similar to the example below:

• Brown wire = Common from the transformer

• Red wire = 24 volt power from the transformer

• Green wire = for the fan

• Yellow wire = for air conditioning

• White wire = for heat

To test the wires in the unit, use a wire nut or jumpers to connect the power wire (red) and the heat wire (white). (Note: The thermostat wire and the thermostat batteries are bypassed when using a wire nut or jumpers to connect wires in the package unit.) When connected, the inducer motor should immediately turn on. If the inducer motor does not turn on, this indicates that the problem is likely with the thermostat or the thermostat wire.

The Thermostat Batteries

If testing the wires indicates that the

problem is within the thermostat or the thermostat wiring, the first thing to do is replace or test the thermostat batteries. If the charge in the batteries becomes low enough, the thermostat will not have the power to close the contacts to send a signal back to the control board in the unit.

the Thermostat Wiring

If the batteries are not the problem, it is likely that the thermostat wiring has been damaged. Since a portion of the thermostat wiring is outside, it is susceptible to damage from the elements and may even be chewed on by animals. It is important to thoroughly inspect the wiring, as it may need to be replaced.

Depending on how many individual wires are in the thermostat wire jacket, it may be possible to switch a damaged wire with a spare wire, if an extra wire is available. If this is done, be sure to switch the damaged wire with the spare both in the unit and at the thermostat.

If the previous steps did not correct the problem, be sure to test for the correct voltage between the hot and common wire. If the correct voltage is present from the transformer, then it is likely that the thermostat itself is damaged and needs to be replaced.

the Thermostat itself

If the wires, the batteries, and power to the package unit are not the issues, there is a chance that the problem is with the thermostat itself. In this case, replace the thermostat.

Problem #3: Seized Inducer Motor or the Inducer Motor Capacitor is Bad

The inducer motor, which is responsible for forcing the exhaust fumes out of the unit is a critical component to the heating process, but it can stop operating properly and prevent the system from running. To determine if the inducer has failed or has stopped working properly, first make sure that it has power. If the inducer motor has power, but the motor is not starting or moving, test the inducer motor capacitor. (Note: A shaded pole inducer motor does not have a capacitor.)

If the capacitor is not the issue, then test that the motor is not seized. With the power off, attempt to turn the motor shaft or fan blades of the inducer. If the shaft or blades will not turn or they are very stiff, the inducer motor will need to be replaced.

Problem #4: Damaged Inducer Wheel, Clogged Port, or a Pressure Switch Issue

Although the inducer motor itself may be functional, it is possible for problems to occur with the parts and components it is connected to.

Damaged Inducer Wheel

One issue that can prevent a functioning inducer motor from operating properly, is aa damaged inducer fan wheel or fan blades. To check, remove the inducer motor cover to see if the wheel is damaged. Replace any broken parts.

Clogged Port

The inducer is also connected to the pressure switch via small tubes. These tubes connect to ports on the inducer and pressure switch where pressurized air is moved. Unfortunately, these ports can become clogged over time. If a port appears to be clogged, it must be cleaned out. (Note: A piece of thermostat wire can be used to unclog the port.) Any small amounts of debris should easily be pushed out of the way.

Pressure Switch

Although less common, the pressure switch may be damaged or defective. If this is the case, it will need to be replaced.

Problem #5: Spark Ignition Wire

The spark ignition wire runs from the control board to the spark igniter. Typically the wire will run through a hole in a piece of metal to get from the control board compartment to the combustion compartment. The wire is usually protected by either plastic or rubber guards to prevent it from rubbing against the metal frame.

If the wire does rub against the metal frame and the insulation is removed, the metal wire may become exposed to the ground frame. Because of the high voltage used by the spark ignitor, the spark will jump from the exposed wire to the ground frame instead of traveling to the front of the burners where it is supposed to go. If this occurs, the wire needs to be replaced.

Problem #6: Spider Webs or Insects Clogging the Orifices or Burners

Another issue that tends to effect package units more than other types of systems are clogs in the orifices or burner due to insects or spider webs. One sign of clogging is that only some, but not ALL, of the burners light. This may lead to a system short cycling because the flame proving process cannot be complete.

In order to prevent insects from clogging them, it is important to regularly inspect and clean the burners and other orifices. Once clean, ensure the system starts and operates properly.

Problem #7: Rusted or Clogged Burner Tubes

Burner tubes can also become clogged or worn due to rust. In some cases the burners can become so rusted, that gas will not flow through the tubes or pass along the channel to the adjacent burner. Typically this problem is evident by one or more burners failing to fire.

With the power off remove the burner tubes and inspect for any rust or obvious obstructions. If the burner tubes appear to be salvageable, use a wire brush to clean the tube faces and the channels of any debris.

In some situations the burner tubes may be so rusted or deteriorated that they cannot be cleaned and reused. It is also possible for the channels to spread out or become so worn down that they prevent the flame from traveling to the adjacent burners. In this case, be sure to replace to burner tubes.

Problem #8: The Burners Shut off After Igniting

Several factors can cause the burners to shut off after igniting. These scenarios would involve a situation where all of the burners light and then the system shuts off. If any of the burners are not lighting, see the two previous problems. The most common cause for a system shutting off after igniting involves a failure in the flame proving process.

If the flame rod does not detect a flame in the burner it is monitoring, it will shut the burners shut off after a few seconds. It is also possible for the flame proofing process to fail if there is a bad ground to the package unit, or if the flame rod has carbon buildup on it.

If there is a build up of carbon on the flame rod, after turning the power off, clean the flame rod with steel wool. (Note: Remember, any time the package unit has power to it, there is voltage on the flame rod!)

When troubleshooting, be sure to check the status code light(s) on the control board for possible errors. Some causes for the burners shutting off after igniting are not as obvious. For example, another potential cause may be if the wind is blowing into the exhaust vent. In this case the wind will push back against the inducer motor, which may cause the pressure switch to trip and open up. When this happens the burners will shut off. To help prevent this issue, ensure that the exhaust vent is properly sealed and intact.

Problem #9: The Blower Motor does not Turn On

Often, if a blower motor does not turn on, the furnace will overheat and the high temperature limit will open, shutting off the system. Depending on the type of motor used by the blower, there may be a variety of causes. If the blower uses a PSC motor, the motor requires a capacitor to run. In this case, the capacitor should be tested and replaced if necessary. For more on capacitor testing, check out our video on "HVAC Blower Fan Motor CAPACITOR Quick Testing!" (Note: Even if a capacitor appears to be bad and is replaced, it may still be necessary to replace the blower motor itself, as it may have sustained damage from the faulty capacitor. Further testing may be required to know for sure.)

It is also possible for the PSC motor itself to be faulty. If the motor will not operate correctly, but the capacitor is in good condition, the motor may need to be replaced. However, prior to condemning the motor, be sure to properly test the motor to ensure it is the problem. For more on blower motor operation and testing, be sure to check out our "HVAC Blower Motor Class! PSC Motor Speeds, Colors, Ohms, Current, Shorts, Air Restrictions!" video.

Package units may also use ECM blower motors to operate. These motors do not use capacitors, however they have removable modules that can be inspected for damage. If a module appears to be damaged, the ECM motor will need to be replaced. For more on testing ECM motors, check out our video on "Fast Easy ECM FAN MOTOR Troubleshooting! ECM Blower Motors with Spade Terminals!"

Problem #10: Cracked Heat Exchanger

Heat exchangers in a package unit can deteriorate leading to cracks and holes in the heat exchanger tubing. A cracked heat exchanger can be a serious problem, as carbon monoxide may enter the building because of this. Often times, this kind of issue is indicated by a tripped flame rollout switch. If a cracked heat exchanger is suspected, steps should be taken to verify the condition of the heat exchanger. This can be done by first turning off the power and either using a scope or by manually accessing the heat exchanger compartment.

For safety reasons, it is imperative that a cracked heat exchanger be replaced in a timely manner.

Some Airflow Tips

• If the supply duct rots and return duct are exposed to the elements, one or both may rot out, resulting in the unit working inefficiently.

• If the supply duct rots, it may result in air being blown outside the building.

• If the return duct rots, it may result in outside air being sucked into the system.

• A special shroud may need to be constructed around the ductwork to protect it from the elements.

• An opening may develop where the ductwork enters the building. This opening may allow an animal access to the crawl space where it can enter the building and damage the flex ducts (ripping into them and causing them to collapse), or other parts of the unit.

• The filters on package units are usually located inside the building. They need to be replaced regularly to get the proper airflow across the heat exchanger.

Looking for some hands on examples of troubleshooting? Check out our "NO HEAT?Top 10 Problems on a Gas Furnace Package Unit!" video below!

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Published: 11/1/2023 Author: Craig Migliaccio

About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 15 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at https://www.acservicetech.com & https://www.youtube.com/acservicetechchannel