Wiktor Wise
An electric furnace sequencer is a device that turns on or off one or more heating elements in a staggered fashion. This is necessary to limit the electric current spike that occurs when an electrical device is energised. If all the elements in a unit were energised at the same time, the current surge would probably cause the breaker to trip or the fuse to blow. If you suspect that a sequencer is bad, you should test it before replacing it. To do this, you should begin by shutting off the power to the furnace and verifying that it is off with an electric test meter. Then, you should disconnect the wires from the coil terminals and measure the resistance of the coil. A simple circuit test using a multimeter will let you determine in less than a minute whether the part is broken.
| Characteristics | Values |
|---|---|
| Purpose | Turns one or more heating elements on and off |
| Function | Staggering the heating elements so they turn on one at a time, in "sequence" |
| Testing | Begin by shutting off the power to the furnace and verifying that it is off with an electric test meter |
| Testing | Disconnect the wires from the coil terminals and measure the resistance of the coil |
| Testing | Adjust the multimeter to test for continuity |
| Testing | Touch the two probes on the meter against each pair of screw terminals on the sequencer, one pair at a time |
| Testing | If the multimeter registers zero or the display numbers roll to infinity, the set of terminals is defective |
| Testing | If the reading is zero or considerably higher than 20 ohms, replace the sequencer |
| Replacement | Obtain an exact replacement if possible |
| Replacement | If there is no part number, match the heater voltage, the length of on/off timings, and the number of switches |
| Installation | Mount the switch and reconnect the wires |
| Installation | Turn the power back on to the unit and observe a complete heating cycle to verify proper unit operation |
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What You'll Learn
Shut off the power to the furnace and verify with a meter
Shutting off the power to the furnace is the first step in testing an electric furnace sequencer. This is a necessary safety precaution to prevent any accidents or injuries. Once the power is shut off, it is important to verify that it is indeed off before proceeding with any repairs or maintenance. This can be done using an electric test meter.
To begin, locate the power source for the furnace and turn it off. This could be a simple switch or a breaker in your electrical panel. If you are unsure where the power source is located, refer to the furnace's documentation or consult a qualified technician. It is important to note that working with electrical systems can be dangerous, and it is always recommended to seek professional assistance if you are uncomfortable or unfamiliar with the process.
After shutting off the power, allow some time for the system to cool down, as electric furnaces can become very hot during operation. Once cooled, approach the furnace and verify that the power is indeed off using an electric test meter. Ensure that the test meter is appropriately rated for your electrical system's voltage and current.
Connect the test meter to the furnace's power supply according to the meter's instructions. Different meters may have different connection methods, so refer to the meter's manual for specific instructions. Once connected, observe the meter's reading. It should indicate that there is no power flowing to the furnace. If the meter shows any power flow, re-check that you have correctly identified and shut off the power source.
If the test meter confirms that the power is off, you can proceed with further testing or maintenance on the electric furnace sequencer. Remember to exercise caution and follow proper safety procedures throughout the process.
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Disconnect wires from coil terminals
Before disconnecting the wires from the coil terminals, it is important to shut off the power to the furnace and verify that it is off using an electric test meter. This is a crucial safety step to prevent any accidents or damage to the furnace.
Once the power is off, you can begin disconnecting the wires. It is recommended to start with the wires at the bottom and work your way up. Label each wire and its corresponding terminal before removal to make it easier to reconnect them correctly later. The wires are usually connected to the terminals via mounting screws, so simply loosen or remove the screws to detach the wires.
If your furnace has multiple heating coils, you may need to identify which wires correspond to each coil. This is important because disconnecting the wrong wires could affect the functioning of the coils. Each coil has its own sequencer, and the control wires from the board are tied together. The coils are typically connected in parallel, and by disconnecting the wires from one coil, you can effectively disable it while keeping the other coil operational.
When disconnecting the wires, be cautious of any loose wires that may be dangling inside the unit. It is important to handle this step carefully to avoid any short circuits or unintended connections. Ensure that all wires are securely disconnected from their respective coil terminals before proceeding to the next step of testing the electric furnace sequencer.
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Measure coil resistance
If you suspect that your electric furnace sequencer is faulty, you should test it before replacing it. To do this, you must first shut off the power to the furnace and verify that it is off using an electric test meter. Once you've done that, disconnect the wires from the coil terminals.
Now you can measure the coil resistance. A typical reading for coil resistance should be around 20 ohms. If the reading is zero or considerably higher than 20, you should replace the electric furnace sequencer.
The heat relay in an electric furnace consists of a heater coil, a bimetal switch, and connections for wires. The heater coil on modern units is powered by 24 volts from the furnace control board. On older units, some of the coils were powered by 120 or 240 volts. When power is supplied to the heater coil, an electric current flows and produces heat in the relay.
If your coil resistance reading is within the normal range, you can reconnect the wires and turn the power back on to the unit. To complete your electric furnace sequencer replacement, you should observe a complete heating cycle to verify proper unit operation.
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Observe complete heating cycle
To observe a complete heating cycle, you must first install a new relay by mounting the switch and reconnecting the wires. Then, turn the power back on to the unit.
The sequencer is a critical component of an electric furnace. It regulates the heating elements, ensuring they don't all turn on at the same time, which could overload the electrical system and trip the circuit breaker. Voltage enters the sequencer and is directed to the first heating element. Once this element reaches a set temperature, the sequencer allows voltage to flow to the next element, and so on.
If your sequencer is malfunctioning, you may notice that your furnace isn't heating your home effectively. The sequencer may be not allowing the furnace to turn on all its heating elements, or it may be faulty, causing the elements to activate simultaneously and trip the breaker.
To test your sequencer, shut down the furnace at the main breaker and verify it's off with an electric test. Disconnect the wires from the sequencer and use a multimeter to check the voltage. A reading of around 24V indicates a functioning sequencer, while a reading of zero or a low voltage suggests the need for a replacement.
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Check the thermostat
If your electric furnace won't start up, the first place to look for the source of the problem is your thermostat. Even the highest-quality models eventually wear out. Some common signs that your thermostat is malfunctioning include:
- The furnace or air conditioner won't turn on.
- There is no change in your home's temperature after adjusting the temperature setting, or the setting and temperature don't match.
- The HVAC is running continually without stopping.
- The thermostat has no power.
Before calling your local HVAC professionals for assistance, there are some troubleshooting tips you can try. Firstly, check the thermostat programming. If setting the temperature manually makes your furnace come on, but your system doesn't turn on and off according to your programming, check to be sure the program has not been reset to its default mode due to a power outage. You can find the manual online by searching with the model number.
Secondly, check the batteries. Most programmable thermostats are battery-operated, so the first thing to do if your furnace will not come on is to change the batteries. Replace the batteries of a battery-powered thermostat with new ones to ensure that this is not the source of the problem. Typically, you will need to replace the batteries on a yearly basis. If you have an older manual mercury-switch thermostat, it may be hardwired into your heating system without any batteries.
Thirdly, check the thermostat setting. Ensure your thermostat is set to "heat" before you try to get your furnace to come on. Set your thermostat temperature at least five degrees above room temperature, so your thermostat can call for heat from the furnace.
Finally, if you are comfortable working with electrical devices, you can try a bypass test. Remove the wiring from the back of your thermostat and close the circuit by twisting the hot and ground wires together. If your furnace comes on when you do this, it’s a good indication that your thermostat has failed and should be replaced.
If none of these tips work, you may be experiencing a wiring issue that requires professional repair. Knowing how to check thermostat wires for power is crucial. The easiest way to test a thermostat that does not require powering down your unit or disconnecting wires involves using a multimeter. A multimeter is a simple electronic device that uses a dial to measure power voltage within an electrical system. Begin by removing the thermostat cover and, if necessary, the sensor plate to access the wires. Once you’ve accessed the unit’s wires, set your meter dial to an appropriate dial setting. This setting depends on your thermostat’s voltage; if you have a 24 V thermostat, for instance, set your meter within that range. Place the multimeter’s red probe onto the thermostat terminal marked R for red, and place the black probe onto any of the other terminals.
It is important to note that you should only attempt to perform electrical work if you feel confident in doing so. If you are unsure, it is always best to call a professional for assistance.
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Frequently asked questions
If your furnace is not heating normally, or if some elements are glowing orange but others are not, the sequencer may be defective. You can test this using a multimeter or an electric test meter.
First, shut off the power to the furnace and verify it is off with an electric test meter. Then, disconnect the wires from the coil terminals and measure the resistance of the coil. If the reading is zero or higher than 20 ohms, you should replace the sequencer.
First, label and disconnect the wires from the old unit. Then, remove the mounting screw to take out the old unit. To install the new unit, simply mount the switch and reconnect the wires. Turn the power back on and observe a complete heating cycle to verify proper operation.
