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Electric Furnace Problems (Please Read)

Electric Furnace Problems

Every year we field 1000's of tech calls for electric furnace not working properly or my fan quit working and my heater blows only cool or luke warm air. 

The MAIN BRAIN to your electric furnace is the sequencer! replacement sequencer 2 timings 4 switches H1-110 C1-110 01-0843It controls when to bring on the electric heat elements in sequence along with controlling the blower motor in the heating mode. 

Click to watch how a sequencer works ---> https://youtu.be/5YjL8eR5VJ0

With this electric furnace sequencer replacement guide, you will be able to diagnose, select a suitable replacement, and replace a faulty electric heat relay / sequencer / contactor


An electric furnace sequencer is a device that turns one or more heating elements on and off. This is necessary to limit the electric current spike that occurs when an electrical device is energized. If all the elements in a unit were energized at the same time, the current surge would probably cause the breaker to trip or the fuse to blow. If all the elements in a unit were energized at the same time, the current surge would probably cause the breaker to trip or the fuse to blow.

Normal Operation

In order to tell whether a part is broken or not, we must know how it normally works. The heat relay 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 volt power. When power is supplied to the heater coil, electric current flows and produces heat in the relay. This heat causes a small piece of metal in the bimetal switch to deform and close the contacts of the switch. When the contacts close, power is supplied to the electric elements. When the power to the heater coil is interrupted, the small piece of metal cools off and goes back to it's original shape. This causes the contacts to open and interrupts power to the elements.

Testing A Sequencer

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. This will normally be around 20 ohms. If the reading is zero or considerably higher than 20, you should continue with electric furnace sequencer replacement.

Electric Furnace Sequencer Replacement

To select a replacement, you should obtain an exact replacement if possible. The relay will have a manufacturer's part number on it. If there is not a part number on it, you should match the heater voltage, the length of on/off timings, and the number of switches. The on timing will normally look something like H1-20 which means that the switch will close between 1 and 20 seconds after power is applied to the heater. The off timing will usually look similar to C40-110 which means that the switch will open between 40 and 110 seconds after power is removed from the heater coil. To remove the old unit, start by labeling all of the wires that are connected to it and where they are connected. (take your cell phone and take pictures) Then, removal is usually accomplished by removing a mounting screw. To install the new relay, you simply mount the switch and reconnect the wires. Then, you can 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.

If you need help or a wire diagram Don’t Panic! Just send us an email colemanhvacparts@gmail.com and we can look up a wire diagram for most models.

Click HERE for a full HVAC guide 

Sequencer Cross Reference Chart

by Packard

HS33247  SPDT HEAT SEQUENCER, 1 TIMING, 1 SWITCH (1 element or 3KW - 5KW)

Carrier                       HN67GJ002

Diversitech                DGS108

Gemline                     GS108

Goodman                  B1370738

ICP                             HN67GJ002

Janitrol                       B1370738

Klixon                        60000COM-21

Klixon                        COM-21

Mars                           33247

Supco                        Q108

Napco                        NS247

Johnstone                  L37-544



HS24A341 SPST Heat Sequencer, 1 Timing, 1 Switches (1 element or 3KW - 5KW)

Diversitech               DGS101

Gemline                   GS101

Goodman                B1290906

Industry No.             60000A0M

Klixon                       60000AO64

Klixon                       60000AOM

Klixon                       60000AOMA012

Lennox                    12F20

Lennox                    58C9701

Mars                        33241

Mars                        33841

Robertshaw             611-241

Supco                      Q101

White-Rodgers        24A34-1

York                         525-37322-000

Napco                      NS101

Watsco                    TDR10

Global                      24CZ-1

Global                      24ZC1

Zettler                        ZC24A34-1

Zettler                        ZC24A341-1

Interstate Electric       IES24A34-1

A1 Components          TDR10

Therm-O-Disc             12S20



Carrier                        40CF680020

Carrier                       1056789

Diversitech                 DGS102

Gemline                     GS102

Klixon                         5117222

Klixon                          60000AOME17

Klixon                          6000A0NI-97

Klixon                          A012

Mars                           33222

Mars                           33842

Robertshaw                611-242

Supco                        Q102   

White-Rodgers          24A342 

White-Rodgers           F77-5410

York                             525-37322-000

Napco                          NS102

Watsco                       TDR15

Global                         24ZC-2

Zettler                         ZC24A34-2

Interstate Electric        IES24A34-2

A1 Components         TDR15

Therm-O-Disc             12S20


HS24A343 DPST Heat Sequencer, 1 Timing, 2 Switches (2 elements or 10KW)

Carrier                         1056789

Carrier                         HN67QC005

Carrier                         HQ1056789

Diversitech                  DGS103

Gemline                      GS103

Goodman                 1256504

Goodman                 BT1256504

Heil Quaker               1056789

Heil Quaker               HQ1056789

ICP                            1056789

ICP                            HN67QC005

ICP                            HQ1056789

Janitrol                      1256504

Janitrol                      BT1256504



HS24A344 DPST Heat Sequencer, 1 Timing, 2 Switches (2 elements or 10KW)


Carrier                     HN67QC006 

Diversitech               DGS104

Gemline                   GS104

Goodman               BT1256504

Supco                     Q103     

ICP                          HN67QC006  

Klixon                       60000EO49

Mars                        33245

Mars                        33845

Supco                     Q104

White-Rodgers       24A34-4 

White-Rodgers        F77-5412

York                         525-37325-000

Napco                     NS104

Watsco                   TDR25

Global                     24ZC-4

Zettler                     ZC24A34-4

Interstate Electric    IES24A34-4

A1 Components    TDR25

Therm-O-Disc        12S22





HS24A345 Packard   DPST-SPST Heat Sequencer, 2 Timings, 3 Switches (3 elements or 15KW)

Nordyne                     621678R

Nordyne                     01-0842 

Coleman                     S1-02435341000

Coleman                     024-35341-000

Coleman                     3400-357 

Coleman                     3400-3571    

Coleman                     3115-357 

Coleman                     3115-3571 

Coleman                     3115-3571R

Nordyne                     01-0842 

Nordyne                     621678

Goodman                   B1256553

Goodman                   B12565-53 

Johnstone                   L41-691 

Honeywell                  R24CB4007 

Johnstone                   L39-278

White-Rodgers           24A34-5 , F77-5413

Global                         24ZC-5

Mars                           33232 & 33832

Klixon                         51172-32

Diversitech                 DGS105

Gemline                     GS105;

Interstate Electric      IES24A34-5 

Napco                         NS105

Supco                        Q105 

Watsco                       TDR30

Zettler                         ZC24A34-5



HS24A346 Packard 2 DPST Heat Sequencer, 2 Timings, 4 Switches (4 elements or 20KW)

Coleman                     3120-3571

Coleman                     3400-3581

Coleman                     3120-3381

Coleman                     3120A357

Coleman                    3120A3571

Coleman                    3120-3391

Carrier                        HN67QC008

Carrier                        P284-1313

Coleman                     3120A357 

Diversitech                  DGS106

Gemline                      GS106

Carrier                        HN67QG005

ICP                              P284-1313 

Klixon                          5117233

Mars                            33233

Mars                            33833 

Supco                         Q106

White-Rodgers          24A346

White-Rodgers            F77-5414

Napco                         NS106

Global                         24ZC-6

Zettler                         ZC24Z34-6 

Zettler                         ZC24Z34-6 

Interstate Electric        IES24A34-6

Therm-O-Disc            15S22

Nordyne                     01-0843

Nordyne                     621679R

Goodman                    B12565554

Goodman                    B125655-54

Honeywell                  R24DB4005

Honeywell                   R24CB4005

Johnstone                   L39-279

White-Rodgers           24A34-6

White-Rodgers           F77-5414

Nordyne                           621679R



HS24A3414 Packard 2DPDT-SPST Heat Sequencer, 4 Timings, 5 Switches (5 elements or 25KW - 30KW)

Diversitech                 DGS107

Gemline                   GS107

Klixon                        511721315

Mars                         33848

Robertshaw              611-007

Supco                       Q107

White-Rodgers        24A34-14

York                         525-37328-000

Honeywell               R8330D1039

Napco                      NS107

Zettler                      ZC24A34-14

Therm-O-Disc         15S241

Klixon                       60000EOM51172

Klixon                       E017

Klixon                       EO17

Mars                        33244

Mars                        33844

Supco                     Q103

White-Rodgers       24A34-3

White-Rodgers         F77-5411

Napco                      NS103

Watsco                    TDR20

Global                      24ZC-3

Zettler                      ZC24A34-3

Interstate Electric     IES24A34-3

A1 Components      TDR20

Therm-O-Disc          12S22

Rheem-Ruud          42-21279-06