Greetings,

I have an old electric furnace located in my attic. I cannot determine the mfg/model, but estimate the unit to be ~20+ years old. We have owned the house for 2 1/2 years and have had heater problems each season. In the last two years we have replaced burned out heating elements and the heating sequencers. This year we called a service company and they diagnosed a burnt out element and a bad sequencer. The element was replaced, but I decided to do my own diagnostics on the sequencer before paying (again) for another one. I'm not an HVAC guy but very handy with a voltage meter and home improvement/repairs. Here's what I've found and it doesn't seem correct to me. Can someone provide an opinion on the findings.

Electric furnace info:
Location - Attic
Mfg / model - Unknown
Age - Estimated 20 - 25+ years
Heating type - Electric
Heating element wattage - 5Kw
Number of elements - 3
Sequencer - "Quad"
Number of sequencers - 1

Sequencer diagnostics and wiring info:
Sequencer - two 2-stack units mounted on a base plate. On the base plate is this information:
15SH22 309576
H1-110 C1-110

Sequencer #1 information (from top of sequencer):
T-O-D
12SH22 H24v
308771 A0546

Sequencer #2 information (from top of sequencer):
T-O-D
12SH22 H24v
308734 A0548

Sequencer 1 = M1 & M2, M3 & M4, 24V + / -
Sequencer 2 = M5 & M6, M7 & M8, 24V + / - (the 24v terminals are jumped across pos -> pos, negative -> negative between sequencers)


Diagnostics results with the unit cycling on / off:
With the unit powered off (not calling for heat) M1 / M2 and M3 / M4 carry 240v. When the unit powers on these go to 0v and do not carry voltage until the unit cycles off again.
With the unit powered on (calling for heat) M5 / M6 carry 0v and ~90s later carry 240v. M7 / M8 carry 120v then go to 0v ~90s later, then a little longer go back to 120v.

Question: Is it normal to have sequencers "normally closed" as with M1 / M2 & M3 / M4? Also, is it normal to have a mix of 240v & 120v running across a sequencer stack?


Here's the wiring. The colors are as best as I can determine. Most wires are faded and hard to distinguish the original color:
Note: High temp thermos & heating elements are designated 1 - 3 for information only. I'm presuming they are wired correctly.

There are two (double) breakers at the unit. Breaker 1 = 40amp, breaker 2 = 30amp.
Breaker 1 - Hot (black) -> M1
Breaker 1 - Hot (black) -> M5
Breaker 1 - Hot (black) -> Wiring harness
Breaker 1 - Common (white) -> Wiring harness
Breaker 1 - Common (orange) -> High temp thermo #1
Breaker 1 - Common (orange) -> High temp thermo #2

Breaker 2 - Hot (black) -> M7
Breaker 2 - Common (orange) -> High temp thermo #3

M2 -> (purple) Heating element #1
M3 -> (blue, maybe violet) Wiring harness
M4 -> (brown, maybe violet) Wiring harness
M6 -> (purple) Heating element #2
M8 -> (purple) Heating element #3

High temp thermo #1 -> (red) Heating element #1
High temp thermo #2 -> (red) Heating element #2
High temp thermo #3 -> (red) Wiring Harness

Sequencer 1 - (yellow) 24v+ -> Wiring harness (to fan/thermostat relay box)
Sequencer 2 - (violet, maybe gray) 24v+ -> Wiring harness (to fan/thermostat relay box)
Sequencer 1 - (purple) 24v- -> Wiring harness (to fan/thermostat relay box)
Sequencer 2 - (purple) 24v- -> Pigtail from 24v-

Question: Is it possible that the 24v wires are simply reversed, in turn causing the normally closed condition on sequencer #1?

Thanks in advance for any comments and feedback.

Sincerely,
Greg Dotts

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