Coleman Model 7706-656 Fan Switch Problem

[bmwmick]

I have a Coleman Model 7706-656 Furnace with A/C in my modular home. The fan switch quit working and I replaced it with a new fan switch (S1-7975--3281) which is the crossover number for the original part. Now, my blower motor starts and stops repeatedly when heat is called for, the burner stays lit. I believe they gave me the wrong switch or this switch is defective. This replacement is rated 110-20F. Would the 8866-3281 Fan Switch rated for F130-35F work better in this application?
Thanks,
Mick
Santa Paula, ca.

[Robert]

Hi Mick,

Need to stay with the designated fan switch for your furnace. If you believe it is wrong one or defective, take or send it back.


What is the p/n on the switch ? That will let you know if it is the correct one or not.



Thanks,
Robert

[bmwmick]

Thanks Robert,
As stated above it's a S1-7975--3281 switch. Rated at 110-20F. I don't have the original switch as this was supposedly a direct replacement at a local HVAC company in town. Do you know where I could find the original parts catalog for this furnace?

Mick

[Robert]

Hi Mick,

You can order a parts and wiring diagram here from us :

http://www.hvacmanuals.com/


I just looked your furnace up and the 7975-3281 is the correct replacement.


Will need to test heating circuit with a volt meter to find where the interruption is at.



Thanks,
Robert

[bmwmick]

Hi Mick,

You can order a parts and wiring diagram here from us :

http://www.hvacmanuals.com/


I just looked your furnace up and the 7975-3281 is the correct replacement.


Will need to test heating circuit with a volt meter to find where the interruption is at.



Thanks,
Robert

Thanks Robert,
I've done that already. The fan switch shows line voltage (115VAC) when the blower stops. The burner is still lit and remains lit until the room temp finally comes up to the setpoint.
I looked at your manuals and could not find my model. I have the wiring diagram on the
electrical box cover.

Mick

[Robert]

Hi Mick, you can call Mark toll free Tuesday and he can print off a parts list for you I'm sure if it is not listed in the link. He is still adding to it.


Did the switch have 115vac at both terminals to ground when the blower stopped ?


Thanks,
Robert

[bmwmick]

Hi Mick, you can call Mark toll free Tuesday and he can print off a parts list for you I'm sure if it is not listed in the link. He is still adding to it.


Did the switch have 115vac at both terminals to ground when the blower stopped ?

Thanks,
Robert

No, Only the Black wire had 115VAC the other one is Orange and it was 0VAC to ground.

The furnace was working perfectly until the fan switch died. Nice large blue flame at the
burner.

Mick

[Robert]

Hi Mick,

Did the furnace feel overly hot at the time the blower quit ?

Were you getting a normal amount of airflow from all the registers with normal feel of heat at the time ?


What are the limit temps on your limit switches ?


Thanks,
Robert

[bmwmick]

Hi Mick,

Did the furnace feel overly hot at the time the blower quit ?

Were you getting a normal amount of airflow from all the registers with normal feel of heat at the time ?

What are the limit temps on your limit switches ?


Thanks,
Robert

Robert,
Yes it was hot once when the original fan switch died. The overtemp limit tripped
but it has a manual reset and it reset first try.

Normal airflow up to the failure of the fan switch. Now I get the cycling.

I have no idea what the limit temps are. The Fan/limit switch is rated at 110-20F as stated
above. Is there another limit switch somewhere?

Thanks,
Mick

[Robert]

Hi Mick,

There is a lower limit at bottom of control box below the fan switch.

These type problems can be hard to find, especially from here. may be time to get an hvac tech out to troubleshoot it and diagnose the problem.


Would need to test all components with volt meter while at same time testing temps to see what was opening and if it was supposed to.


Thanks,
Robert

[bmwmick]

Hi Mick,

There is a lower limit at bottom of control box below the fan switch.

These type problems can be hard to find, especially from here. may be time to get an hvac tech out to troubleshoot it and diagnose the problem.


Would need to test all components with volt meter while at same time testing temps to see what was opening and if it was supposed to.


Thanks,
Robert

Yes, The lower limit is at the bottom of the electrical box and it never opens. The only
switch that opens is the fan switch. I just did some more testing and turned the thermostat up
to call for heat and let the furnace heat up for about 20 seconds longer than it does when
it's cycling and the fan stayed on till the set point was reached with no cycling. I'm pretty
convinced that the fan switch is defective and it's closing before it should, never letting
the airbox warm enough.
Thanks,
Mick

[Robert]

Hi Mick,

You have to test temps in order to know what the fan switch is or is not doing.

There are several variables as to what can make a fan switch trip.



Thanks,
Robert

[bmwmick]

Hi Mick,

You have to test temps in order to know what the fan switch is or is not doing.

There are several variables as to what can make a fan switch trip.

Thanks,
Robert

Hmmmmm,
This one only reacts to air temp.
I took the replacement switch back today and installed another of the same P/N.
Blower motor comes on and stays on. Fixed.
Thanks for your time.

Mick

[Robert]

You're very welcome, happy to help.


Thanks,
Robert