Coleman 7956-856

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Coleman 7956-856

Postby Bealed » Sun Jan 10, 2010 1:19 pm

Hi all, Found this forum a few days ago (when it got REALLY cold of course) but I can't quite find an answer to my heat problems. I hope you don't mind me getting straight to the point.... its is VERY COLD right now.

I have a Coleman 7956-856 central heat and a/c (at least a 1985 model- so it doesn't have the self diagnostics). Until last year, even with very low temperatures outside, it gave out some wicked heat. It would actually run you out of the house :). Last year I noticed that it wasn't quite as much heat. This year, it really matters because of the recent arctic blast (sustained lows of 15-20 degrees when it is normally around mid 30's) and I have had to get a few electric space heaters, which I DO NOT like at all (going to be a huge power bill this month).

The air flow is fine- blower still performing well and I cleaned the A-coil back in the summer. Pilot and burner seem to be working well. There is just not enough heat coming through.

Two months ago, in an effort to increase efficiency and heating,I removed the burner/pilot assembly (thermocoupler?) and vacuumed out a good amount of material (soot, rust?) from the heat exchanger. That did not solve the problem - still very little heat making it through the vents even though the burner seems to be working well.

Today I noticed that the chute (exhaust vent?) that runs up beside the blower to the chimney/flue is not hot at all. It should be hotter than a firecracker, right? And the heat exchanger doesn't feel as warm as I think it should be. I also noticed that the manual reset button may not be functional (does not seem to move when pressed).

Any ideas on further troubleshooting?

Thanks,
Bill
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Re: Coleman 7956-856

Postby Robert » Mon Jan 18, 2010 10:42 pm

Hi Bill,

Place a thermometer in the louvered front door return air panel.

Then do same at nearest floor register.

Give me the readings.




Thanks,
Robert
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Re: Coleman 7956-856

Postby Bealed » Tue Jan 19, 2010 1:26 am

Robert,
It has warmed up considerably here now. mid 30's instead of teens. But turning the thermostat up to about 75 at the thermostat...
68 degrees at the return air panel
(by "floor register" I assume that means vent)... 70.1 degrees at the nearest register

Thanks!
Bill
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Re: Coleman 7956-856

Postby Robert » Tue Jan 19, 2010 2:03 am

Hi Bill,

Not good at all. You should get between 40 and 70 degrees higher temp at nearest vent than the return air temp if furnace is working properly.

At those temps, you are only getting slightly over 2 degrees of added heat.


Inspect the burner orifice behind the gas valve for clogs (spider-web-eggs), inspect burner to ensure it is clear throughout, test gas pressures (input and manifold),inspect roof-jack/flue for proper operation with no clogs or separations of pipes.


Thanks,
Robert
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Re: Coleman 7956-856

Postby Bealed » Wed Jan 20, 2010 10:32 am

Thanks Robert,
I am 90% sure the flue is intact. It is only about three feet straight up through the roof and I can see it clearly and it is still wrapped. I will inspect the roof jack, but I don't have pressure testing equipment. Looks like I'd better call in an HVAC friend.

Thanks for the advice.

Bill
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Re: Coleman 7956-856

Postby Robert » Wed Jan 20, 2010 12:30 pm

Hi Bill,

You're very welcome, happy to help.



Take care and best wishes,
Robert
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Re: Coleman 7956-856

Postby Bealed » Tue Jan 26, 2010 5:42 pm

Robert,
I wanted to give you an update. Your suggestions helped.

After reading your suggestion, I went back and looked at a few things. The air flow at the registers just wasn't what I thought it should be. Remembering how much I had cleaned out of the heat chamber, I looked at the blower.

I pulled the blower, took it apart and cleaned what I am sure was about 2 lbs of dirt and dust from the blades and housing, blew as much out of the motor as I could then reassembled everything and reinstalled the blower. the heat exchanger looked go- no cracks, or openings that I could detect.

I also pulled the burner, and used canned air to clean soot from the pilot light and burner and used a small wire brush to clean the thermocouple as much as I could. I don't think this unit has ever been cleaned. :oops:

I turned the thermonstat up to about 90 and tested the temperatures with a wireless indoor outdoor thermometer (Pretty handy for that purpose). I now get 72 intake and 85 at the register.

But I don't think it is running as long as it should be. Once the burner lights and warms up, the blower runs for about 2 and a half to 3 minutes, then stops. But, I can hear the burner still going. It warms up for a bout two more minutes, then cycles again. The burner runs the entire time. So it is "keeping up" with the temperature, but not getting ahead of it, so to speak.

I tried adjusting the anticipator on the thermostat, but I can't see that much difference.

Should I replace the thermocouple? Would that help? :?

Thanks,
Bill
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Re: Coleman 7956-856

Postby Robert » Tue Jan 26, 2010 7:46 pm

Hi Bill,

That is still way to low of a supply temp, I would call an hvac tech before going further to see what is needed exactly.


Thanks,
Robert
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Re: Coleman 7956-856

Postby Bealed » Tue Jan 26, 2010 8:02 pm

Ok Thanks!
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Re: Coleman 7956-856

Postby Robert » Tue Jan 26, 2010 11:22 pm

You're very welcome, happy to help.



Take care and best wishes,
Robert
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