Coleman 3400A816 heating question.

[wvmedic]

I have a furnace question, Coleman 3400A816.

My furnace seems to have to short of a heating cycles, it will kick on and run for a few minutes the it shuts down then a little while later it goose thru the same process.
So I got to checking the elements and the sequencer.

This unit has three elements, I’m getting 242 vac across the top and bottom but nothing on the middle one after the first few seconds the blower kicks on.

Is this normal?

On the sequencer I’m getting between 16 and 20 vac across the H terminals, 0 on the M terminals when the thermostat calls for heat.

Thanks, Jeff.

[Mark]

What's the anticipator on the thermostat set too?

Mark

[wvmedic]

Mark, it is curently set at 60-f.

Jeff.

[Mark]

Not the temperature setting, the anticipator setting. You might have to take off the cover of the thermostat to read it. It tells you how much of a temperature differential before the furnace shuts off. If its set to low, the furnace will cycle on and off a lot.

Mark

[wvmedic]

Ok, sorry. It is set at .5.

I am going to get a thermometer to put by the thermostat to check its accuracy though.

Thanks Jeff.

[Mark]

I don't have my 3400 manual here at the home office, but I know .5 is too low. Move it up to 1.5 or 2 and see if the furnace runs better.


Mark

[wvmedic]

Ok, thanks I will do that.

How about the middle element only kicking on for just a few seconds after the blower starts then shutting off while the top and bottom elements stay on?

Thanks Jeff.

[Mark]

First test the limit switch. If the limit switch opens during the process, that would explain why its shutting down. If the limit switch is opening, it's either a defective limit switch, or the element is getting too hot and tripping it. Elements are no longer available for your furnace, so to do a repair would take a restring kit sold on this website.

If the limit switch is staying closed, then the issue is probably the sequencer. Sequencer part number for your furnace is 3115-3571. It can be found on this page (along with the restring kit): http://www.mobilehomerepair.com/ColemanElec.html

Mark

[Mark]

Oh, the part number to the limit switch is 3400-3151. Available at the link in the last post.

Mark

[wvmedic]

Mark thanks for your fast replies, how would I test or check the limiter?

Also, my Wife’s cousin is in the HVAC business and replaced the sequencer about two years ago. I don’t think it is the correct one. And this is why I want and need to check things my self. I did work in the business when I was 16 or 17 but just did the plumbing, and making and installing duct work. I learned here how to test the elements and the sequencer. So thank you for this site.

The numbers I found on the sequencer are as follows.

15SH22-------------------------309576
H1-110--------------------------C1-110

Thanks Jeff.

[Mark]

I would have to go into the office and physically look at a heating element to see if those numbers match.

Mark

[wvmedic]

Thats ok Mark, don't do that.

Thanks for your help.

Jeff.

[Robert]

Hi,

The Heat Anticipator actually shuts the furnace off EARLY in order to not overshoot or undershoot the set temp.


It maintains shorter on cycles and shorter off cyles so the home doesn't get too hot when on or too cold when off.


If you have it set at 60*, it cuts off when t-stat surrounding room air is actually around 58*/59*.


Take care and best wishes,
Robert