mobilehomerepair.com

Hi im new to this site but i own an older mobile home and am making improvements to it.
I have a coleman presidential II 7670-856 that runs off gas. The furnace has been running fine but its coming up on winter and i decided to clean the furnace out because the wrong filter was used and it had never been done before. I pulled the blower out and cleaned out a lot of dust and dirt with brushes and compressed air. put it back together the same way But now when the furnace runs it runs longer. It doesn't seem to blow hot air like it used to it now blows just warm.

Oh an BTW I have a digital thermostat that has been working since installed over a year ago. So this morning while reading the news and drinking coffee i made a time line of my heater may be of some help to you.

9:18 am furnace kicks on, exchaqnger heat's.
9:19 am Blower kicks on.
9:20 am Exchanger turns off, Blower still running.
9:22 am Exchanger turns on again. Blower still running.
9:24 am Exchanger turns off, Blower still running
9:26 am Exchanger turns on. Blower still running.
9:27 am Exchanger turns off, Blower still running
9:30 am Exchanger turns on, Blower still running.
9:31 am Exchanger turns off, Blower still running.
9:34 am Exchanger turns on, Blower still running.
9:35 am Exchanger turns off, Blower still running.
9:38 am Exchanger turns on, Blower still running.
9:39 am Exchanger turns off, Blower still running.
9:42 am Exchanger turns on, Blower still running.
9:43 am Exchanger turns off, Blower still running.
9:46 am Exchanger turns on, Blower still running.
9:47 am Exchanger turns off, Blower still running.
9:50 am Exchanger turns on, Blower still running.
9:51 am Exchanger turns off, Blower still running.
9:54 am Exchanger turns on, Blower still running.
9:55 am Exchanger turns off, Blower still running.
9:58 am Exchanger turns on, Blower still running.
9:59 am Exchanger turns off, Blower still running.
10:02 am Exchanger turns on, Blower still running.
10:04 am Exchanger turns off, Bower still running.
10:06 am Exchanger turns on, Blower still running.
10:07 am Exchanger turns off, Bower still running.
10:11 am Exchanger turns on, Bower still running.
10:12 am Exchanger turns off, Bower still running.
10:14 am Exchanger turns on, Bower still running.
10:14 am Exchanger turns off, Bower still running.
10:26 am Blower motor shuts down.

Would need to test at gas valve to see if it was getting a call for heat each time the burner kicked on and off.


Blower will keep running with burner kicking on and off so quickly.


Thanks,
Robert

ok i have a multi meter it should be 24 correct?

Yes, 24vac at gas valve continuous from call for heat at t-stat until t-stat is satisfied.


So see if it is there at start and then does it come and go with each on/off sequence ?



Thanks,
Robert

Ok i got my multi meter out and put ground on bare metal and red on both white and black wires on valve and its not reading anything on my multimeter move up to the fan switch and lower limit and its reading 159 noting on 2 gas valve wires when exchanger fires up both sides of switch read 159 still nothing at valve wires

I wanted to correct myself i had a short in my meter. I got another meter and im getting 34v when the exchanger is on then when it clicks it looses voltage and shuts off.

When the room temp drops below the setting of temp at t-stat, then you should get a call for heat at gas valve and it should remain until the t-stat is satisfied and room temp desired is met.


Cutting on and off could be a short, loose wire, bad t-stat,etc....


Also, 34vac is too high voltage, should not be above 28vac. May want to check your transformer load voltage and also be sure your meter is accurate.



Thanks,
Robert

So i did like you said and checked the load voltage. Red and blue wire and its still reading 38 volts. Does this mean this is bad? Could something have happened when i turned the power to it off. And i double checked all connections

What is the line side voltage ? Yes, 38vac is too high. Does the low voltage come and go with the on and off sequences.


Thanks,
Robert

yeah i hear a click and the signal to the valve goes to 0 the click is coming from lower limit switch.

Unless furnace is overly HOT, limit switch should not be opening. Jumper the limit if furnace is not overly HOT and see if cycle runs normal.


Thanks,
Robert

well i jumpered it like you said and the exchanger heated up fan kicked on and i heard that limit switch click but with the jumper wire in there it ran like it did before i cleaned the blower out.

I replaced the lower limit switch with the same one new and still doing the same thing. Also the t stat dosent stop the call for heat unitl the right temp is reached. I turned the furnace on and used my temp gun and the air coming out of the vent reached a temp of about 104. then the exchanger shuts off. it seems when the temp coming out of the vent reaches 88deg the exchanger will heat till the air coming out of the vent reacheas about 104deg and repeats.

At this point without me being there, all I can say is this. Look at wiring diagram and trace the heating circuit and write down each component in order they energize.


Then when it shuts off, be prepared to quickly test each one until you locate where the voltage was interrupted at.

Then try and determine why it is opening and shutting down the cycle.

Look for cool air getting to limits, opening in duct work, etc... . Have to determine what first, then is it faulty or doing the job it was designed for.


Also, inspect the burner orifice for a spider/web, this may be causing it to do this as it is not getting hot enough since the added airflow from blower being cleaned.



Thanks,
Robert