Coleman furnace fan comes one even with Thermostat disconnected

[DON]

Does anyone have a repair parts manual or just manual for coleman furnace 4225A?  Having issues and can't pinpoint problem.  May need to see if I can replace some hard to find parts.  Blower motor will come on even with themostat disconnected.  Does not heat when that happens.  Pilot too high?  When motor cycles on too often like this, does something tell the furnace not to heat?  Stymied.  Thanks. 

[strykersd]

I don't have the answer as I'm dealing with similar issues with mine.  Maybe this could help?  http://www.classicwinnebagos.com/forum/index.php?topic=2640.0

[RANGERRICK]

I have some parts books,not sure if i have the book for that model.I also have parts if know what you need.

[DON]

This furnace is work in progress.  The model is 4225A.  I will get back to you if can't find possible needed parts.  Thanks.

[HVACguy]

Ok, I have never had my hands on an RV furnace ( I fly to NM to pick up my first RV  in 12 days and drive it home to TN.
) , but they cant be much different than the many different residential furnaces I have worked on over the years. So going into this blind so to speak. It sounds like one of 2 issues.


1. High limit is tripped/open. When this happens on many residential furnaces i.e. Carrier, the fan will run non stop and furnace will not ignite.
    you may have a manual reset limit, this is normally a small ( nickel or quarter sized device located somewhere on the fire box, and could possibly be one somewhere on blower wheel housing as well. It normally has 2 wires going into it, and a small red button in center. If you see this try pressing button to reset.


If it is a pop disc auto reset, you need to remove the wires from the male spade connectors and check continuity with a meter. you should have signal if it is closed and good, no continuity means it stuck open and will need to be replaced. I would check continuity on a manual reset the same way to make sure its still good.


2. Fan control has failed, this is unlikely as furnace should still fire up, you would just have continuous fan and no timed cycling.


I will say to add confusion, sometimes you have a combination fan/limit control...these usually have 4 wires into them, and a round dial marked with temps on them with a small 0n/off slider on the disc. sometimes these are behind a silver rectangular box/cover mounted on the firebox  most of them are Honeywell products.


Hope this might help!

[DaveVA78Chieftain]

Hmm, this is fun one!
Operation and Service Manual is in the Member area.

Blower motor will come on even with themostat disconnected.

Based on the wiring diagram:
I would say either the relay is stuck closed OR the fan switch is ON (appears to bypass the relay).  The thermostat controls the relay.
The blower should still stop if you depress the manual glow coil button.

[DON]

Thank you for the info.  Always educational. 

[DON]

I just purchased a adjustable thermodisc thermostat that goes to 135 temp.  My heater motor comes on even with thermostat disconnected.  The thermostat on it was rated up to 125.  I guess the heater, because of the pilot light, is getting hot and the motor will kick on.  Is there a thermostat that has a 140 or so rating that might eliminate this problem?  I am concerned with safety, of course.  Do not know too much about these things.  I think the new thermostat is better, but still periodically motor kicks on.  Wish I had a parts manual for coleman 4225A. Do not know what heater was supposed to have, parts wise.  Maybe 125 thermostat was replacement before I purchased motorhome.  Original should have been higher range.  Tried adjusting pilot light.

[DON]

Put new thermostat but range may still not be high enough.  Do not know.  Thanks, Rick. 

[DaveVA78Chieftain]

I take it you did not download the manual because if you had looked at the wiring diagram you would see that:
1) the thermostat and the limit switch are in series so if the thermostat is not installed the limit switch does not get any power.
2) the thermostat controls the coil of the relay that supplies power to the relay.  If the thermostat is not connected then you get no power to the relay coil to energize the relay to supply power to the fan motor.
3) the limit switch is always ON so that power can be applied to the gas valve.  The limit switch ONLY opens up when the unit overheats shutting OFF power to the gas valve. NO gas = NO heat

AS I SAID IN MY ORIGINAL POST
Based on the wiring diagram:
either the relay is stuck closed OR the fan switch is ON (bypass' the relay).  The thermostat controls the relay coil.
This is a very simple circuit design.  NO fancy control boards, basically simple series circuit that controls blower motor ON/OFF signal to blower motor relay coil.

Fan switch is your most likely culprit



The only thing for the 4225A NOT shown in that diagram is the glow coil button used to light the pilot light AND remove power from the thermostat.

Has someone rewired your unit so it is operating improperly thereby unsafely?

Coleman Parts  WIll need to locate a RV dealer who procures parts from NTP Distribution.

[Rickf1985]

Uh-Oh......... Now you got Dave riled up! I have not really been following the whole thread so I had not looked at any diagrams posted but it is a pretty simple setup. As Dave said, you might want to see if it has been modified, either by human or rodent means.

[Oz]

If you are a Member or Life Member, one of the most beneficial resources you have is access to the manuals section.  As Dave said, we have this manual and it includes adjustments, service, and troubleshooting. 


Always check to see what we have here for you first, it may save you a lot of time and frustration and will at least give you the basics to start from.

[DON]

Found info in manual section.  Replaced thermodisk.  Fan still comes on with thermostat off.  Turned off fan switch during day.  I put screen on exhaust because of wasp hives when checked out originally.  Has soot around exhaust next morning.  Thought maybe restriction because of screen.  Took screen off.  No soot.  Not sure if that was problem.  Seems to be okay now.  I guess just old technology.  Warming up now.  May not need heater until winter again.  Thanks for the info.