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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22541
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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I have a Coleman Evcon DGAT056BDE in the mobile home I purchased

Customer Question

I have a Coleman Evcon DGAT056BDE in the mobile home I purchased 2 years ago and use as a cabin. We generally use a wood stove to heat it but the furnace is used to get it warmed up when we get there. The last 2 times we were at the cabin the blower fan has come on at random intervals with the thermostat being turned off - no burner on. It might stay off for several hours then turns itself on and runs for 10-20 minutes and will repeat this. I figure it might be one of the relays on the board shorting but the schematic on the furnace doesn't even show the relays so I don't know what is controlling them and what the electrical path is. I assume that once the relay is turned on, the path would take it through some limit switches that would normally be open and keep the fan from running but maybe not?? If you know where I could get a schematic that would be great - or any other ideas?
Submitted: 6 years ago.
Category: HVAC
Expert:  BillyHvac replied 6 years ago.


Does this happen when hot out?



Customer: replied 6 years ago.
Not really - last 2 times there it was probably in the 60's
Expert:  BillyHvac replied 6 years ago. ac on the unit?



Customer: replied 6 years ago.
Expert:  BillyHvac replied 6 years ago.


Thank you.


In that case the only thing that can bring on the blower is part 7975-3281 blower switch.


It is apparently weak and making nuisance contact. It is 120 degree f switch with a 20 degreef differential. This switch is bad/weak.



Customer: replied 6 years ago.
Parts list I reference does not indicate it being used on model BDE? Also cannot find any reference to it on the schematic on the furnace - picture attached. Any idea where it is?
Expert:  BillyHvac replied 6 years ago.
just a moment and I wll verify
Expert:  BillyHvac replied 6 years ago.


You are correct...same scenario but is logic board. 7990-320p


see here -



Customer: replied 6 years ago.
Yup that is what I was looking at too ... so are you saying that the control board is bad?
Expert:  BillyHvac replied 6 years ago.

Sorry, lost connection.


That is correct. The blower function on te circuit board is defective but it requires replacement of the whole board.



Customer: replied 6 years ago.
Any way to get schematic that shows electric path - don't want to replace whole board for a $10 relay. I pretty much knew it was probably the relay but without the detailed schematic that shows what controls it there was not much I could do to test it - that is why I thought I would try here - had good luck with Justanswer when I had a problem with my car. Guess I will keep checking around.
Expert:  BillyHvac replied 6 years ago.

I will look for the schematic....but it is going to be of little help. Without cooling there is only one contact point to trun blower on....not the usual 2 or 3.


So if the blower is coming on it means that one contact point is closing. It cannot be blamed on anything else. I will look for the schematic for you.



Customer: replied 6 years ago.
I guess I felt that if I knew which relay it was and what controled it I could at least use a voltmeter to determine if it was being tripped when it shouldn't be due to a bad control signal or if the relay was tripping / shorting internally. Most of the schematics I have found for the Coleman furnaces show the relay in the circuit and what controls it but mine does not have this. I am assuming that the furnace uses 24v for the control signal ... if so I could check the relay for the presence or lack of this signal when the blower is running on it own and if there is no 24v present I would know that the problem is within the realy.
Expert:  BillyHvac replied 6 years ago.

That is the issue with schematics involving circuit boards. The blower operation is all done internally on the board. With ac there is an external signal. But no ac = all blower activity is controlled via a relay and timer on board....and circuit board diagrams are not present on schematics because they are not field serviceable.


I have checked for the DGAT schematic and have found it is not well supported with online documentation. The furnace is a builders grade that hits a affordable price point without too many features or options.


I apologize but I will not be able to supply a schematic....and even if I could it will not show circuit board detail.


I wish you luck!



Customer: replied 6 years ago.
I don't think this was much of an answer. Plan to request a refund. The same place that I referenced regarding the lack of a fan switch on the model BDE said it was probably a bad relay on the control board on their free forum - I was hoping for a schematic or information how to test it not just "replace the control board".
Expert:  BillyHvac replied 6 years ago.


That is what is terrific on this site. If a contractor came to your home and said the exact same thing, you cannot say "I dont think that is much of an answer" and not pay the bill.


The end result is the same no matter how it is addressed - The control needs to be replaced. Whether free forum or contractor or paid answer site - the answer is correct and does not change result.


I really dont know what could have been satisfactory...The relay on the circuit board is not even on schematics as the circuit board is shown as a component and not broken down in drawings. Plus you cannot repair just the relay on the board.


I thank you for your time and will opt out...and I wish you luck on replacing the circuit board.

Customer: replied 6 years ago.
The mobilehomerepair site that both of us referenced will repair boards for $50 + parts and they specifically talk about relays - my goal was to be able to test it and replace it myself.

I do thank you for trying to help me.
Expert:  BillyHvac replied 6 years ago.



The expert has opted out and no longer posting responses to this thread.

The question has been opened for other experts to evaluate.


Comments - Answer provided, customer not satisfied.