Coleman Evcon exhaust motor runs, but furnace won't ignite

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Coleman Evcon exhaust motor runs, but furnace won't ignite

Postby garlinto » Tue Nov 06, 2007 9:45 pm

I have a Coleman Evcon #DGAT095ADA (SN#931067587). When the t-stat calls for heat, the exhaust fan comes on, but nothing else happens. It will run this way for hours. I have to either turn down the t-stat or manually shutoff the furnace.

I do have a multimeter and know how to use it, but don't really know where to start troubleshooting the problem. Any input you may have will be very helpful!
garlinto
 

RE: Coleman Evcon exhaust motor runs, but furnace won't igni

Postby garlinto » Wed Nov 07, 2007 10:15 am

To be more specific:

When the t-stat calls for heat, the exhaust fan comes on for a specified period of time, at the end of which the igniter comes on. Once the igniter reaches full temperature, the gas valve opens and the flame lights. When the heat exchanger reaches a certain temp, the blower turns on and the house gets nice and toasty.

So in my case, I never get past the exhaust fan stage. I know I have sufficient propane at the gas valve, but I am not wure what else to check.
garlinto
 

RE: Coleman Evcon exhaust motor runs, but furnace won't igni

Postby Robert » Sat Nov 10, 2007 9:31 am

http://www.mobilehomerepair.com/media/i ... 4-0041.jpg


On call for heat and booster motor starts running, wait a few seconds and test across TH and GND for 24-28VAC.


IF you never get that reading, then test at motor connector to see if it is getting 120VAC.


IF motor is receiving 120vac and running steady, but you never get 24-28vac at TH to GND, then the booster motor and/or cent. switch are most likely bad.


Let me know what you read.



Thanks,
Robert
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RE: Coleman Evcon exhaust motor runs, but furnace won't igni

Postby garlinto » Sat Nov 10, 2007 4:04 pm

Thanks!

Actually, I had already tested that, but was unsure of my results.

The transformer, on the load side, has a red wire on one end and yellow wires on the other. When I go from TH to GROUND with the motor running, I don't get anything, only like 325 mV. But if I go from TH to one of the yellow wires on the transformer (not the sole red one at any rate), I get 24V.

So I'm not sure if that tells you anything. I won't be back home till Monday night, at which point I'll retest the TH to GROUND and perform the other test as well. Thanks for the input!!
garlinto
 

RE: Coleman Evcon exhaust motor runs, but furnace won't igni

Postby Robert » Tue Nov 13, 2007 7:05 am

TH to GND on the module.


Thanks,
Robert
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Re: RE: Coleman Evcon exhaust motor runs, but furnace won't

Postby garlinto » Tue Nov 13, 2007 11:11 am

Robert wrote:TH to GND on the module.


Ok, tested as per your instructions.

Results: When the furnace receives a call for heat, I do not read 24-28V at TH to GND (on module).

The centrifugal switch is the one near the booster motor that is round and says Synchron on the outside right? I disconnected one end of it (not the wire coming from the transformer but the other end) and read a steady couple of millivolts as well as 20ohms across the switch. This reading (ohms) didn't change whether the furnace was on or off.

In addition, the booster motor is indeed receiving 118.5VAC and running smoothly.

Diagnosis?
garlinto
 

RE: Coleman Evcon exhaust motor runs, but furnace won't igni

Postby Robert » Tue Nov 13, 2007 12:26 pm

IF the air pipe is clear and booster motor is running full rpm's, then the centrifugal switch should close sending 24-28vac to TH / GND.


If not, one or both is most likely bad. I'm not there to test myself though. When Booster Motor runs and cent. switch closes, a 24-28vac signal goes to TH / GND.


The cent. switch is inside the motor and cannot be bought seperately.

Booster Motor with Centrifuagl Switch # 7995-3169 @ 4140.27 + $10.00 shipping.


You can see and order it from right side column here through Paypal:

http://www.mobilehomerepair.com/ColemanGas.html



OR, call toll free after 9AM CST to 1-877-263-7860 and charge to Visa or Mastercard.


If you're in Canada, let me know for added info.



Thanks,
Robert
Last edited by Robert on Wed Nov 14, 2007 1:20 am, edited 1 time in total.
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RE: Coleman Evcon exhaust motor runs, but furnace won't igni

Postby garlinto » Tue Nov 13, 2007 12:48 pm

I just found out something else...

I noticed while looking at the schematic on the side of the booster motor that the BLUE wires were the 24V wires that ran to and from the centrifugal switch. So I traced them back to where they go in an effort to troubleshoot the centrifugal switch itself.

I noticed that one wire comes from the 24V limit switch and the other wire goes through a fuse and to another (high?) limit switch on the main blower housing.

So after poking around with my multimeter, I noticed that I had a 24V potential across the lower 24V limit switch, but was not getting the same potential across the centrifugal switch, meaning that the limit switch was not closing. So I decided to turn on the furnace, and then use an alligator clip to bypass the limit switch, and the furnace immediately clicked on and fired as per it's normal ignition cycle.

So, did I truly find a problem or was this just a hack?
garlinto
 

RE: Coleman Evcon exhaust motor runs, but furnace won't igni

Postby Robert » Wed Nov 14, 2007 1:29 am

Yep, thus my statement above that I'm not there to test myself.

I thought we had already established that, but after looking back I see we had not. My apoligies there.

So cent. switch was closing, but the 24vac signal wasn't getting there.


Now, be sure that the limit is just weak and faulty or is it open for a reason.


Since furnace never fired, probably just weak.




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Robert
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