Coleman DGAA090BDTA question

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Coleman DGAA090BDTA question

Postby pigaman » Mon Jul 09, 2007 6:03 am

Hello All
I have a Coleman DGAA090BDTA model AC/Furnace combo. The unit is about 4 years old. I recently returned home after a power interruption of some sort and turned on the A/C. The compressor came on normally and then the blower, but I noticed that there was warm air coming out of the vents. When I checked the furnace, I found that the gas burner was on. There are no error codes. The unit works fine in the heat mode, and I swapped out the thermostat. I suspect that the power event may have damaged the control board. Any help would be appreciated. Thanks
pigaman
 

RE: Coleman DGAA090BDTA question

Postby Mark » Mon Jul 09, 2007 12:03 pm

Hopefully Robert or Hvac1000 can help you with the troubleshooting. But I do know that the board for your furnace is 7990-320P. It can be seen and ordered from this page: http://www.mobilehomerepair.com/ColemanGas.html. When you get to the page, hit 'Control F' and search the page for the part number.

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RE: Coleman DGAA090BDTA question

Postby pigaman » Mon Jul 09, 2007 1:20 pm

Thanks Mark for the reply. I had already located the control board on your site, but thought I might get another opinion. I did find another post which had the opposite problem from mine. His A/C was running at the same time as the burner when in heat mode which was caused by a damaged control board. Thanks again.
pigaman
 

RE: Coleman DGAA090BDTA question

Postby hvac1000 » Mon Jul 09, 2007 11:29 pm

((The unit works fine in the heat mode, and I swapped out the thermostat. ))

So you already changed out the thermostat and the furnace is still running in the A/C mode that solved one possible problem.

Disconnect the W wire in the furnace area and that will eliminate not only the thermostat but also any wiring problem from the thermostat to the furnace.

If after doing this the furnace still runs at the same time as the A/C unit I would then replace the circuit board.

I would also look into a power surge and quality protection device.
Circuit boards, TV sets, and anything electronic is a prime candidate for dirty power or power surges. These devices will protect the very expensive parts inside your appliances.
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RE: Coleman DGAA090BDTA question

Postby pigaman » Thu Jul 12, 2007 7:20 pm

Hello HIVAC
I received the replacement control board today. After installation, I am still having the same problem. I mi-spoke when I said that the heat mode was working OK. I doesn't matter if I set the t-stat for heat or cool, both the A/C and the burner run at the same time. The blend-air relay is working fine also. I must be missing something some where. Any ideas? Thanks again for your help.
pigaman
 

RE: Coleman DGAA090BDTA question

Postby hvac1000 » Thu Jul 12, 2007 9:05 pm

From my pther post.

((Disconnect the W wire in the furnace area and that will eliminate not only the thermostat but also any wiring problem from the thermostat to the furnace. ))

If after doing this the furnace still runs at the same time as the A/C unit I would then replace the circuit board.

Disconnect the wire then try it. Report back.
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RE: Coleman DGAA090BDTA question

Postby pigaman » Fri Jul 13, 2007 3:12 pm

Ok, I disconnected the white wire coming from the t-stat and now the A/C turns on and the burner does not. The A/C will stay on until the temp drops enough to trigger the t-stat off. Am I to assume from this that the problem may be in the cable wiring back to the t-stat and or the t-stat. Again, thanks for the help.
pigaman
 

RE: Coleman DGAA090BDTA question

Postby Robert » Fri Jul 13, 2007 4:34 pm

Hi,

Yes, if disconnecting the W wire at the furnace stopped this from happening, the problem is in the cable between the furnace and t-stat or the t-stat itself.

How many wires are connected at your t-stat ?

If you have a meter to test with, turn power to OFF, place one on on the W disconnected from furnace and other lead on a good ground at furnace.

Have someone turn power back on, do you get a 24vac to 28vac reading ?

IF so, go to t-stat, turn power back OFF, remove cover to reveal wiring and disconnect the W from the t-stat.

Turn power back ON and retest the the W wire to ground at furnace end again, do you still get 24vac to 28vac reading ?


Take care and best wishes,
Robert
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RE: Coleman DGAA090BDTA question

Postby pigaman » Fri Jul 13, 2007 5:10 pm

I have 4 wires at the t-stat. Green(fan), Yellow(coll comp), White(heat control), red(goes to xformer commonfor heat&cool).
No 24 vac from disconnected white wire at furnace to ground. Thanks.
pigaman
 

RE: Coleman DGAA090BDTA question

Postby Robert » Fri Jul 13, 2007 6:36 pm

Turn power OFF, reconnect all disconnected wires to once again get it to come on in both modes, turn power back ON.

Did it still come on in both modes again ?


If so, remove cover at t-stat and place one lead on Red and the other on White. Be very careful to not touch any other terminals at same time.

Do you read 24-28vac or 0vac ?


If it does not happen again, enjoy and if it does happen later, then do this t-stat voltage test.


Thanks,
Robert
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RE: Coleman DGAA090BDTA question

Postby pigaman » Sat Jul 14, 2007 7:59 am

Hi Guys
Ok, I reconnected the white wire in the furnace and turned power back on. It still runs in both modes at once. Here's my t-stat readings.

(Cool Mode) ON
R-W=0v
R-Y=0v
(Cool Mode) OFF
R-W=0v
R-Y=26v

(Heat Mode) ON
R-W=0v
R-Y=0v
(Heat Mode) OFF
R-W=26v
R-Y=0v

Hope this helps. Thanks.
pigaman
 

RE: Coleman DGAA090BDTA question

Postby Robert » Sat Jul 14, 2007 11:25 am

Hi,

I'm not there remember to see what and/or how you are testing or anything.

The results of the tests don't make sense, so lets go another route and try to eliminate this.

Let me explain. You have BOTH modes on at same time. You disconnect White wire at Furnace and the heat stops, reconnect and the heat starts again.

Yet, when you tested the White wire with a good ground, you did NOT get a reading.

By what you stated, the heat was receiving its power from the white wire, yet there was no voltage reading when testing white wire.


Set t-stat to Cool and Auto and 65*.

I assume BOTH Cool and Heat comes on here.


By switching t-stat from COOL to OFF, do BOTH cool and Heat shut offf ?


You must also realize that this may not have anything to do with the power interruption.

It sounds more like two wires becoming bare and touching somewhere in the circuit, most often caused by rubbing against the sharp edge of something or being chewed on my mice.

This will cause a back-feed sometimes also and could explain the non reading when you disconnected the white wire from furnace.


Also, the Red coming from the transformer to the t-stat does NOT
come from the common side of transformer.


Where/what was the White wire connected to at furnace where you disconnected it ?


Thanks,
Robert
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RE: Coleman DGAA090BDTA question

Postby pigaman » Sat Jul 14, 2007 12:22 pm

Hi Robert
I'm not sure why, but I just re-checked the white wire to ground and I do have 25v there when in both cool and heat modes. Maybe I didn't have a good ground when I checked before. You're right, it didn't make sense that the voltage wasn't there if the burner was turning on. I think I will disconnect the cable to the t-stat at both ends and check for shorts wire to wire and to ground. Again, thanks so very much. I realize how hard it is to troubleshoot equiptment without being there.
pigaman
 

RE: Coleman DGAA090BDTA question

Postby Robert » Sat Jul 14, 2007 12:45 pm

Hi,

You're very welcome. When in Cool/Auto mode with Heat on also, when you turn t-stat from Cool to Off, does BOTH modes stop immediately ?

I'm about 99.99% sure your problem is the t-stat or t-stat connections. Be sure the connection are correct and no two are touching.

Turn power to furnace OFF, reconnect all wiring as originally and restore power to see if it still malfunctions.

If so, remove power, disconnect white wire at t-stat and restore power.

Does heat still come on while in Cool mode ?


IF it does, turn power off, remove all wiring from t-stat, set t-stat to COOL and AUTO.

Then set meter to test resistance (ohms) and test across R and W.


Read this and follow carefully to get correct readings and test results.


Thanks,
Robert
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RE: Coleman DGAA090BDTA question

Postby pigaman » Sat Jul 14, 2007 2:11 pm

Hi Robert
First, I checked the cable going to t-stat and cable going to compressor. No shorts to ground or each other. Unit still malfunctions. I disconnected the white wire at the t-stat and unit still malfunctions. Disconnecting the white wire at the furnace mkes it run correctly in cool mode. Disconnected t-stat and took readings.

Cool/auto
ON
R-W=open
R-Y=.8 ohms
OFF
R-W=4.0 ohms
R-Y=open

Heat/auto
ON
R-W=3.0 ohms
R-Y=open
OFF
R-W=open
R-Y=.6 ohms

This seems like what I would expect. Like I said, the wiring all seems to check out ok. I must be missing something somewhere.
pigaman
 

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