Blower problem

Questions about repairs and parts for Nordyne furnaces, air conditioners and heat pumps for manufactured homes including Intertherm, Mac and Miller brands. Click here for Nordyne parts.

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grodzewicz

I have a 1990 mobile home with a coleman 7900 series furnace that was upgraded to central air with nordyne AA* evporator coils and a model 901649 Heating/Cooling Blower. As of yesterday the blower will not start. I got it to start for a few minutes at a time while i was fliping back and forth between heat and cool and trying to adjust the homes thermostat but it only circulated the air the air it was moving was not cooled and the central air unit outside didn't start. When I turn it to heat and raise the thermostat to a temperature above the current temperature the burner starts and runs but again no blower. Also turning the fan switch from auto to on does nothing. Everything worked fine up until last night. This is a very warm time of year around here during the days any help is greatly appreciated. I am hoping it might be something simple like the blower relay but I do not know how to test this. I have a digital multimeter and am very familiar with 12vdc neg ground systems but know nothing when it comes to alternating current or HVAC systems
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Robert
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Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Hi,

How many wires connect at t-stat ? If it is two, place t-stat to HEAT and two switches at furnace control box to COOL and AUTO.

Set t-stat temp lever at 65* for testing operation.


When in above modes, is it JUST the blower inside not working or is it the blower AND outside condenser unit also not working.

Your post was not clear on this.


Will post more when you reply back. Will be later this evening, but I will post more tonight.


Thanks,
Robert
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?
grodzewicz

Hi sorry about that it is both the blower inside and the unit outside that are not working. The furnace model number is 7956b396 I forgot that on the last post too. I found the thread in the coleman section that was very similar to my problem. I also only have two wires from the thermostat. I have tested the voltage on the 15va transformer in the electrical box on the furnace 121 and 28. I jumpered the fan switch in that box also and the inside blower works non stop nomatter the position of any switches except the main power switch. Thanks fo r the help and the speedy reply.
grodzewicz

I just pulled the panel on the condenser outside and found the transformer and tried to test only to find that the outside unit is getting no power. There is a fuse box on the back of the home with two bus fuses in it one of these is blown there is 240vac going into the fuse box I verified this with the multi meter as it is after 10PM here I have no way of getting a new fuse tonight to see if the condenser comes on and cools the air when the fan switch is jumpered. Any other Ideas of things that I need to check are greatly appreciated.
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Robert
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Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Hi,

Remove the jumper and tell me what is and is not working. You've said blower motor doesn't work and also that it runs non-stop.


Put everything back at normal positions with no jumpers and t-stat set to HEAT/65* and furnace set to COOL and AUTO.


What does or does not work ?

You need to locate reason for fuse blowing.


The blower relay controls the blower motor, but has no bearing on condenser unit outside.


This could be a low voltage and line voltage problem and may need the experience of a Tech to sort out.

Trace 240V wires from breaker to outside wall disconnect.


With condenser and blower not working, could be a problem with t-stat reversing relay in furnace control box.


You would have to be able to read the wiring diagram and trace both low and line voltage circuits from beginning to end to find the problem(s).


Check for loose wiring connections at ALL connections.

May just be the blown fuse and whatever caused it. That, depending on wiring could have took out that leg and thus rendered all non-working.

Those are not overcurrent fuses, so usually just blow when loose fitting, old or shorted.



Thanks,
Robert
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?
grodzewicz

Replaced the fuses in the outside box and now all is working fine checked wire from back of fuse box outside until it goes up into the belly every thing looks perfect no breaks in the insulation no kinks. The wire coming out of the box is run in steel flex conduit no sharp bends or kinks/dents etc. The fuses in the box did look quite old though, the only way I knew what to replace them with was the stamped number on the endpiece. the labels were weathered beyond legibility. There are no other signs of why the fuse went bad except maybe age like robert said was possible. Thank you for all the help.
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Robert
Moderator
Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Hi,

You're very welcome, glad it is running again.


Take care and best wishes,
Robert
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?
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