Duct Heater is not functioning

HVAC questions and problems within commercial installations.

Duct Heater is not functioning

Postby spartan301 » Mon Dec 12, 2011 11:46 am

Hello,

I have a problem with my commercial duct heater. All the wiring seems to be correct, but for some reason the coils are not heating up.

Now airflow from the main unit is good, the thermostats are set to heat (I have two thermostats, one leading up to the unit, the other leading up to the duct heater for the extra rooms), all power is on.

I replaced the electrical contactor in the duct heater box, and when I have the power on, I can take a rubber hammer or something and gently force the bridge down to make contact. The coils will then heat up, so the coils and the wiring are OK. I think it is a signal problem that is preventing the contactor from transferring power.

I have taken some pictures of the duct heater innards.
In this one, the thermostat wires that don't have their brown covering on the left are the ones which come from the extra thermostat. Then further to the right you can see the other thermostat line, which connects the duct heater to the actual unit. Brand-new contactor also visible. *.us/photo/my-images/507/dsc04386g.jpg/

Here's a picture of the air pressure sensor. When I found it, the wire was on Norm Closed, so I switched it to Norm Open. *.us/photo/my-images/341/dsc04381jl.jpg/

Some more components in the box.
*.us/photo/my-images/542/dsc04383w.jpg/

A wider view. This includes all the stuff from the last two photos.
*.us/photo/my-images/694/dsc04382r.jpg/

Here's a more clear view of the components just under the contactor. That thermostat wire to the right is the one that comes from the unit with the fan. *.us/photo/my-images/829/dsc04385fp.jpg/

Sorry about posting links like this. I need BBC coding to be activated for me, otherwise I cannot embed images. Can any admins help?

Thanks in advance for all your help!
Tom
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- Duct Heater is not functioning

Postby heatseeker » Mon Dec 12, 2011 3:35 pm

sounds like your control voltage for your contactor is being interrupted, probably at the t-stat but possible somewhere else you have to trace it out to find out where-good luck.
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- Duct Heater is not functioning

Postby spartan301 » Mon Dec 12, 2011 4:25 pm

Thanks Heatseeker.

I found out that my thermostat needed new batteries, and the air-pressure switch was wired incorrectly.

Tom
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- Duct Heater is not functioning

Postby heatseeker » Tue Dec 13, 2011 9:58 am

good job you are hired.
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- Duct Heater is not functioning

Postby gibby » Fri Jan 20, 2012 8:59 pm

easy solution to determine the heater problem . forget the stat , jumper across where the stat would connect and now your dealing only with the heater. Check complete control circuit, you may have a manual high limit open but the control circuit is quite simple.
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- Duct Heater is not functioning

Postby heatseeker » Tue Mar 13, 2012 8:28 am

gibby -
> easy solution to determine the heater problem . forget the stat , jumper
> across where the stat would connect and now your dealing only with the
> heater. Check complete control circuit, you may have a manual high limit
> open but the control circuit is quite simple.
Thanks for the useful info.
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- Duct Heater is not functioning

Postby rajendran » Fri Apr 19, 2013 12:59 pm

Duct cleaning will be a good solution for your problem. By cleaning the duct, you can able to make your device to work properly.
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