View Full Version : Question for the pros
06-06-2005, 10:04 PM
I am a commercial/industrial electrician but I have been asked by a national account that I have to check out an RTU for them. According to a local HVAC contractor it is an electrical issue. The only info I have doesn't mean SQUAT to me and I can't get their HVAC guy to call me back. Any help would be greatly appreciated. What he wrote was:
"RTU #2 is in Modd Comm Loss. It is an ETC controller"
Can anyone interpret this for me?
06-06-2005, 10:11 PM
??? Hmmm. Com loss usually is from the controler not sending a signel which I've found is usually due to loss of power to the EMS controler.What powers the Mod? Is it 24 volt,120? Some times it's off the unit other times it's off it's own control box down in the store. Either way unless it's a main breaker I can't see how it would be in your area to check out.
06-06-2005, 10:18 PM
I tend to agree with you, but these folks insist that this is and electrical issue and they want to pay me to drive 60 miles to find out. I just hate to bill them for all that time just to say "too bad, not my problem". Is it possible the EMS controller has a dedicated 110v circuit? Also,what is an "ETC controller"?
06-07-2005, 09:46 AM
I'm not sure what the ETC comtroller is. All the times ive gotten a call for a Mod com loss it's been from the energy managment company stating they cant communicate with the unit.Most of the time though it wasent a problem with the EMS equipment but instead a problem with the unit that caused the fuses to blow.
Most EMS company's do not install thier own equipment. They find a local vendor or have one vendor travel around installing them so each one can be install differently.
Usually there is a control box down in the store that has a dedicated 120 circuit powering it. This control box is for the store's whole HVAC system so the loss of that circuit would make every unit have a com loss and not just one. There is usually a controller for each unit(mounted inside the unit in most cases)that needs 24 volts to operate. In some cases the 24 volts is ran from the control box in the store and in other cases the vendor take 24 volts from the unit it's mounted in. As you can see there isn't much eletrician related problems that could be there.A good technician would be able to determin what the electrical problem was even if he could not repair it and "mod com loss" is way to general of a description.
ETC is short for
Electronic Temp Controller where I come from but I can't figure out where this fits in. Unless they believe the controller (ETC) remote is giving faulty info to the RTU.
That is got to be what they are talking about... On an EMS using a modem communication device to a monitoring center. They can't pick up the ETC or Temp Control reading that senses and controls the RTU #2... Must be a sensor wire broken or short, could be a bad sensor too.
You will find a box in the ceiling just under the RTU where the thermostat wires run out of and into the RTU.
You will find your sensor wiring there and color coded. These wires run from there to the RTU and back to the command box in the back of the store.
Hope you have a wiring diagram.
[Edited by lusker on 06-07-2005 at 11:56 AM]
06-07-2005, 04:32 PM
Thanks guys. The unit was on a Novar System(which I am familiar with) so it was lack of signal from the ETC which prompted the call. The problem was that there wasn't any voltage to the Novar controller b/c the HVAC tech had turned off the power to the unit. This he did b/c the squirrel cage was locked up. I went ahead and replaced the wires the motor had burned up on the xformer and the relay, broke the taps on the motor and left the unit on so they could get a signal from the Novar. I hope I didn't step on anyone's toes by doing that. Thanks again for your input, if I can ever help ya'll feel free to email me.
06-07-2005, 06:08 PM
You turned the power back on but disconnected the blower motor. Whats to stop the unit from firing compressors on and off? Is there an air proving switch or something?
06-07-2005, 07:49 PM
Can you say frozen coil flooded compressor thats what will happen.
06-07-2005, 10:04 PM
well, none of this sounds very good. I left the power on at the request of the office that monitors the Novar. The unit is a Carrier natural gas furnace and a/c system. Perhaps I should have them shut the power back down to the unit?
06-07-2005, 10:19 PM
Thats a good idea sparky, call them back and have them shut it off. The lower end Carrier units dont have fan
proving or freeze protection. Hell some have no compressor
protection at all. Novar should be fine ignoring that comm
loss untill the units repaired. You dont want a failed
compressor to be blamed on you.
06-07-2005, 10:27 PM
Many of them guys running national accts. have their heads up their ass, there is a reason the hvac guy shut off the unit, maybe they need to contact him about it first.
06-08-2005, 07:14 AM
Wilco, Roger Houston!
I think you hit the nail on the head Diceman! And no, I don't want the HVAC tech cussing me. Thanks again.
06-08-2005, 09:05 PM
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