Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 03-14-2011, 09:58 PM   #1
Still Learning
 
Join Date: Oct 2009
Location: Los Angeles
Posts: 338
Rewards Points: 0
Share |
Default

Short circuit in secondary wiring


Hey i went to a call today for a system that wouldnt fire up. When i got there i found a blown fuse on the circut board and an error code that said short circut on secondary wiring. I saw that there was a wire going from the common on the circut board to the o/b terminal on the t stat. I disconnected it and the system didnt blow the fuse. My question is why would the system run for 2 months without tripping the fuse? Do you think that cool mode pulls more amps on the secondary?? Cause i replaced the fuse and before removing the wire the system ran in heat mode, bit when i put it to cool mode the fuse popped

thehvacguy is offline   Reply With Quote
Old 03-14-2011, 10:08 PM   #2
AKA HVACTECHFW
 
Join Date: Nov 2010
Location: NE Indiana
Posts: 2,318
Rewards Points: 0
Blog Entries: 1
Default

Short circuit in secondary wiring


O is going to be switched on with cooling, thereby blowing the fuse if it was connected to common

__________________
IT IS WHAT IT IS
hvactech126 is offline   Reply With Quote
Old 03-15-2011, 01:52 AM   #3
Still Learning
 
Join Date: Oct 2009
Location: Los Angeles
Posts: 338
Rewards Points: 0
Default

Short circuit in secondary wiring


I apologise for not clarifying, its not a heat pump, its a natural gas furnace with electric a/c
thehvacguy is offline   Reply With Quote
Old 03-15-2011, 04:39 AM   #4
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,058
Rewards Points: 4
Default

Short circuit in secondary wiring


Quote:
Originally Posted by thehvacguy View Post
I apologise for not clarifying, its not a heat pump, its a natural gas furnace with electric a/c
Many thermostats energize O on a call for cooling weather or not they are set up for a heat pump. So as 126 said, it blew the fuse because the O terminal energized on a cooling call. Some thermostats energize O as soon as the system switch is set to cool, weather or not the thermostat is calling for the A/C to run.

Is the furnace equipped with a VS blower? If so, it may have been miswired in an attempt to control blower speed in cooling mode.
beenthere is online now   Reply With Quote
Old 03-15-2011, 12:44 PM   #5
I'm Your Huckleberry
 
Join Date: Mar 2011
Posts: 5,756
Rewards Points: 0
Default

Short circuit in secondary wiring


Can I ask why would there would be a stat with an o terminal with a wire hooked to it if the system is not a heat pump?
Doc Holliday is offline   Reply With Quote
Old 03-15-2011, 12:45 PM   #6
AKA HVACTECHFW
 
Join Date: Nov 2010
Location: NE Indiana
Posts: 2,318
Rewards Points: 0
Blog Entries: 1
Default

Short circuit in secondary wiring


Quote:
Originally Posted by Doc Holliday View Post
Can I ask why would there would be a stat with an o terminal with a wire hooked to it if the system is not a heat pump?
because it was not wired properly from the beginning
__________________
IT IS WHAT IT IS
hvactech126 is offline   Reply With Quote
Old 03-15-2011, 12:50 PM   #7
Member
 
hvaclover's Avatar
 
Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Rewards Points: 0
Default

Short circuit in secondary wiring


Quote:
Originally Posted by Doc Holliday View Post
Can I ask why would there would be a stat with an o terminal with a wire hooked to it if the system is not a heat pump?

The O terminal is an accessory connection. Some stats have them in heat and cool.
__________________
Just slow, not stupid.
hvaclover is offline   Reply With Quote
Old 03-15-2011, 12:58 PM   #8
Still Learning
 
Join Date: Oct 2009
Location: Los Angeles
Posts: 338
Rewards Points: 0
Default

Short circuit in secondary wiring


Quote:
Originally Posted by beenthere
Is the furnace equipped with a VS blower? If so, it may have been miswired in an attempt to control blower speed in cooling mode.
Um, to the best of my knowledge all furnaces in my region have vs motors in them. Usually low speed is for heat, high is for fan, and med/low is cool. If you meant to say two stage then no, its a single stage system.
thehvacguy is offline   Reply With Quote
Old 03-15-2011, 01:00 PM   #9
Still Learning
 
Join Date: Oct 2009
Location: Los Angeles
Posts: 338
Rewards Points: 0
Default

Short circuit in secondary wiring


Quote:
Originally Posted by Doc Holliday
Can I ask why would there would be a stat with an o terminal with a wire hooked to it if the system is not a heat pump?
Haha because the homeowner wanted to save money by replacing the thermostat himself. Thats fine by me cause i made more money off of him fixing the problem
thehvacguy is offline   Reply With Quote
Old 03-15-2011, 01:05 PM   #10
Member
 
hvaclover's Avatar
 
Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Rewards Points: 0
Default

Short circuit in secondary wiring


Quote:
Originally Posted by thehvacguy View Post
Um, to the best of my knowledge all furnaces in my region have vs motors in them. Usually low speed is for heat, high is for fan, and med/low is cool. If you meant to say two stage then no, its a single stage system.
Hey Surfer Boy, you are a describing a PSC multiple speed motor.

Variable speed would be an ECM half have D.C. motor.

Lay off the medical grass dude.
__________________
Just slow, not stupid.
hvaclover is offline   Reply With Quote
The Following User Says Thank You to hvaclover For This Useful Post:
hvactech126 (03-15-2011)
Old 03-15-2011, 02:30 PM   #11
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,058
Rewards Points: 4
Default

Short circuit in secondary wiring


Quote:
Originally Posted by Doc Holliday View Post
Can I ask why would there would be a stat with an o terminal with a wire hooked to it if the system is not a heat pump?
VS systems often need power to the O terminal for the blower slow down for enhanced dehumidification ability.
beenthere is online now   Reply With Quote
Old 03-15-2011, 02:39 PM   #12
Member
 
hvaclover's Avatar
 
Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Rewards Points: 0
Default

Short circuit in secondary wiring


Quote:
Originally Posted by beenthere View Post
VS systems often need power to the O terminal for the blower slow down for enhanced dehumidification ability.
Are you stating that as the reason that the fuse blew?
__________________
Just slow, not stupid.
hvaclover is offline   Reply With Quote
Old 03-15-2011, 02:48 PM   #13
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,058
Rewards Points: 4
Default

Short circuit in secondary wiring


Quote:
Originally Posted by hvaclover View Post
Are you stating that as the reason that the fuse blew?

The fuse did blow because the O energized and was connected to the common at the board.

I posted what the may have been thinking or trying to accomplish when they connected the O terminal.

Heck, they may have thought the O was the C terminal.
beenthere is online now   Reply With Quote
Old 03-15-2011, 03:02 PM   #14
Member
 
hvaclover's Avatar
 
Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Rewards Points: 0
Default

Short circuit in secondary wiring


Quote:
Originally Posted by beenthere View Post
The fuse did blow because the O energized and was connected to the common at the board.

I posted what the may have been thinking or trying to accomplish when they connected the O terminal.

Heck, they may have thought the O was the C terminal.
Just checking. It was obvious that a hot 24v going back to a neutral common would blow a fuse.

Your response (at least to me) was not clear in that regard.
Thank you for clarifying,
__________________
Just slow, not stupid.
hvaclover is offline   Reply With Quote
Old 03-15-2011, 05:40 PM   #15
Still Learning
 
Join Date: Oct 2009
Location: Los Angeles
Posts: 338
Rewards Points: 0
Default

Short circuit in secondary wiring


Quote:
Originally Posted by hvaclover

Hey Surfer Boy, you are a describing a PSC multiple speed motor.

Variable speed would be an ECM half have D.C. motor.

Lay off the medical grass dude.
You dont have to be a dick im only 23 i have years of experience in front of me. And by the way, just because i live in la doesnt mean i surf and smoke pot. Actually i dont even skateboard. I build homes

thehvacguy is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Need a wiring diagram Mooreski Electrical 46 03-12-2011 03:25 PM
Wiring Help, Changing a Dryer and/or Stove circuit to something else shunut Electrical 10 01-08-2011 03:06 PM
short circuit question bryan1282 Electrical 1 10-05-2009 05:14 PM
Wiring a single pole switch into a 220v circuit rlmorgan Electrical 38 10-15-2008 07:59 PM
wiring a gfci outlet in circuit bobo Electrical 12 08-31-2005 08:38 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.