no power to tstat

Reply

  #1  
Old 07-06-14, 03:27 AM
Member
Thread Starter
Join Date: Jul 2014
Posts: 11
Received 0 Votes on 0 Posts
no power to tstat

My A/C unit and attic air handler would not come on, no power to tstat, found out there was a dead chipmonk laying on top of contactor, when I depressed the contactor both compressor and fan motor would come on, yet air handler would not. Checked all breakers, reset the air handler switch, nothing !
 
Sponsored Links
  #2  
Old 07-06-14, 04:29 AM
Member
Join Date: Jun 2008
Location: VA.
Posts: 813
Received 1 Vote on 1 Post
Check inside the air handler for a blown fuse coming off the control transformer. It may be an inline fuse or on a little circuit board.
If it's a blown fuse, I would check to make sure chip monkey didn't chew some wires up in the condenser.

Edit: Be sure to disconnect power before going inside.
 
  #3  
Old 07-06-14, 04:29 AM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,470
Received 11 Votes on 8 Posts
Check around the air handler for a fuse for the 24VAC transformer. It's often a 3 amp fuse. It protects the transformer should a short occur. If you can't find a fuse, check the output of the transformer (usually located in or near the air handler) for 24VAC. If present, then you'll have to check the wiring to find out where it's being lost.
 
  #4  
Old 07-06-14, 10:16 AM
Member
Thread Starter
Join Date: Jul 2014
Posts: 11
Received 0 Votes on 0 Posts
I don't recall seeing any auto like inline fuse near the attic air handler, the transformer has a reset button though, I reset it a few times, nothing happened. The purpose of the reset button is to protect the transformer, right ? If that is the case, the transformer should be ok ? I'll check the output from transformer next time I go up, it's too hot now. BTW, since the A/C compressor and fan motor came on when I depressed the contector, does it mean all breakers are good ?
 
  #5  
Old 07-06-14, 10:23 AM
Member
Join Date: Sep 2008
Location: Long Island
Posts: 769
Received 0 Votes on 0 Posts
pute stat to fan ON if it runs the tr is good if it doesn't TR might be shot...remove 115V primary pair and 24V secondary pair on the tr and ring them each pair seperate out not looking for resistance just continuity.if you have 115V into the TR standing you should have 24V at the nearest readable point in the air handler
 
  #6  
Old 07-06-14, 10:42 AM
Member
Thread Starter
Join Date: Jul 2014
Posts: 11
Received 0 Votes on 0 Posts
I did put fan on from tstat, nothing happened, no noise from air handler, no power at tstat. Too bad it is so hot up there now, can't do anything. Questions:
1. if no 115V standing going into TR -- what problem ?
2. I didn't see circuit board in air handler -- possible ?
Clarification: chipmonk was on A/C contactor, not in air handler.
Thanks for your reply
 
  #7  
Old 07-06-14, 11:04 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 52,627
Received 339 Votes on 317 Posts
Welcome to the forums.

A make and model of your air handler would be really helpful.
 
  #8  
Old 07-06-14, 11:09 AM
Member
Thread Starter
Join Date: Jul 2014
Posts: 11
Received 0 Votes on 0 Posts
A/C : Lennox HS22-461U-2P
Air handler: Lennox CBH19-41-2P
 
  #9  
Old 07-06-14, 12:31 PM
Member
Join Date: Apr 2007
Posts: 14
Received 0 Votes on 0 Posts
You'll have to pull the cover off of the air handler to get to the circuit board and fuse. It may be that your air handler will have 2 covers. The one you want to remove is where the electrical wiring enters the air handler. You probably should kill the power (by flipping the breaker off at your electrical service panel) before you remove the cover.
 
  #10  
Old 07-06-14, 12:57 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 52,627
Received 339 Votes on 317 Posts
I've left a link to your manual below. On page 4 it shows two fusing methods. Yours may be a fuse holder on the transformer.... not a reset button.

Hvac parts shop manuals FCB19 20Series.pdf
 
  #11  
Old 07-06-14, 01:47 PM
Member
Thread Starter
Join Date: Jul 2014
Posts: 11
Received 0 Votes on 0 Posts
PJmax, after seeing the schematic, I am glad there is still hope I can do something about it, no wonder the "reset button" felt kind of stiff.
Now let me try to remove the fuse and hope the problem is solved !
Thank you kindly for your time and effort ! much appreciated !
 
  #12  
Old 07-06-14, 04:04 PM
Member
Thread Starter
Join Date: Jul 2014
Posts: 11
Received 0 Votes on 0 Posts
Went up there in the oven and got the fuse out, sure enough, it was wasted.
I tried radio schack and Sears with no luck, got on Grainger online, couldn't find one, now searching electronic stores nearby online.
Buss fuse w/ 2 flares at one end, 125V, 3.5A, 3.5mm.
 
  #13  
Old 07-06-14, 05:28 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 52,627
Received 339 Votes on 317 Posts
Is there a part number on it ?
 
  #14  
Old 07-06-14, 05:53 PM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 7,372
Received 10 Votes on 8 Posts
Have you looked at the 1CK54 at Grainger?
http://i151.photobucket.com/albums/s...seTraneAHU.jpg
 
  #15  
Old 07-06-14, 06:59 PM
Member
Thread Starter
Join Date: Jul 2014
Posts: 11
Received 0 Votes on 0 Posts
no, it only says buss 125V on one end, 3.5A on the other
 
  #16  
Old 07-06-14, 07:16 PM
Member
Thread Starter
Join Date: Jul 2014
Posts: 11
Received 0 Votes on 0 Posts
Thanks for checking Houston, it doesn't have a retainer cap. One end of the fuse is half mm longer and the metal part has a flare on opposite sides. The cavity for the fuse has 2 slits which will accept the flares of the fuse, when you push in the fuse and twist the flares will prevent it from backing out. The end of the fuse sticking out will fool you into thinking it is a reset button.
 
  #17  
Old 07-06-14, 07:38 PM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 7,372
Received 10 Votes on 8 Posts
  #18  
Old 07-06-14, 08:01 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 52,627
Received 339 Votes on 317 Posts
Wow... $5 a fuse. No one bashful there.
 
  #19  
Old 07-06-14, 08:31 PM
Member
Thread Starter
Join Date: Jul 2014
Posts: 11
Received 0 Votes on 0 Posts
That's it ! It looks exactly like that, thank you very much for your time, Houston.
Would also like to thank everyone here for you suggestion, been a great help !
 
  #20  
Old 07-06-14, 09:17 PM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 7,372
Received 10 Votes on 8 Posts
I would verify that the contactor coil is ~ 12 ohms or more before installing the new fuse.

3 ohms or less is shorted and will pop another fuse.
 
  #21  
Old 07-07-14, 05:03 AM
Member
Thread Starter
Join Date: Jul 2014
Posts: 11
Received 0 Votes on 0 Posts
You mean the air handler ? ok I'll check it , thanks again.
 
  #22  
Old 07-07-14, 05:06 AM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 7,372
Received 10 Votes on 8 Posts
If a critter shorted the contactor by crawling across it the contactor coil is probably toast.

If it reads less than 3 ohms it requires replacement.
 
  #23  
Old 07-07-14, 05:53 AM
Member
Thread Starter
Join Date: Jul 2014
Posts: 11
Received 0 Votes on 0 Posts
thanks for the clarification
 
Reply

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


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: