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 01-25-2012, 09:43 AM   #1
Newbie
 
Join Date: Jan 2012
Posts: 16
Share |
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


Dear fellow DIY techs,

I have a Bryant FA4BNF024 HVAC handler that blows the 5 amp low voltage fuse intermittently. Last time it blew, was May of last year. Now it has blown again. I replaced the fuse yesterday morning and it took a whole day to blow again. I have a degree in electronics and am home for the next week, so I thought I'd try and tackle this situation. Now, by observing the fuse itself, it is definitely a high current situation...no metal fatigue or slight over-current. The fuse is blown black..wide open. I Google'd the model number and found this handler has been sold under MANY names...thankfully I found the service manual. I placed a fused jumper in place of the fuse and a current probe, then waited to see if I could isolate the problem area. Wouldn't you know it....3 hours and no-blow. I ran the thermostat up to 90 to make the aux heat turn on..still nothing (yes, I have a heat pump..sorry did not say initially). Now, my Totaline touch-screen programable thermostat for the unit has been flakey in the past..goes blank, resets..even blacks out sometimes when removing the bezel. However, I cannot get ti to act up now. My thoughts were maybe the thermostat was blowing the fuse. I checked all wiring outside at compressor unit and at thermostat...no nicks, rubs or bare wiring.

Any guidance as to how to split the circuit, maybe install more fused wiring in each leg until I can determine for a fact what area or component is bad?

Last time it blew in May, I was deployed to Iraq...the young service tech my wife called just replaced the fuse and last..no testing. What I don;t want is someone coming out and "shooting from the hip" with my $$$. So, that is why I am attempting this....plus..it gives me a chance to learn how the control side of home HVAC works.

Thanks in advance,

Doug

ArmyChief is offline   Reply With Quote
Old 01-25-2012, 10:15 AM   #2
Member
 
biggles's Avatar
 
Join Date: Jan 2008
Location: Long Island
Posts: 3,621
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


focus on the items that have coils within them... definitly that compressor contactor outside in the condenser and the run out of the stat wires from the TR in the air handler.if your reversing valve is also 24Vs out there that and the contacor are the loads pulling on the TR thru that fuse.question.did you upgrade the present stat with the exsisting transformer typical is 40VA-50VA as installed? does the air handler have a control board in it,does the elctric backuo heat have a relay these are all loads.the sta won't blow the fuse or it would never control what the stat is calling in either heat or cool is the hit.might want to install a mini circuit breaker on the TR-R hot to replace the fuse.wire run outs like stat wire to the condenser draw on that VA from the TR.when they first close there is a amp spike but for milli seconds.shut the disconnect outside on the condenser and check the action of the contactor should be free in/out ny hang up it will blow a fuse trying to close....spritz a little WD40 on the slide bar ...but definitly consider a 3A-5A CB,or an upgrade on the TR to 60VA(if stat was upgraded) with a CB mounted on the 24V side #3TZ69 at local Grainger

biggles is offline   Reply With Quote
The Following User Says Thank You to biggles For This Useful Post:
ArmyChief (01-25-2012)
Old 01-25-2012, 10:30 AM   #3
Newbie
 
Join Date: Jan 2012
Posts: 16
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


Biggles,

Thanks for the quick reply. The handler and thermostat, one on wall or course, are original with the house..approx 2006. So, I can go look at transformer (what you call TR I think)..to see if it is marked with VA rating.

Air handler does have control board. Thermostat is not battery operated Nd is powered from the 24 VAC from transformer..through the control board which has the 5 amp fuse on it.

I've read contactors typically go bad in that the silver wears off and the metal fuses together...causing compressor to run all the time. I do know e outside unit comes on and off. With that and aux hear..I measured no more than 1 amp...even with glitch detect on. Like I said above...this fuse, when it blows...it is obliterated inside...burnt black.

I have stripped back the low voltage wiring outside going into the compressor assembly. Can I install a fuse in one of those wires to determine if a component (not sure what components inside the compressor/fan assembly outside draw from the 24 VAC). I see what appears to be a pressure transducer on the discharge line, a startup capacitor..what does the contactor look like?...what end item would it be connected too? I do not understand the WD40 reference..can you expand what it is testing and why?

I don't care how long it takes, since this is a upstairs unit, currently not occupied...I just want a good diagnosis and repair

Thanks again
ArmyChief is offline   Reply With Quote
Old 01-25-2012, 12:54 PM   #4
HVAC Tech/ Browns Fan
 
Join Date: Dec 2009
Location: Dayton, ohio
Posts: 541
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


You may have a bad t-stat. If you are 100% not seeing any chew up wire's then replace t-stat. I will start from there first. P.s. thank you for serving us over sea keeping us all safe here in the great U.S.A!!!!!!
Tator1076 is offline   Reply With Quote
Old 01-25-2012, 01:02 PM   #5
HVAC Tech/Owner
 
Join Date: Nov 2010
Location: VA
Posts: 436
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


I had an FA4B that I had the same problem with.....could not find a short in any of the wires, or circuit boards or defrost boards.....The only thing I could find wrong was there was never a ground wire run to airhandler. I ran the ground wire to the airhandler and have never had another fuse blow......
Technow is offline   Reply With Quote
Old 01-25-2012, 01:07 PM   #6
Member
 
biggles's Avatar
 
Join Date: Jan 2008
Location: Long Island
Posts: 3,621
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


the WD40 refeence was to give the contactor within the condenser a shot right on the pull in on the contactor.the compressor and fan are on the same contactor.the low pressure maybe hi side have sensors on them with wires that is all 24Vs either breaks the compressor when running in heat or cooling...TR is the transformer just didn't want to type it out... good point on the solder breaking down over the years even vibration from the fan.see those black relays on the control board they are your relays with 24V coils within.fusing the condenser isn't going to help you need it right at the TR as you have.the board is probably the biggest VA(voltamps) draw on that TR and it should have a VA rating on the TR tag.that nuke of the fuse is sounding like a dead short,and not a load break could be a wire rub out R (HOT) to metal.the trick is to get a routine going and slowly eliminate items..check the back of the control module for discolered and or the resister on the relay side.biggy there also is the reversing valve if it is 24Vs?..did you notice a TR in the condenser.the biggest give away if your blowing fuses in heating and cooling seasons either something in the condenser or the stat wire run going out there.keep this site http://www.bestbuyheatingandairconditioning.com/ handy and local Grainger for items
biggles is offline   Reply With Quote
Old 01-25-2012, 01:19 PM   #7
Part of the Clover Leaf
 
Join Date: May 2011
Location: NW Burbs of Detroit Mi.
Posts: 1,107
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


My two cents FWIW, cheek all low voltage wiring for the the slightest chafe.

I have found chaffing where conductors pass thru the wall. They can also be harder than the dickens to locate on conductors that are in the open.

like trying to trace the wiring diagram on an Army ANGRC/26Delta
hvac5646 is offline   Reply With Quote
Old 01-25-2012, 01:23 PM   #8
Newbie
 
Join Date: Jan 2012
Posts: 16
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


@tator
I'm still thinking possible T-Stat...however, don't like guessing. Will keep it on the plausible list

@biggles
Where is the reversing valve and what does it look like? Is it a electromechanical device...you say operated with the 24 VAC...by a relay?

Since there is a fuse on control board which is in series with SEC2 winding of Transformer...why can I not isolate the 24 VAC going out side to determine if issue is in handler to T-Stat or handler to outside unit?

Thanks again everyone
ArmyChief is offline   Reply With Quote
Old 01-25-2012, 01:49 PM   #9
Member
 
biggles's Avatar
 
Join Date: Jan 2008
Location: Long Island
Posts: 3,621
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


the 24V going outside might not exsist if there is a TR within the condenser...goggle reversing valve for pix or youtube it.reversing valve swings the discharge superheated freon from the condenser outside to the indoor air handler coil that force is coil controlled from the stat check this youtube...

Last edited by biggles; 01-25-2012 at 01:52 PM.
biggles is offline   Reply With Quote
Old 01-25-2012, 05:16 PM   #10
HVAC Tech/ Browns Fan
 
Join Date: Dec 2009
Location: Dayton, ohio
Posts: 541
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


Is it running fine in Emergency heat?
Tator1076 is offline   Reply With Quote
Old 01-25-2012, 05:18 PM   #11
HVAC Tech/ Browns Fan
 
Join Date: Dec 2009
Location: Dayton, ohio
Posts: 541
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


FYI you can get a t-stat from lowes and if don't work you can always take it back.
Tator1076 is offline   Reply With Quote
Old 01-25-2012, 05:32 PM   #12
Newbie
 
Join Date: Jan 2012
Posts: 16
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


Emergency heat works fine..and it has not blown all day

Luckily this is not the main unit...so time will tell.

Thanks,
ArmyChief is offline   Reply With Quote
Old 01-25-2012, 06:31 PM   #13
Part of the Clover Leaf
 
Join Date: May 2011
Location: NW Burbs of Detroit Mi.
Posts: 1,107
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


TIME TO CALL IN THE BIG GUNS....
hvac5646 is offline   Reply With Quote
Old 01-25-2012, 06:36 PM   #14
Newbie
 
Join Date: Jan 2012
Posts: 16
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


Nah...you guys would fix the problem...but there'd be nothing left of the house when you were done !..lol
ArmyChief is offline   Reply With Quote
Old 01-25-2012, 07:04 PM   #15
HVAC Tech/ Browns Fan
 
Join Date: Dec 2009
Location: Dayton, ohio
Posts: 541
Default

FA4BNF024 HVAC Unit - Blows 5 amp low voltage fuse intermitently


Do you have a humidifier on this system? I still go with replace t-stat. Did you check t-stat from indoor unit to outdoor unit because I did find other day another company cable tie the t stat wire to bare suction line and wires had melted to cooper over time causing the short. Note did you had new siding put on the house maybe a nail hit it. But most case that will be 100% short

Tator1076 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 help determining the size of an upstairs HVAC unit BigE516 HVAC 11 03-17-2009 03:25 PM
new hvac precharged unit install reno1011998 HVAC 1 01-30-2009 02:37 PM
HVAC unit moves too much air - can I slow the fan down? UtahGuy HVAC 7 12-16-2008 06:06 PM
does this sound like a broken/hurting hvac unit? joeyboy HVAC 3 06-28-2008 10:44 AM
Space around the HVAC unit? QueenL HVAC 8 04-16-2008 12:50 PM




Top of Page | View New Posts

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