blown 5amp fuse in air handler

[blazer]

ok,,need some help on this one, i have just installed a bryant 3 ton heat pump and air handler in a town house,(new construction) when i first fired the unit it ran for several hours then blew the 5 amp fuse in the air handler,i checked all my connections and replaced the fuse,,it ran for about two hours then blew the fuse again,,i replaced the stat thinking maybe it was bad,,now the fuse is blowing as soon as i turn power on,,,i pulled the stat ran a wire from the stat up to the air handler bypassing the one in the wall,,when i turned power on display came on at 5 mins air handler came on and at call for outdoor unit it blew the fuse,,so i re mounted the stat and now ran a wire from the air handler out the window down to the heat pump,, units ran for two hours then blew the fuse,,so at this point ive been chasing wires and i cant find a short,,i replaced the defrost board and the board in the air handler,,did then one at a time and both times units ran for two hours each time then blew the fuse !#@$&!$#@*!^%(@!_!+!!!!! dont know what to do next,,,,could it be a short in the reversing valve coil? compressor contactor or in the contactores them selfs ????? cant seem to figure out why im getting a two hour run before it blows,,amp draw on the 24volt power wire never got over 0.16 any ideas????????????

[coolguysfl]

Well - short of gremlins, you've missed something.

Itermittent problems are allways a challenge. You'll need to replicate the fault.

Be sure 1st ALL your connections are 100% correct - do'nt assume it, unwire all the controls & start over.

1) Try in just 1st stage ht
2) Try 2nd stage ht
3) Try cooling
4) Try defrost

[blazer]

thanks,,ive checked all my connections,,i was the first person i blamed,,in fact when i replaced the stat i wired the common and fan backwards((hurry hurry hurry)))) i think tommorow im going to start by disconnecting the reversing valve and seeing how long i can get it to run,,one way or the other it will be the cause or eliminated as the trouble

[backbeatkeeper]

stupid question here Is the transformer tapped for the right voltage?? If its 208 incoming and tapped for 240, you could be getting the wiring to warm up a little and cause some extra resistance, also is tstat wire small gauge? sometimes that and an incorrect tapped transformer can add up to some fun after a few hours of running.

Just a suggestion.....................

[blazer]

thanks backbeat,,i will check into that,,thats a good question,,,trust me at this point ,, i have 30 more of theses to rough in,,i have other jobs to finish and a new 24 unit project starting tomorrow, the more i mess with this to more i fall behind eles where,, im thinking of buying a new unit,, if it solves my troubles great,,tell my factory rep i want a refund if it dont solve my trouble i will use it on the next set,,,, am i lazy ?? or just tired and cold !!!LOL or both or all three

[acg]

yea chech the primary line voltage to transformer and wire in correct tap.you could be having inrushes of too much voltage blowing fuse. (power surge or spike) I recomend the short-pro-tool if locating low volt shorts, in the
meantime install something called the ressetable fuse.
R-270 for a 40va system R-500 for a 75va 24 volt system.

[miami mike]

The fuse is blown as soon as the call for cooling came?

Look at the wires in the condenser.

Look at the wires for the Low?High pressure switches....etc

A wire is probably "skinned" or frayed and touching something.

The unit could be vibrating the wires around during run time......then that "skinned" part of the wire touches a refrigerant line due to the vibration....and pop.

If that wire is now laying on it at start up, it would blow as soon as you put power to it.

That would explain different length`s in run time before the 5 amp fuse blows.


Atleast thats what happened to me last week.(3 moth old equipment)

Pain in the @#$ to find.

[blazer]

thanks for the input ,,i will check into that,,i have traced a bunch of the wires in the outdoor unit and cant seem to find one that is frayed,,thats what got me to wondering if i had a coil heating up,,,i had my amp probe clamed around the 24 volt power wire and it never went over 0.16 while it was running,,

[blazer]

AAHHHHHH!!!!!!!! !!@^!*!!&*!@*@!*@*&**%*%@$*$*!!!! STILL BLOWING AFTER 2 HOURS OF RUN TIME!!!!!!!!!found small burn in defrost wiring thought it might be it,,,and i was wrong!!LOL

[acg]

You said it was new construction right? if you dont think its a power supply problem you must have a intermitent short. Check your ground voltage and locate that short pro tool & reset fuse at Insco. Distributing in Texas...

[Edited by acg on 01-26-2005 at 09:16 PM]

[rango]

Betcha got a shorted contactor coil in the ODU. Check it out and let us know.

[indian]

New construction did you say? Start ohming out your stat wires, sheetrock screws......

[blazer]

yes it is new constr. i have cheked all my wires,,its been running on emer. heat since yesterday afternoon,,the short is in the outdoor unit and at this point ive turned it over to my factory rep,,,ive lost enough time and have other jobs to take care of,so i put it on them,,,the head man is going to check it out and either fix it or replace it,,i have a cool rep,,hes been a great asset to my company in my first year in buss.

[ct2]

Ive seen these guys driving around my neighborhood every now and then in blue vans . They call themselves HVAC professionals. Ill bet they could find the trouble in a jiffy

[baby b]

Blazer,you must check all lv wires individually to ground.Did you try to just jump out system right at A.H.U.?When you ran that new wire out window down to condensor you could of jumped the board out along with condenser wire.

[hvacsteve82]

do you have a battery operated stat or a power stealing stat?

[trane]

I had the same problem on a York heat pump and found wires zip tied on the suction line going to the reversing vave were smashed flat with no wire showing but the insulation was flat and it would short out every couple hours.

[rkious]

Well Try this next time when you have a hard to find short . Take you a box of fuses and several tie in fuse holders . Place a fuse holder in each line going out of the ahu . Make sure the fuse is smaller than the 5 amp fuse and size the fuse for the load that will be on that line . The fuse that blows is were you start tracing back . Then you can place the fuse holder in line a little closer to the load until you find it .
I DO NOT use this until I am way ticked off and lost ( Because of the time it takes ) but it works every time.


Ross Kious

[blazer]

thanks for all the posts,,,have spoken with the head man from my distributor,,he says it sounds like a clasic case of a short in the o circut,,,thinks there is a short in reverseing valve coil,,,he will find out today as ive laid on him as i have to much time vested in finding this short,,, the builder is screaming for a new unit (lol) yeah that will happen !!! can see there point though,,any way,,the big man is gonna try to find it today,,,now he gets to see what i went through the fist two days, the weather today is just as it was when i first fired it up,,,,( 10 degrees with a wind chill of -5) the day i was tracing the short it was 7 degrees with a wind chill of -10,,lol good luck,,,,

[cem-bsee]

with t-stat wire so cheap, just replace that run! that should eleminate that possibility.