I have a short in the low volage circuit in my Trane HVAC system.

The ceramic fuse pops when I turn the AC or the heat on.

If I just turn on the Blower motor in manual mode and leave ac and heat in the off position, the fan blows at low speed with no problem.

As soon as I turn on heat or a/c the blower motor speed increases and then in about 15 seconds the fuse blows.

I have visually checked as many wires as I can and I do not see any shorts. Any ideas.

Kind Regards,
Joe

More info needed,

https://www.askmehelpdesk.com/heating-air-conditioning/read-heating-air-conditioning-faq-hvac1000-284131.html

The Airhandler is a ;

Trane Model# TWE031E13FA1
Manufacture Date 3/96
The Outside Unit is a

Trane Model# XL1400
SUPER EFFICIENT HEAT PUMP
Model # TWY018A100A3

The Airhandler is a ;

Trane Model# TWE031E13FA1
Manufacture Date 3/96
The Outside Unit is a

Trane Model# XL1400
SUPER EFFICIENT HEAT PUMP
Model # TWY018A100A3

That is a standard unit as far as wiring is concerned but it does have a variable speed motor.

As with all short circuits the removal of a wire to a component can help track it down. What you might do is to sub the ceramic fuse for something cheaper to do your testing with. I have a 1-2 3-4-5 amp mini circuit breakers I use for testing purposes so I do not have to keep replacing the fuse.

Many of the variable speed setups do use a signal from the low voltage section of the circuit board. When you say it pops after about 15 seconds that gives whatever is overloading enough time to cause enough draw on the low volt side to pop the fuse. Since the fuse does not go right away this could be a tuff one to figure out. The circuit board also might have a built in time delay and that would allow for the 15 seconds also.

Outside unit

http://hvactroubleshooters.com/TRANE/2TWX4030B1000A%20HEATPUMP%20SERVICE.pdf

inside

http://www.aireng.com/clientuploads/Coils_etc/twe_e.pdf

I hope these manuals help you find and track down the problem.

Thanks for the manuals.
Would a short in any of the components, relays, or fan be the cause for the overload or should the problem only be in the low voltage wiring?

Thanks for the manuals.
Would a short in any of the components, relays, or fan be the cause for the overload or should the problem only be in the low voltage wiring?


Anything that has to do with low voltage should be your target. As I said before some variable speed motors have low voltage used with them als. See attached.

So based on what I have seen and what you have told me, a bad blower and or a shorted wire to the blower motor could overload the low voltage circuit. Right?

Yes that is a possibility BUT there are other items that could also cause the problem. I was just making you aware of the motor situation. I would isolate the low voltage wires one circuit at a time till the problem is found.
You could also have a short in one of the low voltage wires going to the outside unit. Sometimes a dog or other animal will chew on those wires outside. You have many items to check/test.

Ok I have put a short tester on the system and the circuit keeps breaking. I have disconnected the blower and the breaker keeps popping. I am now ready to start disconnecting low voltage wires one at a time to see which wire must have a short. I have the following wires from the thermostat to the air handler, and then out ot the outside unit.

These are my wires
B- Blue
W- White
R - Red
T - Brown
Y - Yellow
G - Green
O - Orange
X2 - Black

Is there any particular order you would recommend disconnecting them and testing them?

One more question.

Do you have a description for these different letters?

B- Blue
W- White
R - Red
T - Brown
Y - Yellow
G - Green
O - Orange
X2 - Black

I am trying to change out the old thermostat
and it just has the following letters on it.
Can you show me which one of the above letters coorelate with the ones below?

Rc/R = 24VAC power supply
C = 24vac Common
Y1 = Compressor Stage1
Y2 = Compressor Stage 2
W2 = Auxiliary Heat
E = Emergency
O = Cool Mode Powered Reverse Valve
B = Heat mode powered reverse valve
G = Fan
L = System monitor

Have you tried operating the system in the emergency mode? If the fuse does not blow, your problem is definitely in one of the control circuits to the outdoor unit. Check the contactor(s) and reversing valve at the heat pump for evidence of burned coils.

You are the on site professional. I have supplied you with all the info I have. Since I am not there I cannot do the testing for you or offer you comments on your ability. As I always tell people. It is your equipment and you are working on it. It is difficult if not impossible to be a back seat driver under these circumstances since I want no responsibility if damages occur.

I have isolated the short to the yellow wire which goes from the airhandler to the outside unit.

It is on the Y circuit and it is called the "1st stage compressor wire"

Any thoughts?

Yep that is the control wire for the comperssor/fan contactor outside. Could be the coil is shorted. OR other items in the Y control wire circuit.

I am close guys.

I traced the yellow wire at the outside unit and I noticed that the yellow wire goes to the side of the MS (look like the contact points). In the schematic however the yellow wire goes to the printed circuit board of the outside unit. Is this an option or an alternative way of wiring the system?

The MS stands for the "compressor motor contactor".

If yer pokin' 'round the outdoor unit, you betta pull out the disconnect or shut off the breaker.
If you have an ohm meter, check the contactor coil with the wires disconnected. Low or no resistance will blow that fuse. See if da coil looks burnt.

Ok I tested the resistance across the coil with the wires connected.

There was 1.8 M Ohms. This is low resistance I believe. Do you know what its resistance should be?

Ok I tested the resistance across the coil withthe wires connected.

There was 1.8 M Ohms. This is low resistance I believe. Do you know what its resistance should be?

You need to disconnect the wires to the contactor coil to check it's resistance. The wires being connected will give you a false reading.

I just remove the wires. One from each side of the coil. The reading was 1.2 M Ohms.

What does everyone think?

Just apply 24 volts to it. If it slams shut you know it is working and not fried. If the leads spark a lot when you touch the 24 volts to it then you know it is toast.

fljrc3:

Flrjc3: try removing the y wire first which will isolate ouside low voltage. The condenser unit has low voltage board for condenser fan which I have seen short out.

I have a couple of questions for you if you please. First I assume that you have a furnace with a hot surface ignitor? And next have you ever noticed a test post on the circuit board?

With the low voltage fuse blowing it has to have ssomething to do with the low voltage lines of cor coils.

If I were you I would disconnect the Red, White. Green and yello wires form the low voltage terminals on the circuit board.
Next I would jumper from the red to the white, hold this about the length of time that it takes for the fuse to blow. If it does blow notice if the hot surface ignitor glowed at all. Also diod the inducer motor on the vent come on and run

If this has not told you any thing I would suggest putting the wires back in place and then try to find the test terminal and follow the instructions on how to use it and see if it will go all the way through the cycle. Notice it will not turn on the gas in the test.

I hope this helps

The original poster hasn't updated this in over a week. Bringing up old/dead threads is rather pointless as your answers usually fall on deaf ears.

Don't jump to conclusions guys... maybe his internet service is really, really sloooooooow...

Don't you have a variable speed motor to be fondling?

You call it fondling, I call it Saturday night!

It's only Wednesday. Don't tire yourself out.

Wednesday? No wonder she's not home.

Knowing VS motors it probably broke down halfway home and can't afford to make it the rest of the way.

Witty... you are proving to be a most worthy adversary for VSM

Hi Guys,

Everybody relax. I haven't responded because the weather has been good here in Florida and my wife hasn't forced me up into my little crawl space of an attic to finish working on the HVAC system.

I finally finished this project on Sunday afternoon just prior to the football games.

I pulled one low voltage wire at a time off the printed circuit board at the air handler.

I attached a circuit tester across the low voltage fuse wiring and contiued removing one wire at a time until the short went away. As I mentioned before it was the yellow wire that went to the contactor coil that stop triggering the circuit breaker. I replaced the contactor and the short went away and the system works great.

In addition I replaced the Trane mercury switch thermostat controller with a Lighted Hunter LCD touch screen display. The system works like a new cadillac now.

Thank you all for your support and guidance. You saved me a lot of money, and I got a great education in the process.

Joe C.

I knew it all along. It's a gift. Your welcome. 4-11-26-32-38-49.