Does anyone use a low voltage short tool? Or is the preferred method just using your volt meter? What kind if tool is the best?
Low voltage short tool
Aronsx
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Yes, just so the transformer doesn't burn up while finding the short. I know you can use a in line fuse on the secondary and amp probe on it to see if it's drawing. I just was wondering if anyone uses them and is any of them better.
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14,568 Posts
I use an old analogue amp meter. The needle jumps instantly on a low voltage short instead of waiting for a digital to read out. Go to the AH and jump each control wire one at a time until you see the meter jump and you've found the problem wire or control. A lot of the newer units have TD's on the condenser board which makes it a little more difficult if it's the contactor coil. Intermittent shorts are a whole other problem.
I dont follow, what are you saying to do?
Just realized this isn't the pro side, better not give any "dangerous" info out
My preferred tool is two 12v automotive brake bulbs in series. There are two different wattage filaments in one bulb and arranged just like a compressor. Common, dim, and bright. Go to a junk yard and get two brake light bulb holders, then shop the bulbs to fit them.
The pair will glow like you put them across the transformer when there's a short. You could also use this as a load and snag on wires. It will flicker when you disturb a loose connection.
You have to use two in series, because HVAC is 24v. Aircraft 28v bulbs are better for this, but they're not as readily available.
If you wire the two dimmer filaments together, you'll pull 15VA or so. Bright filaments about 40VA or full load. The dim filaments in series will only pulls about 0.5A on a short but most loads won't work correctly when it is in line.
If you wire for the brighter filament, it will glow brighter and get much hotter. Many lighter loads will actually run fine with bulbs in series, because the resistance of filament is quite low when it is cold. The only problem is that it will draw the full 40VA all day long and this can burn out the relay or the anticipator in the thermostat.
Another method is using multiple fuses at the air handler. if 24v is used to operate dampers or other devices, this may not apply.
5A fuse for R.
1A for C. C is only used for powering the thermostat.
2A fuse for each one of the wire AT THE AHU side. W,Y,G,W2..... These lines are shorted to R in thermostat to control.
If only the 5A R fuse melts, one of the wires are grounding to a metal building part. If only one of the control input (i.e. Y or W), melts, it is probably the components such as gas valve having intermittent issues or wiring within AHU.
If the 1A fuse on C melts, one of the wires are shorted to C.
5A fuse for R.
1A for C. C is only used for powering the thermostat.
2A fuse for each one of the wire AT THE AHU side. W,Y,G,W2..... These lines are shorted to R in thermostat to control.
If only the 5A R fuse melts, one of the wires are grounding to a metal building part. If only one of the control input (i.e. Y or W), melts, it is probably the components such as gas valve having intermittent issues or wiring within AHU.
If the 1A fuse on C melts, one of the wires are shorted to C.
This is where a Zebra Stat comes in handy, use W1 for a 3 amp protection that auto resets.
The
white test lead is protected with a 3 Amp device.
You can learn more about its use in the
“Troubleshooting Electronic Boards” section.
The second device provides an overall protection
for the ZebraStat. It is rated at approximately
5 Amps at 28 Volts. (150VA)
If you inadvertantly hook up the ZebraStat’s
power input leads using an incorrect ‘polarity’
and attempt to use the Activation Mode, or if
you allow a loose ‘hot’ lead to touch ground,
you will probably ‘trip’ this circuit protection,
shutting down the ZebraStat, and turning on
the red TRIP LED. The unit will remain in the
tripped condition until you remove all power
to the unit for about 15 seconds. Before reconnecting,
discover and correct the condition
that caused the trip in the first place.
This protection device is not meant to protect
the unit from higher voltages than 28 Volts.
The
white test lead is protected with a 3 Amp device.
You can learn more about its use in the
“Troubleshooting Electronic Boards” section.
The second device provides an overall protection
for the ZebraStat. It is rated at approximately
5 Amps at 28 Volts. (150VA)
If you inadvertantly hook up the ZebraStat’s
power input leads using an incorrect ‘polarity’
and attempt to use the Activation Mode, or if
you allow a loose ‘hot’ lead to touch ground,
you will probably ‘trip’ this circuit protection,
shutting down the ZebraStat, and turning on
the red TRIP LED. The unit will remain in the
tripped condition until you remove all power
to the unit for about 15 seconds. Before reconnecting,
discover and correct the condition
that caused the trip in the first place.
This protection device is not meant to protect
the unit from higher voltages than 28 Volts.
From Autozone works good also. Lisle 3 to 28 volt lighted stick tester.
- Indicates polarity
- Won't damage sensitive electronic components
- Draws less than 21mA at 12 volts DC
- Operating range 3-28 volts
- The red light indicates positive polarity, green indicates negative polarity
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3,004 Posts
I have both as well, and use only short pro now
I like Ican answer and the zebra tool. Where can you get a zebra tool? I looked on AMAZON. I also looked at autozone in the fuse section for the tester, I didn't see a tester but I think I saw the spot where they were but were sold out. I like everyone's input. Anyone else have a different way?
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