How to test short in low voltage Y terminal
#1
01-03-15, 11:38 PM
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How to test short in low voltage Y terminal
I have a York Guardian Single Stage Heat Pump, York Electric MV16 Furnace/Air Handler, and a new Honeywell RTH9580 Wi-Fi Smart Thermostat. I got the heat pump installed this past summer.
Recently, the 3A fuse started blowing out of the blue it seems, as the weather has gotten colder. I replaced it with a 5A and it still blew. I can only use Emergency Heat at this time.
As part of troubleshooting, I wanted to just energize "Y" to try and get the heat pump to function. I disconnected EVERYTHING from the air handler terminals (all low voltage wires from the Thermostat and Heat Pump) and started up the fan (by jumping R to G), all good, fan starts. Then if I touch the Y (yellow) wire from the Heat Pump to R... it blows the fuse immediately. I also did it with the C (Common) lines hooked up. I thought there could be a short in my yellow wire to the Heat Pump, so I switched to an unused wire between the AH and HP and it still blew.
Any ideas on why it'd keep blowing? It seems like it could be a short somewhere. Jumping R and Y should work, to test the Heat Pump compressor, right?
Thanks!
Recently, the 3A fuse started blowing out of the blue it seems, as the weather has gotten colder. I replaced it with a 5A and it still blew. I can only use Emergency Heat at this time.
As part of troubleshooting, I wanted to just energize "Y" to try and get the heat pump to function. I disconnected EVERYTHING from the air handler terminals (all low voltage wires from the Thermostat and Heat Pump) and started up the fan (by jumping R to G), all good, fan starts. Then if I touch the Y (yellow) wire from the Heat Pump to R... it blows the fuse immediately. I also did it with the C (Common) lines hooked up. I thought there could be a short in my yellow wire to the Heat Pump, so I switched to an unused wire between the AH and HP and it still blew.
Any ideas on why it'd keep blowing? It seems like it could be a short somewhere. Jumping R and Y should work, to test the Heat Pump compressor, right?
Thanks!
#2
01-04-15, 12:48 AM
Forum Topic Moderator
Turn off the breaker to the outdoor unit and indoor unit.
Disconnect the two 24 volt wires to the contactor and get an ohm reading across the contactor coil.
I'd expect around 12 to 16 ohms.
Disconnect the two 24 volt wires to the contactor and get an ohm reading across the contactor coil.
I'd expect around 12 to 16 ohms.
#3
01-04-15, 12:54 AM
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Did you swap the y wire between the stat and indoor unit or between the indoor unit and outdoor unit?
The latter would be a better test.
Pressure switches are also on the Y circuit. The wire to these pressure switches sometimes rub a short.
The latter would be a better test.
Pressure switches are also on the Y circuit. The wire to these pressure switches sometimes rub a short.
#4
01-04-15, 12:27 PM
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Hey Houston204 -
Thanks for the info... so I tested the resistance across the contactor and it was in the ~16 ohm range, I took a picture linked below in the Heat Pump folder, that shows 17 ohm.
To answer your other question, I tried a different wire for Y from the indoor unit to the outdoor unit (switched from yellow to tan) and it shorted out the same way.
I also disconnected the 24v yellow wire from the outdoor unit entirely (removed wire nut) and tested the voltage across it and it went to zero, so I don't suspect a short in it now.
Another bit of troubleshooting, when I test the V across R and C on the indoor unit, its 27 V. Not sure if thats within the acceptable parameters.
Here are pics of all three of my devices if it helps.
http://bit.ly/1IcRMHW
I appreciate your help.
Thanks for the info... so I tested the resistance across the contactor and it was in the ~16 ohm range, I took a picture linked below in the Heat Pump folder, that shows 17 ohm.
To answer your other question, I tried a different wire for Y from the indoor unit to the outdoor unit (switched from yellow to tan) and it shorted out the same way.
I also disconnected the 24v yellow wire from the outdoor unit entirely (removed wire nut) and tested the voltage across it and it went to zero, so I don't suspect a short in it now.
Another bit of troubleshooting, when I test the V across R and C on the indoor unit, its 27 V. Not sure if thats within the acceptable parameters.
Here are pics of all three of my devices if it helps.
http://bit.ly/1IcRMHW
I appreciate your help.
#5
01-04-15, 01:47 PM
Forum Topic Moderator
I also disconnected the 24v yellow wire from the outdoor unit entirely (removed wire nut) and tested the voltage across it and it went to zero, so I don't suspect a short in it now
Did you check the pressure switch wires for a short?
I would disconnect heat pump Y at the air handler and give the stat a cooling demand to see if the fuse pops.
If it checks out okay, reconnect heat pump Y to the air handler and disconnect Y at the heat pump and give the stat a cooling demand.
If the fuse does not pop it points to a problem inside of the heat pump.
#6
01-04-15, 03:17 PM
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By that I meant, I was testing to see if there was a short (grounded) somewhere along the yellow wire.
So I disconnected the Pressure Switch wires in the outdoor unit, jumpered them, and the compressor comes on now, both for heat and cooling. It's working!
I switched to continuity mode and touched the black wire with one lead, bare metal on the unit with the other lead; got a tone. Did the same with the yellow wire; got a tone. So somewhere along those circuits we must have a short, either bare wire or water I guess. It's odd because this unit is about 6 months old. I am going to search for that now...
Do I have next steps, or at this point, do I need to call the original installer to correct it (hopefully under warranty)? If I need servicing, can I leave the pressure switch circuit jumpered until then (a week)?
So I disconnected the Pressure Switch wires in the outdoor unit, jumpered them, and the compressor comes on now, both for heat and cooling. It's working!
I switched to continuity mode and touched the black wire with one lead, bare metal on the unit with the other lead; got a tone. Did the same with the yellow wire; got a tone. So somewhere along those circuits we must have a short, either bare wire or water I guess. It's odd because this unit is about 6 months old. I am going to search for that now...
Do I have next steps, or at this point, do I need to call the original installer to correct it (hopefully under warranty)? If I need servicing, can I leave the pressure switch circuit jumpered until then (a week)?
#7
01-04-15, 04:05 PM
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You should have at least a 1 year parts and labors warranty.
While I would leave it bypassed, you can void warranty bypassing pressure switches.
While I would leave it bypassed, you can void warranty bypassing pressure switches.
#8
01-04-15, 06:15 PM
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So found the problem -- I popped open the top of my heat pump and looked around and it appeared one of the pressure switch lines got a little too close to one of the copper lines and ended up melting the sheath and shorting it out. I took a picture and posted it.
https://drive.google.com/open?id=0B2...bjA&authuser=0
I moved the wire, retested continuity, no tone. So I put some electrical tape on it, zip tied the the lines (and a couple others) so they'll never touch a copper line, removed the jumper and everything is working again.
Thanks for the help!!
https://drive.google.com/open?id=0B2...bjA&authuser=0
I moved the wire, retested continuity, no tone. So I put some electrical tape on it, zip tied the the lines (and a couple others) so they'll never touch a copper line, removed the jumper and everything is working again.
Thanks for the help!!
#9
01-04-15, 06:40 PM
Forum Topic Moderator
I have seen this happen many times.
I am glad that you were able to locate the short.
The zip ties were a good idea.
I am glad that you were able to locate the short.
The zip ties were a good idea.
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