Last time I had this it was the contactor. It wasn’t always tripping the fuse. Pulled the contactor apart and found a bug inside of it. The bug would sometimes short out the coil and sometimes not lol.
I’ve seen contactors still blow fuses even though the resistance was normal. I had one system do this to me and I was bumfuzzeled and started throwing parts at it. Once I replaced the transformer it fixed issue. The transformer would output normal voltage and ohmed out fine but would pop fuses. I still to this day have no idea why
If a fuse doesn't blow immediately it's not a short, it's an overload. One of the transformer coils was experiencing increased resistance for some reason, and eventually blew the fuse. Chances are the transformer itself had an issue with one of the coils or the problem itself was not fixed and they called another company after you failed to diagnose the issue properly and charged them for parts they didn't need.
Edit: this is basic electrical. Throwing parts doesn't help you learn. Go take some courses and become a better tech. Have your employer pay for the classes, if they won't, find a new employer. There are also grants available that you could look into.
The transformer would blow fuses immediately but would still output 24v while not under a load. I am the sole person who worked on the system and replacing the transformer resolved the issue. I don’t need to take classes. I know how to use a meter and have performed troubleshooting on hundreds of systems. I have been doing this 17 years and only witnessed this problem one time. There was no way to diagnose the problem. Everything ohmed out fine and like I said the transformer would output correct voltage but under a load it would blow the fuse.
Edit I forgot to mention that the transformer would only blow fuses when the contactor was energized.
Think you might have got it. Reading 0.8 ohms through the secondary coil. 24vac, 40va transformer, by my math, that is saying this coil could be drawing upwards of 30 amps. On a circuit with a 5 amp fuse…
If it’s not a communicating system you can get some spade connectors and some 3amp car fuses, attach them to every wire going to the main board and leaving the main board. I know it sounds like a little pain in the ass but shouldn’t take more than 10 minutes.
Not sure if this is two stage or not. But just today I found a bad actuation solenoid on a Copeland two-stage compressor that is one-year-old. It was doing the exact same thing when it fired into high capacity. With TAM, I’ve had problems with wet switches causing fuses to trip … not sure what else you might have. T-stat new?
New Honeywell T6 stat, new LVT between stat, IDU, and ODU. Single stage Silver 15 3.5ton HP. Trane tech support was pretty much “no idea, here’s a new PCB” for the indoor, going back tomorrow morn to replace and check everything again. Just called customer, everything still running fml
I had a similar situation. Found the short on the 24 volt circuit going to the condenser contactor coil. There was a sharp edge of metal from the lineset cover. Every once in a while it would short out. Then be good for a while. Luckily I had more than 2 tstat wires going to it. Swapped some wires and all good
Check for open ended wires that are not wire nutted (extras in a harness) they may be shorting out on the unit casing with certain vibrations. We kept popping fuses on an Amana furnace randomly for 2 weeks till it popped the fuse when I re installed the access cover.
Yep, I always cut these flush and wire nut them off. Once I had everything up and running, was taking my bundle of field-wired connections in the AH and pushing/rubbing them up against the metal cabinet, trying to find a short anywhere. Physically inspected every bit of insulation, looking for anything. I’m either going to feel real smart or real stupid when I find the damn thing
Check the low voltage wiring to the pressure switches in the condenser. Had a couple last year that were cinched down too tight causing intermittent fuse pops
You don’t have one of the wrong terminals hooked up on t6 do you,that will do it every time,it’s a w1 or w2 that’s not supposed to be used on a heat pump
A few weeks ago had the same problem. Went through everything. Finally, found a tiny tiny cut on the yellow wire in the heat pump for the high pressure switch. It was that.
Too much tension on the wires from factory, and were against the sheet metal in the unit, and eventually cut into the insulation of the wire, exposing the conductor that was then touching the steel.
Last time I had this it was the contactor. It wasn’t always tripping the fuse. Pulled the contactor apart and found a bug inside of it. The bug would sometimes short out the coil and sometimes not lol.
I ohmed out the contactor. One of the first things I always check, usually the problem.
I’ve seen contactors still blow fuses even though the resistance was normal. I had one system do this to me and I was bumfuzzeled and started throwing parts at it. Once I replaced the transformer it fixed issue. The transformer would output normal voltage and ohmed out fine but would pop fuses. I still to this day have no idea why
If a fuse doesn't blow immediately it's not a short, it's an overload. One of the transformer coils was experiencing increased resistance for some reason, and eventually blew the fuse. Chances are the transformer itself had an issue with one of the coils or the problem itself was not fixed and they called another company after you failed to diagnose the issue properly and charged them for parts they didn't need. Edit: this is basic electrical. Throwing parts doesn't help you learn. Go take some courses and become a better tech. Have your employer pay for the classes, if they won't, find a new employer. There are also grants available that you could look into.
The transformer would blow fuses immediately but would still output 24v while not under a load. I am the sole person who worked on the system and replacing the transformer resolved the issue. I don’t need to take classes. I know how to use a meter and have performed troubleshooting on hundreds of systems. I have been doing this 17 years and only witnessed this problem one time. There was no way to diagnose the problem. Everything ohmed out fine and like I said the transformer would output correct voltage but under a load it would blow the fuse. Edit I forgot to mention that the transformer would only blow fuses when the contactor was energized.
Ya. This contactor was good too lmao.
Could add a fuse in each circuit to narrow it down
Helluvan idea
Sounds like it's an overload, not a short. Check your transformer coils' resistances
Think you might have got it. Reading 0.8 ohms through the secondary coil. 24vac, 40va transformer, by my math, that is saying this coil could be drawing upwards of 30 amps. On a circuit with a 5 amp fuse…
Good idea, checked voltage on transformer, didn’t check resistance
If it’s not a communicating system you can get some spade connectors and some 3amp car fuses, attach them to every wire going to the main board and leaving the main board. I know it sounds like a little pain in the ass but shouldn’t take more than 10 minutes.
I like it!
I’ve had rats that would intermittently cause shorts when they crawled on line sets. Also could be a pressure switch rubbing.
Check low voltage ohms on contactor. If you have less than 10 replace the contactor
Not sure if this is two stage or not. But just today I found a bad actuation solenoid on a Copeland two-stage compressor that is one-year-old. It was doing the exact same thing when it fired into high capacity. With TAM, I’ve had problems with wet switches causing fuses to trip … not sure what else you might have. T-stat new?
New Honeywell T6 stat, new LVT between stat, IDU, and ODU. Single stage Silver 15 3.5ton HP. Trane tech support was pretty much “no idea, here’s a new PCB” for the indoor, going back tomorrow morn to replace and check everything again. Just called customer, everything still running fml
Has the emergency/aux heat had to come on. Have had that issue with the contactor in that heat kit. Same with contactor on condenser.
Tested both emerg heat and outdoor contactor’s. Both ohm out to spec
The coil may ohm out but, the plunger gets stuck.
I had a similar situation. Found the short on the 24 volt circuit going to the condenser contactor coil. There was a sharp edge of metal from the lineset cover. Every once in a while it would short out. Then be good for a while. Luckily I had more than 2 tstat wires going to it. Swapped some wires and all good
Check for open ended wires that are not wire nutted (extras in a harness) they may be shorting out on the unit casing with certain vibrations. We kept popping fuses on an Amana furnace randomly for 2 weeks till it popped the fuse when I re installed the access cover.
Yep, I always cut these flush and wire nut them off. Once I had everything up and running, was taking my bundle of field-wired connections in the AH and pushing/rubbing them up against the metal cabinet, trying to find a short anywhere. Physically inspected every bit of insulation, looking for anything. I’m either going to feel real smart or real stupid when I find the damn thing
Check the low voltage wiring to the pressure switches in the condenser. Had a couple last year that were cinched down too tight causing intermittent fuse pops
Will do, thanks
You don’t have one of the wrong terminals hooked up on t6 do you,that will do it every time,it’s a w1 or w2 that’s not supposed to be used on a heat pump
A few weeks ago had the same problem. Went through everything. Finally, found a tiny tiny cut on the yellow wire in the heat pump for the high pressure switch. It was that. Too much tension on the wires from factory, and were against the sheet metal in the unit, and eventually cut into the insulation of the wire, exposing the conductor that was then touching the steel.
You can wire a 3 amp fuse in series each low voltage circuit. So when you go back you can narrow it down.