I should have done this in the Winter.

SO for whatever reason, our wire that runs from the outside AC condenser through the brick up into the attic and to the Main System doesn't get sufficient power. It degrades or something. When it gets really hot outside I am randomly having to reset the whole system to get the unit to run. Two different AC companies have been baffled by this. The house was struck by lightning a few years ago so they think that may be it. I got quotes to replace the wire, $275+, depending on how hard it is to get the wire through the wall.

The last guy said he would just run the wire up the brick and right into the attic. That sounds a lot easier for me as the existing wire is grouted in or something...doesnt budge. I'm gonna try it myself.

My question is...what type/gauge of wire do I buy for this and where do I get it? Big box?

Thanks for any help.

You are talking about the signal/thermostat wire?

Does the signal/thermostat wire run all the way to the outside condenser?

He's referring to the Y and C wires that go between the furnace and condenser.

I assumed the thermostat wire ran from the thermostat to the main unit and this wire I'm needing to replace runs from the condenser to the main unit. 2 different wires??? I hope...

Lobster Twins said:

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I assumed the thermostat wire ran from the thermostat to the main unit and this wire I'm needing to replace runs from the condenser to the main unit. 2 different wires??? I hope...

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Yes. It is control wire so it should be 18 AWG.

https://www.homedepot.com/p/Southwire-500-ft-18-2-Brown-Solid-CU-CL2-Thermostat-Wire-64162144/202316306

Yes, it's a furnace! I always say the main unit. Thank you very much!

Sometimes you can buy it by the foot if the roll is too much/too little.

How did they diagnose it to be the wire? I can't see lightning damaging wire. Maybe the control board.

Or a critter chewed through the wire. I'm just wondering how they narrowed it down.

An easy way would be to disconnect it at both ends, twist the two wires together on one end, and test the resistance on the other end.

1999 HVAC problems again in 2014
Solution suggested was to abandon old 4-wire cable via
18/8 cable from attic evaporator to outdoor compressor 5-wire bought from Lowes
Started at condenser, through attic to a soffit, then stapled to soffit until dropping near compressor
Solved

Even new 2021 system replacement used this wire, I think

Maybe chewed inside a wall? The wire has been cut and redone...which they checked as well.

I can't remember what they used but they tested the wire outside at the condenser and it was degraded for some reason. They basically said it's not getting enough power. It's over my head.

They didn't seem to know why either. I figure at the minimum I am out less than $50 to check a different wire. I don't really have the tools to test the resistance. What would I need for that?

tgivaughn said:

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1999 HVAC problems again in 2014
Solution suggested was to abandon old 4-wire cable via
18/8 cable from attic evaporator to outdoor compressor 5-wire bought from Lowes
Started at condenser, through attic to a soffit, then stapled to soffit until dropping near compressor
Solved

Even new 2021 system replacement used this wire, I think

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tgivaughn,

Maybe I'm misreading. Are you saying go with 18/8 from the condenser to the furnace?

18 ga. Wire

Get it with at least as many wires as you need.

If you want redundancy, get it with more wires in case one or more fail. Then you can just switch wires.

This is a heat pump system solution I offered in case it was similar enough to help.
Wire mentioned goes from attic unit to outdoor unit.

You will not be able to pull the wire. As they run the low side copper and wrap it with insulation as they tape it they are also taping the thermostat wire with it And that is why it will never be able to be pulled

maddiedou said:

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You will not be able to pull the wire. As they run the low side copper and wrap it with insulation as they tape it they are also taping the thermostat wire with it And that is why it will never be able to be pulled

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Yes, I have pretty good access to the wire from the soffit area to the furnace and it is wrapped exactly as you say.

The issue is from the brick to the soffit area as they actually surrounded the wire with the brick mortar...as in it won't budge until you break that mortar. That's what I think I am going to try first. I would much rather snake it if I can than have a piece of plastic going up the side of my house.

I guess to put it how the AC company told me in the dumbed-down form...the output from the furnace is sufficient but the wire is not carrying that full output to the condenser.