# Not feeling two stage cooling in new installed system



## huangfeng212 (8 mo ago)

Hello, I got my new system installed(Lennox 16ACX, ML296V) last month, and Nest wired as 2-stage cooling. What concerns me is I double it the system is wired as 2-stage cooling. I never had 2 stages of cooling before, but it feels like the 1st stage is pretty strong cooling and I don't feed the comfort improvement with 2 stages at all.
I checked the installation manual on both the furnace and ac unit and found 2 suspecting points.

1. The furnace manual says:

"The unit is set up at the factor for single stage cooling. For two stage cooling operation, clip the jumper wire located between the Y to Y2 terminals on the integrated ignition/blower control board"

So what does this "clip" mean here, does it mean to cut the jumper wire that is there for the default single stage? I opened the furnace door and found a jumper wire between Y and Y2 is there, no cut. I doubt the crew forget to do that and left my used as a single stage AC?

2. Next question is about the wire from the furnace to the outdoor unit, my old system had 18-2 cables, so only 2 wires in that cable, and my 16ACX manual shows there should be 3 wire to the outdoor unit, Y1, Y2 and C. However that 18-2 wire goes outside now connects to the Y1 and Y2, and there is no wire for the C connection. Seems like they should change out that cable to a 3 wire cable and they somehow cut corners to have a C wire from elsewhere in the outdoor unit?

I am going to reach out to the company that installed my system but I'd like to get some education from elsewhere first to better understand this. 

Thanks in advance!


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## droopylee95 (Feb 26, 2018)

huangfeng212 said:


> Hello, I got my new system installed(Lennox 16ACX, ML296V) last month, and Nest wired as 2-stage cooling. What concerns me is I double it the system is wired as 2-stage cooling. I never had 2 stages of cooling before, but it feels like the 1st stage is pretty strong cooling and I don't feed the comfort improvement with 2 stages at all.
> I checked the installation manual on both the furnace and ac unit and found 2 suspecting points.
> 
> 1. The furnace manual says:
> ...


2 stage system are 2 stage for increased efficiency. It only pulls the second stage in when there's a demand for it. Usually higher temperatures outside. When both stages are on the compressor is running full capacity an pulls higher amperage. 

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## Steven123cool (Mar 2, 2021)

huangfeng212 said:


> Hello, I got my new system installed(Lennox 16ACX, ML296V) last month, and Nest wired as 2-stage cooling. What concerns me is I double it the system is wired as 2-stage cooling. I never had 2 stages of cooling before, but it feels like the 1st stage is pretty strong cooling and I don't feed the comfort improvement with 2 stages at all.
> I checked the installation manual on both the furnace and ac unit and found 2 suspecting points.
> 
> 1. The furnace manual says:
> ...


Yes cut the wire between y and y2. Also run a new 18-3 or better get 18-6 to your condenser location. Your next upgrade may be a heat pump and you will need all six for that. At the condenser connect y1,y2, and “C” common to the common. Walla. Right now you run on second stage all the time with the jumper and I don’t know how your condenser is running


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## channellxbob (Sep 27, 2020)

Steven123cool said:


> Yes cut the wire between y and y2. Also run a new 18-3 or better get 18-6 to your condenser location. Your next upgrade may be a heat pump and you will need all six for that. At the condenser connect y1,y2, and “C” common to the common. Walla. Right now you run on second stage all the time with the jumper and I don’t know how your condenser is running


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## channellxbob (Sep 27, 2020)

Good advice above, I too am wondering how it's running at all with no common. There has to be something else going on you're not catching. The contactor cannot pull in without a common connection. You are definitely running on stage 2 all the time.
But for sure cut the jumper and connect the y1 and y2 and common as directed above and all should be fine.


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## droopylee95 (Feb 26, 2018)

channellxbob said:


> Good advice above, I too am wondering how it's running at all with no common. There has to be something else going on you're not catching. The contactor cannot pull in without a common connection. You are definitely running on stage 2 all the time.
> But for sure cut the jumper and connect the y1 and y2 and common as directed above and all should be fine.


They could have the common side of the contactor going to ground. Not exactly the proper way to do it but it would work. Lot of airhandlers will ground the common side of the transformer. 

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## Steven123cool (Mar 2, 2021)

I don’t think that will work. Has to be the common from that 24 volt transformer only.


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