Unfortunately, yes. Why did they install a 2 stage condenser when they knew you only had a single stage furnace?

there may be a work around by an experienced tech. However, I would not do that. You have two choices. Get a 2 stage furnace or send the two stage AC condenser back for a single stage. I don't understand how a dealer would sell you a package like this.

IMO

Can you post the model numbers of the AC condenser, furnace, and thermostat? Sometimes a single stage furnace may be able to accommodate two stages of cooling. You also need additional wire going to the thermostat, and a thermostat which can control two stages.

not disagreeing with above post but has nothing to do with the problem presented by OP.

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TD

Thank you all for responses. Yes, I have same questions as to why as this wasn't communicated before install. Good times.

Sorry for the ignorance here as I have about zero practical knowledge of these systems, but does the 2 stage condenser just send more refrigerant to the same coils during stage 2 operation? If so, does that just produce "colder air" from the coils? If yes, then how would the furnace's lack of more than 1 blower speed negate the condenser from being able to send more refrigerate to the coils? You'd just have the system sending the same volume of air at the same speed to the registers, it's just colder coming out. If my logic is sound, that's the piece I'm missing...

To Mike_Home's question:

Furnace – Carrier #59SC5A100S2120

AC - Carrier #24ACB760A320

Stat – Nest 3rd Gen

The Nest Pro Setup does show a 2 stage cooling / 1 stage heating wiring configuration in their documentation. That's what started this whole thing - I pulled the puck off after everyone left and found nothing in Y2.

Thanks all for the help!

Here is the 59SC5A installaion manual. Unfortunately this is a Carrier Comfort series furnace which only supports a single stage AC condenser. There are Carrier furnaces which are single stage heating, and two stage cooling, but this is not one of them. The condenser does have two stages, and the Nest can control multiple stages for heating and cooling. You need to discuss with the installer why he sold you this configuration. It doesn't make sense.

To answer your question, the high stage makes the coil colder, so the blower has to be set to a higher speed. If you don't then the coil will freeze and form a block of ice. The thermostat tells the furnace to change blower speeds and condenser stage settings. This is done with the Y1 and Y2 connections. Your furnace has a single Y connector.

@Mike_Home

Thanks so much for the explanation. Although it's bad news for me, you've solved my mystery. Really appreciate you taking the time help. As for the installer, we did have a lot of back and forth about upgrading to a 2 stage furnace/adding zoning, etc. The AC was sold as something that would be quieter and less expensive to run (as we aren't in a always hot climate) than the comparable single stage model. At no point though was I told that I wouldn't be able to use both stages unless I upgraded the furnace... that's some BS.

I would think your AC has been wired to run in the high stage only. I don't see how it will be quieter and less expensive to operate than a 5 ton single stage condenser. The condenser has to operate in the low stage to get those benefits. Otherwise it is constantly running as a 5 ton AC.

I hate to say this, but you paid extra for something you can't use with your current furnace.

You could use the 2 stage AC with the single speed furnace.

While that setup is not right (2 stage AC with single stage furnace) it can be done. (With the proper knowledge there is little you cannot do.)

But the HVAC industry is built around charging thousands of dollars for equipment and then conning you to hire the most illiterate people on the planet to install it, so you can save $$$ that winds up costing you more $$$ when it's not done right (cost of ownership -- you own it so now what?) Ask me how I know this.

The kicker in all of this: You have to call someone who actually knows what they are doing. (no gimmicks, no freebies... paid for service.)

Control problems, require control knowledge. No way around that.

I service the Katy, Texas area.

Austin, been a few years…

but yes 2 stage condenser with a single stage furnace

Get a 2 stage cool thermostat

Wire Y1/Y1 condenser to G from thermostat to control board

Wire Y2 to Y control board

Use high speed wire for cool on control board

Use the medium speed wire on fan on control board

So Y1 from thermostat to g will turn ac on at medium blower speed and Y2 will ramp the blower up to high speed

Kris Flowers, but can a 2 stage condenser work with a single stage furnace with a single stage control board (I have a Trane XE 90 furnace with an Emerson White-Rogers 50M56 CNT07541/CNT07648/CNT07679 Integrated Single Stage Hot Surface Ignition Control board)? I don't see any low/medium/high wires, just Heat Speed and Cool Speed. Are Heat Speed and Cool Speed different?

"Can a 2 stage condenser work with a single stage furnace (with a single stage control board?)"

Answer is still no. You can rig pretty much anything to do anything with the right equipment, relays and controllers, but it would be cheaper (and safer) just to buy a new furnace!

Nothing has changed... in business to do it for you, not argue a myriad of ways in which to do it.

Control problems, require control knowledge. No way around that.

I service the Katy, Texas area.