re: Identifying single stage, multi stage and variable speed AC units

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So basically any single stage with an EMC blower can be described as variable speed? I can tell you that he’s the only one that described a single stage unit as variable speed and even Carrier said it’s definitely not a variable speed. Not trying to be too defensive but I’m 100% sure that’s the argument he’s going to use

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Just wanted to make sure we are talking about the same thing. The compressor in the outdoor unit is single stage for a Performance Series Condensing unit. It is On/Off. We are not talking about that. The variable speed that they will be trying to explain is for the indoor section.

For the indoor supply fan (part of the furnace assembly) the motor is probably an ECM motor, although some manufacturers still use an X13 motor. Point is this is where they will say it is variable speed. In my house I have a two speed compressor and a modulating furnace. My unit stages the indoor supply fan for "Cooling Low" or "Cooling High" or "Heating Low"or "Heating High" based on my indoor space temperature and space set point. So it varies the speed of the supply fan depending on the state of compressor or furnace commands. That is what makes it "variable".

Here is a simple explanation for X13/ECM/PSC motor use in residential ac.

Variable Speed

You need to understand the difference between variable speed and variable capacity.

Variable speed refers to a blower motor in the indoor unit. With a single stage outdoor unit, it will still only run at one speed but will ramp up slowly at the start.

Outside units will be called variable capacity and those will be much higher than 16 seer.

Odds are your indoor unit is variable speed to get the 16 seer rating. Be careful not to be an arse if you actually got what you were supposed to.

For the record, a single speed system properly sized will be very efficient, quiet and be a much better value than a variable capacity system.

Much appreciated, that is why I don’t want to put him on blast because there’s definitely a chance my expectations were just different than what he was planning. From what I can tell online that furnace is not expensive and should’ve been included in the other two companies that quoted me much less for a 16 seer single speed. Doesn’t seem to be an upgrade and none of the others described it as a variable speed unit.

He had said “$15,990 for the 5 ton and duct work.” I then asked, “Is that for a 16 seer carrier single speed or higher seer?” He responded,”16 seer variable speed Performance Line”. And then I asked him, “Assume that's better than the 16 seer single speed” and he said yes.

I have a 2 stage 4 ton A/C that's 14 seer. There are 2 compressors in the outside condenser unit. One is 1.5 tons and the other 2.5 tons. There is an outside thermostat set at 85 F. Below that the smaller compressor comes on first. Above that the larger compressor comes on first. If the inside temperature goes 1.5 F above the set point (usually 73/74 F), the second compressor comes on. Seldom do both compressors run at the same time. The inside thermostat indicates if 1 or 2 stages are running.

The air handler in the attic is variable speed and ramps up and down as needed.

It's made by Nordyne. Works great. Saves me on energy bills.

Heating uses electric heating coils (also 2 stages).

Update? I've been lurking.

I should’ve updated on Monday. He was very defensive when we first met up because I had told him a couple times that he did not install what he quoted me going into the meeting, and obviously people don’t like being called a liar. He started going on and on about how the variable speed part that he was talking about was the furnace as others predicted. I let him go on for a couple minutes to allow him to hang himself, knowing all the while that he had installed a base model single speed comfort series rather than a variable speed performance series (even though nobody, including Carrier, describes that as being a variable AC system).

I then presented him with the spec sheet that showed all the different furnaces on it with the picture of my model number off the furnace and he immediately said, “shite you’re right. My supply guy sent the wrong one and I wasn’t here to double check it. I never intended to install the wrong one and I will get that swapped out immediately.”

True to his word they came today and swapped the inside unit out with the more expensive Performance series. Their work looks really good and the unit is pulling a much smaller load than my previous unit. At the end of the day I’m happy with what I got and I do believe he genuinely had no idea that he installed the incorrect indoor furnace, although my wife and friends think he was lying and just realized he was busted. Either way I put the brakes on swapping out my 3.5 and 2.5 tons since they are working but really old(20+ years).

We did have a lengthy discussion about how when he says he’s installing a variable speed AC none of his competitors, or Carrier, are describing it that way because the compressor is just a single stage. He said he understood but said he was busy when he quoted me and should’ve taken extra time.

Sorry this is so lengthy. Glad the saga is behind me and now I’ve learned more about AC systems than I ever imagined

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Right. Not swapping that for a nest. It can't change the speeds of the motor. Just off and on.

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I may have the terminology wrong, but my nests work great with my 2 stage unit. I went through a period like the OP where I doubted my install guy. Turns out, he wasn't lying about what he sold me-his tech did not run the proper wire for stage two to activate on one of the two that were installed. These units have been absolutely wonderful. Cooler house and lower bills. Stage one is super quiet. Stage two isn't, but it doesn't always come on, and when it does, it doesn't stay on long.

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Most people wouldn’t recommend Nest. The documentation and support is pretty bad compared to others.

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I read this all the time. Mine have been fantastic.

My nest was awesome also. Until I moved into a house with a carrier infinity. You can rig it up to work on the variable speed unit but it's going to only turn it off or on and not change the speeds.