New replacement A/C System help/advice ??

[socca]

To change speeds, the energized speed had to be turned off, then it waited 5 minutes for the head pressure to subside, then it engaged the other speed winding.

I have an 11-year-old 2-stage Lennox heat pump (3 ton, 18.6 SEER) in a 1700 sq ft Florida ranch. The high stage sometimes kicks in for a few minutes according to some trigger that I haven't yet figured out; the A/C mostly runs the low stage when it runs at all. The unit never starts up in high stage, and there is no gap when transitioning between low and high stage. I'm assuming here that noticeably higher blower speed corresponds to high stage operation.

I've been satisfied with the heat pump for the 4 years I've owned it, and I'll be strongly biased toward getting another heat pump similar to it when it comes time for replacement (goes out of warranty next year).

BTW: the previous owner paid $9.5k (after Lennox rebates) to have this unit delivered and installed by a local reputable HVAC contractor. The time of year was April, so it wasn't an emergency install.

 

[Texas Proud]

Before making a purchase, I recommend contacting your power company. Some power companies around the country offer rebates for buying energy-efficient appliances. We've gotten rebates over the years buying a new heat pump and a new refrigerator.

It's worth the phone call.

If the AC guy did not know about any rebates offered then do not hire him... the bids I got all knew about the rebates... I made zero phone calls...

 

[Texas Proud]

I see you did buy, but I was wondering why you would get a quote for a single stage with variable fan... I would think a single stage would only need a single speed fan... that variable is a waste of money...

 

[REWahoo]

I see you did buy, but I was wondering why you would get a quote for a single stage with variable fan... I would think a single stage would only need a single speed fan... that variable is a waste of money...

Having the fan start/stop gradually rather than full-blast on or off is a nice feature.

 

[ERD50]

I see you did buy, but I was wondering why you would get a quote for a single stage with variable fan... I would think a single stage would only need a single speed fan... that variable is a waste of money...

Having the fan start/stop gradually rather than full-blast on or off is a nice feature.

+1. The other advantage is that the variable speed fan can help with taking humidity out. If the A/C doesn't need to run full blast, the fan runs a little slower, which gives the air a chance to cool further and more water vapor condenses out.

Our two level compressor does that, and it really makes a difference. It would work with a single level compressor too.

-ERD50

 

[triangle]

Our 19 yr old TRANE A/C is dead -

It was a single phase condenser with a single speed Air Handler, 5 Ton, 10 SEER, was put in by the builder for a 2300 sq ft single story house in Orlando.

Life was good before it died...., the Two of us were comfortable enough, ignorant about the newer, more complicated systems out there, which we never previously had to know the professed increase in comfort. The Electric Bill was around $150 a month & was not a concern.

Our Echo Bee Thermostat did show humidity of 70% & above many times with our older system, which although concerning we took it as a part of living in the hot & humid climate of Orlando.

The Estimates which are being quoted for the new system with a variable speed fan motor & 16 Seers are $2000 higher for a 2 phase & $3000 higher for a variable stage Compressor respectively compared to a new single stage Compressor.

Any help/advice regarding which system to choose will be greatly appreciated .
Anyone who has lately changed to the newer, technically higher A/C systems care to put in a few lines about their increased comfort or increased maintenance complications with their newer systems ??

Thanks & with best regards

I only skimmed other responses and see that you have already bought a new system, but it was not clear how dead your system was. An AC unit not starting is often caused by a blown startup capacitor. And higher humidity might be a symptom that your system needs a refrigerant top off. My home has a 30 year old Trane HVAC system that is still giving good service. A few years ago I considered upgrading but when looking at the numbers (cost of new unit, supposed efficiency gain, estimate of current electric consumption based on overall household consumption and how much it might improve) I did not do it. After adding refrigerant, the system cooled better (more quickly) than it had in years.

A second reason I did not upgrade was that the newer units have a reputation for not lasting very long before needing major service or replacement (less than 20 years). I don't quite understand what is going on there, whether it is true or just a small subset of people complaining loudly. But the new HVAC salesman and repair technicians seemed to have the same opinion.

 

[Telly]

I have an 11-year-old 2-stage Lennox heat pump (3 ton, 18.6 SEER) in a 1700 sq ft Florida ranch. The high stage sometimes kicks in for a few minutes according to some trigger that I haven't yet figured out; the A/C mostly runs the low stage when it runs at all. The unit never starts up in high stage, and there is no gap when transitioning between low and high stage. I'm assuming here that noticeably higher blower speed corresponds to high stage operation.

Thanks.
For sure yours would be a scroll compressor. The old reciprocating compressors had pistons in cylinders instead of the interlocking scrolls of a scroll compressor. The reciprocating compressors, when shut off, did not allow refrigerant under high pressure at the compressors output, to bleed back through the compressor to the low pressure suction side. The only way pressure could equalize in the system was for refrigerant to make its way through the TXV or capillary tubes at the evaporator, back to the low side, and this took time. If the compressor was restarted before this equalization, the the compressor started against a very heavy load, which stressed the electric motor driving it. A lot of electronic thermostats had a 5 minute or so timer in them, to prevent a restart within X minutes of shutdown.

IIRC, the Scroll Compressor only seals tight when the compressor is running, otherwise the moving scroll floats loosely in the fixed scroll, at least that's what I think I remember. So maybe the scrolls not sealing when off allows the head pressure to equalize very rapidly, right at the compressor, where the pressure differential would be the highest. That may have then allowed much simpler controls for a two speed compressor, and a rapid changeover of speeds.