The outdoor design temperatures for Philadelphia are 89 degrees for summer and 15 for winter. He has over sized the furnace in my opinion. The summer design temperature is a little high, and he has the indoor at 74. The humidity values don't make sense, but I am not sure how much they affect the calculation.

Let's see what the tech has to say.

Tech visit two hours ago.

He said the AC was a little low on the charge so he added 8oz of R410a. He also checked pressures, they're 290/120 (12 degrees, something ... can't read his writing). He also checked gas pressures, which are 1.04 and 3.41. He also leveled the outdoor AC unit to reduce vibrations. He also found a large hole (1/2 dollar sized) behind the thermometer that he said may cause the temp to be read wrong so he filled it.

That's it. The unit is still short-cycling as of now. It's 81 outside and average humidity. My unit is set to 74. It's come on low-stage on/off every 7.5 minutes or so.

The tech could not articulate why the short-cycling is occurring. He said if it's maintaining the temperature then it's doing its job. He said the thermostat is set to detect a .5 degree increase so that could be flipping it on/off so frequently.

When I cut to the chase and asked him if he's saying the manufacture designed the system to short cycle, he wouldn't answer the question.

Aside from summarize something like this to the company I purchase it from, I'm not sure what else to do. Perhaps it's time to escalate to Carrier? According to Carrier, the company should do this on my behalf with their local rep?

If he thought the 0.5 degree was too sensitive, then he should have checked the anticpator setting in the thermostat.

I suggest you call the contractor and tell them you are not happy. If they ignore you, then call Carrier.

Fired a shot across their bow, hoping they admit to the issue and resolve it swiftly. In the meantime, if someone comes across a similar issue and doubts themselves, there is a good (albeit brief) article on short-cycling by Energy Star (here). Unfortunately, the Carrier manuals don't reference short-cycling to much

Vendor is dogging me. Escalated to carrier rep. Unbelievable. Wish there was a way to get some of my money back for the hassle.

Had a heated conversation with their manager in charge of installs. He insists it's not short-cycling and the unit is operating appropriately. He's going to have Carrier come out, but seems to think the Carrier rep won't feel there is an issue, too.

Is there a chance these Carrier guys would let something like this fly?

Anything is possible, but I don't see how the Carrier rep can say this it is operating appropriately. We are about to have several days of 90+ degree temperatures. Have him come soon.

I don't understand why the manager is getting short with you. He sends a tech for one visit who basically does nothing. He must be very busy and tired. Not very nice for a customer who has spent a lot of money on a top of the line system.

Carrier will be out on Monday. I read the ACCA manual and it says there is no situations where an installer should use temperatures outside their design tables. In fact, according to the Rhvac program they use (based on ACCA) they would have had to purposely change the design temps imported based on the location they selected for the calc.

Through a detailed review, I also found they used design grains of 30, when it should be 40. I also noticed they put the square footage of my house about ~200 sqft over what it really is.

I have no idea if these values and the two improper design temperatures mentioned above would result in a sizing difference of more than a 1/2-ton, but it will be interesting to see what they say.

I plan on keeping this in my back pocket and see what Carrier says first. Then ask Carrier to walk me through the load calc and see what they say about the data inputs. If they agree with the inputs, then I'll be confident the Carrier guy is protecting the installer, not me the consumer.

Get others to assist you & do your own FREE load-calc & SIZING.

http://www.loadcalc.net/

Let us know the cooling & heating sizes you get.

udarrell,

I've tried this, but what's not clear is whether "outside walls" and "windows" sqft is actually measurements of the wall or the room on that side of the house. For example, the entire back of my home faces North. How would I measure the sqft of the entire wall? Say my home is 150' wide and I have 9' ceilings and my home is two stories so I'd input 2,700sqft?

Hi,

Carrier came out today. They took a bunch of photos and grabbed a bunch of data from the tstat and will let me know.

The installer also came out and, upon my request, re-performed the load calculation using ACCA design temps. He said the company uses 95/0 for Philadelphia as their standard.

The updated load calculation, all else equal, suggested a requirement of 2.87 tons and suggested of 3.17. The installer said it's routine for them to round to the nearest half-ton and since two-stages don't come in half-ton sizes he still recommends a 4-ton.

Carrier also observed the HVAC run to maintain the set temp and it ran for 15 minutes. This is not what I've experienced ... I think given all the testing they were doing and all of us in the room talking by the tstat tricked it.

Going to re-test it this afternoon. The installer seemed to think they would be willing to refund me the difference in a one-stage/two-stage (since I really don't need the two-stage) or replace the 4-ton with a 3-ton.

Should I ask for a 3-ton two-stage?

It seems like every time he recalculates he gets a different number. I think the the design temperature for Philadelphia is 92-93 degrees. Is he still using 74 degrees at the for the indoor temperature? If he changed the indoor and outdoor by 1-2 degrees it would probably come out to around a suggested 2.9 tons. Then what does he do, not add the extra ton?

What was the calculation for the heating load? Is he still saying you need a 100K BTU furnace?

We can discuss the calculation all day, but the fact is what you have now is short cycling. My recommendation would be to get the 2-stage 3-ton condenser. When working properly it is very good at humidity control.

Hi Mike,

He re-performed the load calculation in front of me and I provided the ACCA numbers directly from their manual J (8th edition). Philadelphia is 89 / 15. Everything else remained unchanged, which I also verified.

I used the new Manual J info to perform a Manual S and came up with a minimum of 37061 btu's and a maximum of 44473 btu's. If I assume 12,000 btu's per ton I get a condenser range of 3.08 to 3.70 tons.

Required heating came to 72,824 down from 88,823, based on the design temp changes.

I plan to monitor the system for an hour to re-assure myself the short-cycling numbers are accurate. The fact Carrier saw it run for 15 minutes has me questioning how closely I watched the system. If it is indeed short-cycling like it has been, I will wait for Carrier to give their input and then proceed with the 3-ton two-stage.

I think I'll also make a stink about the oversized furnance unit and use it as a bargaining chip as it's a modulating unit I don't think it will have a negative impact on my home or the unit by being oversized (not taking into account the check book damage it did).

If it were my home, I'd get the 3-ton either single stage or 2-stage with a 3-Ton AL evaporator & a TXV metering device...

Had a third-party perform a manual S on the 3-ton version of my 4-ton equipment - it was more than sufficient for the cooling I need. Initiated the process with the installer to replace the equipment with equipment which is properly sized.

I do wonder about the furnance. Should I ask them to replace the modulating unit with a smaller one or will it not matter since it's modulating? Maybe just ask them the difference in $ between the same 80k unit?

If the duct work can handle the 100K BTU furnace then I would not bother replacing it. The extra capacity will come in handy if you do set backs in the winter. You hope the furnace modulates intelligently and will rarely go to the highest stage.

There is usually not much of a price difference between a 80K and 100K furnace. You will have to decide whether it's worth the fight.

Thanks, Mike. My hope is to use it to pressure them to replace the HVAC unit and I'll concede on the furnace.

The company did an energy audit on my house so I've got a plethora of data about my system. How would I determine if the duct work can handle it?

Any idea on the price difference between the Carrier 24ACB748 (4-ton) and Carrier 24ACB736 (3-ton)? I assume the air handler won't need to be changed, same line set, etc. They didn't write it down as 3-ton was never discussed so I suspect it will be a touchy issue.

If you have the Infinity thermostat then you should be able to see the static pressure reading when the furnace is at the highest stage. It will also tell you the air flow in CFMs. The static pressure should ideally be at 0.5, but something in the 0.6-0.7 is acceptable. A higher reading will indicate you have supply and return size problems. The filter should be clean when you do this, otherwise it will skew the results.

What size filter do you have (width, length, and depth)? A 100K BTU furnace needs a big return. That is the first place to measure.

I don't know prices of Carrier equipment, and it is difficult to find out without calling a distributor. My guess is the equipment price difference is in the $500-$700 range. The installed price is about double the number.

The problem for the dealer is not the price difference. It is the cost labor and materials to swap units. He is also has the problem of figuring out what he is going to do with the first condenser. I don't think he can sell it as new to someone else. He may try to resell it again but at a big discount. He is not going to be happy about the situation. All this grief because his salesman could not spend the time to do an accurate load calculation.

Thanks, Mike. I do have the Infinity, would I be able to see static pressure when the air is on or only when the heat is on?

For filter, I use a Nordic Pure MERV 12 20x25x5.

I thought it would be more of a cost difference, but maybe I'm thinking of the furnace differences the sales guy and I discussed (e.g., two-stage vs modulating).

Had the installer recognized the issue initially they would not have spent ~8 hours at my home the last 3 months trying to convince me it's fine and use that time to do the install again :-)

You can measure static pressure whenever air is flowing. It doesn't matter if you are heating or cooling. A MERV 12 filter is fairly restrictive. Do you need that much filtering? A 20X25 is small for a 100K furnace, a 25X25 would have been better.

I saw your load calculation. It said you have R19 insulation in the attic. Is that correct. For the walls it had R11, you may have R13, but that is not much a difference.

My wife has allergies so we went with MERV 12. Could go down to 10 or so if it would make a difference. Should I insist they change it to 25x25? I imagine they'd have to replace all the metal they added (photos above in previous posts).

My energy audit says I have R-18 - R-23 in the attic. They recommended at least moving to R-38 and sealing any other penetrations. No idea what's in the wall - it's rolled insulation and the home is a Toll Brothers build in 1991 or so.

The 20X25 filter is fine for the 3 ton condenser. It is not worth having a fight about changing for the furnace given that the furnace is rarely going to hit the high stage.

The static pressure should be checked. Your furnace will ramp up the blower to do whatever it takes to push the required air flow. It may have to work harder if the static pressure is high. Your duct work looks like it is adequate so it should not be a problem.

I have a reminder to replace my filter today (we usually do it every 6 months) so I will try to check the static pressure today/tomorrow.

Owner called me. Offered to swap out the 4-ton for a 3-ton. He stood by the design as RHVAC application recommended 3.17 tons and said the two-stage is for those extreme conditions and I'll wish I had it on 100 degree days. He's very concerned it will be undersized if they do the swap and said if he does the swap he wants me to sign-off that they're off the hook if it's too small.

I told him to let me think about it. I asked to have a commission report run before I make my decision, but he's never heard of it before.

Did anyone explain why it was short cycling on the low stage?

Installer offered to swap out the 4-ton for the same unit, but in a 3-ton at no cost. However, they're asking me to sign away their liability, which I won't do. I've provided them with updated load calc numbers and Manual S and asked them to dispute it and if they see no errors then I won't sign anything. We'll see. Still waiting on a final report update from Carrier, but based on some furnance errors I observed and, he still said the unit was operating normally, I think he was trying to protect the installer.

Essentially, the contractor has told me they will NOT provide a Manual S. That they've already tried to help me enough and they're spending too much time on this issue. They stand by their equipment and I either (a) sign a liability waiver for the smaller 3-ton and I have to eat the difference between the larger / small unit, or (b) be happy with what I have.

I contacted Carrier, who won't get involved.

I contacted ACCA, who hasn't returned my e-mail.

Nothing the State of PA or my county can do to help.

So I'm stuck with my dick in my hand.

I know you don't want to sign the liability waiver, but have you read it? Maybe it is your way out if you could change to terms to something acceptable.

I am getting a copy this week to look it over. If it's not written by a lawyer I'm sure it's not legally binding should something significant occur.

So I got intouch with my Township's code enforcement, which requires an ACCA Manual J and Manual S as part of the installation permit. The Township is now involved and getting the Manual S from the installer. :-)

Township is useless, but I did get the liability waiver, which reads "We will pump down and remove your existing 4 ton 2-stage unit and replace it, at your request and against our advice, with a 3 ton two-stage of the same model. We do not guarantee any level of comfort or savings as we feel that the 3 ton unit will be undersized during the days when you need it the most. The new unit will have the balance of the warranty of the existing unit and there will be no charge."

He's standing his ground and will not provide a Manual S. He and I agreed I either need to make a decision next week and sign the form (or be comfortable with the existing equipment) or take him to court. He's been cordial through the entire ordeal.

Although I have feedback from you, Mike, and another independent online contact, that my unit is oversized ... I can't get any contractor in my area to come to my home and run a Manual J and Manual S. All I have to go by is the installers Manual J. I know it's a math equation, but I am concerned about attesting to the form not being an expert in the HVAC area, whereas the installer has 25 years on me and a well respected and successful business in my area (even other contractors comment how they are the best in the business around here).

My concern is there are other variables at play that I'm unaware of and I'm worried the 3-ton 2-stage will not provide sufficient cooling on days when it's hot/humid and 90+ degrees.

Logically speaking, my current unit runs at stage one (2.7 tons) for 8-12 minutes on 90 degree days. The smaller unit would run at stage two (3 tons) for 30+ minutes, which is what's expected for a properly sized unit. There are times my existing unit runs in stage two, for example, when I decrease the set point from 74 to 72 on a 95 degree day ... with the new unit it will just take a little longer to get to the new set point.

If you were me, would you sign it and get the smaller unit?

What humidity levels have you seen during the summer? If you are in the mid 40s, then I would be inclined to leave the 4 ton unit. If you are seeing in the mid 50s, then you are not getting good humidity control.

Did you ever get a copy of HVAC calc and do your own load calculation? I have never used it, but I have read good reviews. It would be worth the $49 investment.

Haven't made a decision on the swap, but I'm now hyper-focused on my HVAC. Now that we're seeing temps between 30-40 degrees my furnace is turning on. It's a modulating unit, but is running at 100% for the entire cycle. It does this here and there throughout the day (independent of set temp changes), but otherwise modulates.

Any idea why the modulating unit would opt not to modulate several times a day?

It could be an installation problem. The furnace control board may not be set up properly to allow the thermostat to stage the furnace. It should not be at operating at 100% with the temperatures with the mild weather we recently had.

Well the owner is apparently sick of me (or all the issues I found from his poor install) and has offered to pull out all the equipment and give me my money back. Can't believe it!

The owner came to his senses and we're now replacing the 4-ton 2-stage with the same version, but in 3-ton 2-stage. Finally it's over :-)

Awesome

Did you need to sign the liability waiver? Was the issue of the furnace running 100% at all times resolved?

I have not signed it, but it could be gleamed from my e-mail to the owner so I suspect it's the same (or they will have me sign it when they come to do the install). The 100% furnace run was resolved ... there was some type of cap that was supposed to be removed during install but wasn't. This means the furnace wasted a lot of gas last winter! Happy it's resolved, but disappointed it took 5-6 techs to figure out what appeared to be an obvious 1 minute fix.

That is what I suspected. I believe the Carrier furnaces are set up at the factory to stage from the control board and the not the thermostat. The furnace settings have to be changed. They are usually some DIP switches that need to be flipped, but your furnace may be different.

Good luck with the new installation.

wow. what a nightmare. i feel ours is just beginning. glad you got it all worked out. i've figured out that one has to be an hvac specialist before one can purchase an ac for his/her house or you can really get screwed over.

Seems like there is a problem with the amperage being too high on the system may be your unit needs a different capacitor.

www.chicagohvacservice.com

Seems like the running times are normal. You might want to install a hard start kit to take away some of that starting amperage to prevent that flickering this help sometimes and in regards to the vibration install some nice vibration pads under the equipment and that should take away that problem the compressor might be tightened too tight to the housing of the unit outside as well taking away the vibration pads under the compressor these little things to help out a lot good luck to you.

www.heating-repair-chicago.com

Do you know if installing a hard start kit would violate the Carrier parts warranty?

Violate MFG Warranty: only if it was the wrong kind or installed improperly causing damage to the compressor.

With that said, most modern HVAC compressors do not need hard starts these days. Usually, if one is required to start a compressor it typically indicates failure of the compressor. While you can 'sometimes' install a hard start kit to save a compressor sometimes this only lasts a short while.

Typically what this means is that the bearings with in the compressor are failing. (seizing up) and so the compressor doesn't have enough power to start on it's own. By adding a 'proper' hard start kit (there are many configurations, because there are different types of compressors / different sizes in tonnage --if you use the wrong kind for the wrong compressor it can damage the compressor in addition to the damage that required you to install the hard start to begin with.)

The best is a 3 wire hard start kit in which your HVAC contractor chooses the proper start capacitor as well as the starting relay. As mentioned earlier there is a bunch of different kinds. A knowledgeable HVAC contractor will know which kind you need. Others will just put in a packaged 'kit' that probably won't work for very long in some cases.