I just had a 4 ton 16i, and variable speed air handler installed, but unfortunately, the people who installed it are not inspiring me with confidence that it's set up properly. For example, they installed the air handler with the default switch settings, which don't allow the enhanced mode to work. They only changed this when I called them back because my variable speed airhandler wasn't doing anything but turning on full blast. They would have left it that way forever if I hadn't caught it, so I have to wonder what else they did wrong.
I've tried to confirm the way they wired it up, but it doesn't seem to conform to any of the options in the installation book. I could post the wiring at the air handler if needed, but I haven't checked the other end of the wiring at the thermostat, or outside unit.
My first, most basic question is about the 16i's two stage compressor. I was under the impression that it can run at two different speeds, or capacities, almost like a true dual compressor unit. Is the switching for this two stage feature done internally to the 16i, or does it have to be treated by the thermostat as a dual compressor unit? There's a setting on the XT500C thermostat that has the option of "one cooling cyle, and 2 heating cycles", or "two cooling cycles, and 3 heating cycles". Mine is set to the first choice, but I wonder if the two stage compresser means it should be set to the second.
The next question is whether the air handler fan should run slower when the 16i is in it's lower "stage" mode? At the moment, mine seems to do just what the book says for enhanced mode, where it ramps up to 50%, then 80%, then 100%. This moves a lot more air than our previous unit did, and can get pretty noisy. My hope was that this variable speed air handler was going to be very quiet most of the time, but that hasn't been the case so far.
Any answers to the staging question would be most appreciated.
First of all, Rusty, you don't want to be opening things up and messin with wires to begin with. You may end up voiding warranties with the manufacturer. The correct diagram to use for the low voltage wiring would be "one stage cool, two stage heat". Also the speed of the outdoor compressor will not effect the speed of the indoor variable speed motor. That ramps up according the the dipswitch settings your mentioned before. If you really think the installers didn't do a good job with setting the system up, call the owner of the company or the supervisor, if your not satisfied with either of them, call Trane.
Jason the Mushroom
That stat can handle the 2 stage outdoor unit but comes factory set for std outdoor unit only. If they weren't smart enough to set up the VS indoor unit, they probably couldn't figure out how to use the keypad to set up the stat correctly.
If wired right, the air handler should move less air on stage 1 and ramp up to normal speed when stage 2 of the compressor calls. Electric heat has its own CFM setting. Y1 which is 1st stage comp would go to Ylo on the air handler telling the AH that the comp isn't running at 100%. This is 2 stage wiring to match the 2 stage outdoor unit you have!
Thanks for the comments. I only opened the unit up to verify the settings, and wiring. If I find any (further) reason to believe it's not set up properly, I'll certainly have them change it rather than doing it myself and voiding the warranty. As far as I can tell, it isn't set up like any of the 3 examples in the installers guide, so I'm not sure where that leaves me.
Another question is about a noise that the air handler makes as the heat starts to come on. It sounds just like a hard drive thrashing away for about 20 seconds. I'll ask them about that when they come back out to fix some other issues with the installation, but I already know what they'll say.
I guess I'd like to know more about just what the two stage compressor does. Can anyone recommend a site that will explain this?
I'm sorry to hear that the air handler fan won't run slower during normal operations. I've got two co-workers who've had 19i units installed, and they both rave about how you can't hear the air handler, and how it almost never goes into high speed mode. I'm now starting to worry that this is perhaps something that only works that way on the true two compressor unit. If I had known that, I'd have bought the 19i.
BTW, the last time they were out, it was their best two techs (who really did seem to know how the unit worked), and their manager. If you've got a phone number for Trane, I'd like to have it. Hopefully, it won't come to that though. I'd like to think they have everything right now, but for the money I paid for this thing, I expect it to 100% correct. Unfortunately, there were a number of things they promised and didn't deliver (yet), so they lost my trust from the very beginning.
Thanks for your time.
This is exactly what I was hoping to hear. Is there any way for me to tell when stage one is one, versus stage two? Can I hear the diff in the outdoor unit?
Originally posted by BaldLoonie
If wired right, the air handler should move less air on stage 1 and ramp up to normal speed when stage 2 of the compressor calls.
The biggest question is how do I, as a homeowner, convince the local compay's best techs, and manager that they don't have it set up properly?
Thank you very much!
Your thermostat should be set up for 2 cool/3 heat. In the installer setup in the thermostat it needs to be told it is controlling 2 compressors for cooling and for heating. I know the system only has 1 compressor, but it does have 2 stages. If the thermostat is set for a 1 compressor system, it will never call Y2 for 2nd stage of the compressor for cooling or heating.
If your installer didn't know to set up the thermostat properly, I would question the control wiring too. Did they set the dip switches on the varriable speed controller for the correct indoor and outdoor unit sizes?
When everything is set up correctly, the airflow will be lower for first stage than it is for 2nd stage. Your first stage cooling/heating output will be higher than your friends XL19i system, but otherwise should operate in a similar fassion.
[Edited by mark beiser on 01-24-2005 at 08:00 PM]
If more government is the answer, then it's a really stupid question.
You need to get your installer back out there and pose the same questions to him. If the ductwork is capable of supporting 4 tons of airflow that system should be extremely quiet. Make sure they check it out completely in both speeds with gages on it.
Thanks for the additional excellent info.
Mark, I suspected that it needed to be 2 cool/3 heat, but I asked the last tech if anything in the thermostat needed to be programmed, and he said no. Sigh....
I'm also willing to bet a reasonable sum of money that the control wiring is wrong as well. The dip switches seem reasonable (now) to me. 1,5,6, and 8 are on.
From the additional searching that I've done here, it seems that stage one is 67% capacity, and the AH can't match that capacity exactly. It sounds like it takes the next higher setting of 80%. If I read all the posts correctly, stage one will run at 80%, and stage two at 100%. Not as much difference as I'd like, but better than nothing.
Golan37, our ducting was originally set up for a 3.5 ton unit, but I don't know what CFM the old AH ran. I'm sure it was far less than this one is running though. So far, I haven't seen any instruments to measure airflow.
Again, I really appreciate the info and advice. My plan for tomorrow is to call the closest Trane office (Mobile AL), and have a chat with them. There are also issues of promised rebates that don't seem to exist, so before it's all over with, I might end up calling the giant home improvement store that sold me this unit, and telling them to have their folks come get it. Hopefully, it won't come to that.
I was looking at the instruction page. Low speed airflow is supposed to be 80% and high airflow is 100% of rated capacity.
Did they do a new duct system or are you using the old duct system? Did they do a load calc for you. It just sounds like it is too big, too much air for the system. Found several V/S, 2-stg systems that were added onto smaller duct systems, thinking maybe boost the equipment size and not the ducts. For whatever reason. And you'll hear it, epsecially when the Aux. heat kicks on.
If they didn't bother to wire it right, I'd have to think they didn't do to well with the ductwork either.
BTW, was it a HD contractor?
A homeowner's point of view
I question what was the justification for going to a 4.0 ton air handler. From what I have heard it is far more likely the previous system was oversized rather than undersized. Had they downsized the system rather than upsizing it, perhaps there would be no duct problem.
It sounds as if they did not do any load calculation nor duct design. Possibly you might make this the central point of your discussion with the big-box store, and compel them to back up and reconsider their sizing decision. From all that I have heard, if they didn't do a Manual J load calculation or some calculation corresponding to that, then they just threw some crap at the wall to see if it would stick. Demand to see their load calculations.
I am a homeowner. Got a 4.0 ton American Standard variable speed air handler to "match" a 2-year-old 3.5 ton Trane AC, when there was previously a decrepit old 3-ton air handler. It was what the AC company recommended, I thought it was innocent and conservative enough at the time. However the default 1400 CFM airflow revealed what was an inadequate duct design. Some of the ducts got above 700 ft/min airspeed and became noisy until I scaled down the air flow to 350 CFM/ton, around 1225 CFM. So I am speaking from experience of how to do some things wrong. My longer term hope is to justify a downsizing of AC, and then perhaps there will be no problem with the capacity of existing ductwork.
At this point in time, it would be well worth getting HVAC-CALC and spending a couple hours measuring walls and getting your own load calculation. If your required tonnage is way different from what was installed, you can proceed arguing with the big-box store knowing that you are right and they were wrong. Build your case solidly and you should better off in every way.
Because of the amount of money involved and the cost of being wrong, I would still work toward getting a pro to do his load calc as well. Then compare it with yours and see where the two differ, and discuss that.
Best of luck -- P.Student
[Edited by perpetual_student on 01-25-2005 at 10:43 AM]
Thanks for the additional comments.
Our house was built 13 years ago, and was part of a Gulf Power Good Cents Home program that was supposed to insure energy efficiency. The ducting is all 1.5" board, rather than the 1" that you see in many houses, and it all appears to be in excellent shape, and well constructed.
The old unit was a 3.5 ton Rheem (that caused me years of grief). The big box store, to their credit, spent quite a bit of time measuring windows, rooms, phases of the moon, etc, and also calculated the load requirement to be 3.5 ton. Their original recommendation was the 14i system, which is available in 3.5 ton, but but I wanted one of the higher efficiency models. The 16i and 19i only come in whole number ton units, so the choice is 3 or 4. As I understand it, the staged compressor (if installed correctly), and variable speed AH should make 4 ton the preferred choice. This is Florida BTW.
No one has measured any airflow in the ducting, and I don't know what the previous Rheem unit was capable of flowing, but it's obvious that the current AH can produce considerably more flow. That's certainly the noise issue, and I'm hoping that can be limited by getting the unit to operate on a lower speed most of the time as I believe it's inteded to do.
I'll be calling Trane in a few minutes, so stay tuned.
I am heartened that the big box store's AC contractor has tried to size the system correctly. In all probability they did not err there. The Florida climate is not terribly different from some parts of S. Texas so we have something in common there. We had some Good Cents home programs here also, in our locale there were some problems with implementation -- the concept was sound but sloppy construction could still spoil things. Texans do *not* tend to be fastidious when it comes to home construction, hope Floridans are better.
To me it seems there are likely issues purely with installation, just as you originally said. Maybe your problems will go away when you find and fix those.
Trane/A-S must have their good reasons for going in 1-ton increments with VS systems. I don't know why but would like to. In your climate there is plenty of reason to pursue high efficiency, as many hours as your system must run during the year.
In the event your duct system is inadequate, I think it is probably something you would want fixed with either system. Return sizing is commonly too small, it was fixed in my house by adding some additional return ducts. Supply duct sizing *can* be too small (as it is in my case) but perhaps there is an obvious way to add capacity without tearing out and rebuilding the whole system.
Manual D is the pro's tool for duct design, it seems this is somewhat more sophisticated than Manual J. I suggest trying to get your contractor to do a Manual D calculation as a possible solution to your problems. Dash works in your state and seems to be an expert and huge advocate of using Manual D, is it possible you could call on him?
Best of luck -- P.Student