Carrier AC question

[dnewton3]

This is why I have a simple single-stage furnace and a/c system. PSC motors and such. No techno-gizmo wizzardry and such.
Simply put: they come on and they turn off based on a singular demand set-point.
As reliable as a chunk of granite.
Very simple to trouble shoot and WAY cheaper to repair in the future.

 

[DBMaster]

Originally Posted By: dnewton3
This is why I have a simple single-stage furnace and a/c system. PSC motors and such. No techno-gizmo wizzardry and such.
Simply put: they come on and they turn off based on a singular demand set-point.
As reliable as a chunk of granite.
Very simple to trouble shoot and WAY cheaper to repair in the future.


I agree. You can still purchase low-end stuff. Not as sexy as the super high SEER rated stuff but seemingly less trouble prone.

 

[Food Scientist]

So I've looked it over as best as I can and it seems everything is hooked up correctly. It's a 24APA324300 model, P=Performance series, 3 = 13 SEER, 24k BTU. The newer model on Carrier's website that has the same specs shows it's a single stage compressor and looking inside the actual unit I can only find one coil.

To KrisZ point, I did trace down the #11 optional connection and the dip switch SW1-2 is turned off.

As I was writing this I think I found the problem. On that set of SW dip switches there are 8 of them, all turned off. On the wiring diagram inside the furnace cover, SW1-2 says Manual switch, low heat only. The diagram also shows switches 4 and 7 are on, which the description is Manual switch, comfort/efficiency Adjustment, and manual switches blower off relay, respectively.

In the thermostat advanced settings for diagnostics, there is a comfort, efficiency, or maximum setting. I tried setting that to maximum earlier to increase fan speed. One of my friends is coming tomorrow so I will run it past him but I'm thinking turning that switch on will allow me to increase the fan speed through the thermostat.

 

[KrisZ]

If the unit is 13 SEER then it's pretty much 100% it is not multistage.

 

[L_Sludger]

How about a programmable thermostat that can learn your A/C system's response time and your at-home hours?

 

[Food Scientist]

So I did change the one dip switch referenced in an earlier post and it did change it a little. The past couple of days have been cool, but just today we were having a small party and the temp started at 73 and rose to 76 over a period of an hour. It's continue to run continuously for a few hours and it's only dropped one degree.

It is a programmable thermostat so yes I could get have the AC come on an hour or two before I would get home. Reading the posts it seems this is how the system is designed, so short of having the system redesigned I will just to learn how to get the house cool when I need it to be.

 

[KrisZ]

Verify that the board is connected to the below diagram for a single stage AC unity, which I'm almost 100% what you have. 2 stage units start from 16 SEER and up I think.
Playing with the thermostat will not achieve much if the furnace fan is wired to the lower speed stage.

 

[Food Scientist]

Just figured out how to upload images from my phone. Tried yesterday to take the thermostat off with no success but as you can see from the photo it's wired completely different than the diagram for the control board. The wires from the thermostat go directly into the comm unit labeled ABCD on the left. The only thing that uses the buss terminals is the humidifier. The wires that go to the blower motor are the 4 pin connector in the background and two other wires on the board.

With the AC on it delivers 800 CFM and off with the fan speed on high it's 1000.

 

[KrisZ]

Here is the Infinity Thermostat manual I found. It may not the the model you have, but the wiring should be the same.
Thermostat manual

From the manual:


Note the two wiring options. One for a communicating AC unit, fig.11 and one for non-communicating AC unit, fig.12, which requires an outdoor temperature sensor, that apparently you have just changed.
To me it looks like the outdoor unit was wired as a communicating unit, which it is not, since a separate temp. sensor was installed and wired in. You will need to figure out which wires are for the thermostat and which ones are for the outdoor unit. You then have to remove the outdoor nit wiring from the ABCD connector and onto the COM and Y/Y2 connections.
If you could provide a clear picture and the wires of the ABCD connector, it would help with identifying the cables.





EDIT:
The unit may in fact be a communicating unit and if that's the case, the ABCD connector should have two wires for each letter. If that's the case I would disconnect the outdoor temp. sensor and see what happens.

 

[Food Scientist]

It has two wires that go into each letter as the first diagram shows. In one of my trials I did unhook the temp sensor and saw no changes. The funny thing is instead of 200 plus degrees, it read 84. Maybe it's a default reading if no OAT is detected. I can try it again when I get home just to be sure and to get a better picture.

 

[KrisZ]

Originally Posted By: SVTCobra
With the AC on it delivers 800 CFM and off with the fan speed on high it's 1000.


If the unit is 3.5 tons, the the dip switch should be in this position, for a 350 CFM per ton rule.

 

[Food Scientist]

I looked it up and there are 12k btus per ton. In an earlier post I found out it's a 24k BTU, so a 2 ton. Seems a little undersized, but the house does have a walk out basement, so great insulation on one side of the house.

So, following the 350cfm per ton, this is supposed to be 700 CFM, which is what is has been until I changed the setting to maximum instead of comfort and increased to 800.

So maybe it is what it is, but I will still look behind the thermostat to see how it's wired. I know that the fan CFM needs to match the requirements of the AC, but slightly warmer air that blows faster seems more cooling than cold air that barely moves.

 

[EA82]

What are the model numbers of both units ? Thermostat is wired the same as the air handler, infinity thermostats can only be wired as 4 wire communicating controllers. Seem like you got an infinity air handler with a performance series condenser instead of infinity condenser.

 

[Food Scientist]

The AC is a 24APA324A300 and the furnace is a 58UVB. 3 = 13 SEER, 24 = 24k BTU, P = Performance series. I couldn't find the exact model for the furnace but says Infinity 96 on the cover and the thermostat is an Infinity.

So yes laserred96gt you are correct.

Could you explain if and why I can't change the blower speed while the AC is on and if that has to do with the 4 wire communication controller?

 

[EA82]

Based on the model number that is a 2 ton unit, by Florida standards that unit is way undersized for a 2400 square ft house, again I'm not familiar with Michigan summers. Your furnace has a variable speed blower motor which ramps up and down based on humidity and demand I believe so there is no set speed to where you can manually change it. I'm not sure if it would make a difference if it ran at a higher speed to be honest with you.
It has been years since I Installed Infinity systems, we always had some type of problem with them so the company steered away from them but certain technician took specific classes to get certified ( which I'm not ).
My guess would be the blower module would be faulty ( common problem ). If you really need to get to the bottom of this I would contact a company to send a tech who understands infinity systems because not every one does.

 

[Food Scientist]

It's 1200 sq ft +- on the main floor and the same for the basement, 1100 sq ft +- finished. The basement is a walkout so at least half of it is insulated by dirt.

For summers up here people complain if it gets above 90, but temperatures below twenty is fairly common, especially in January. So most people (including the previous owners) spend more money on heaters than air conditioners.

The ah ha moment for me as I learn about this stuff is I think it's running as designed. It's a two ton unit, and the chart posted above by KrisZ (who has been very helpful), shows 350 CFM per ton. 2 tons means 700 CFM, which is what it shows in the advanced diagnostics when the unit is running.

I think the bottom line is the unit is undersized by a significant margin for whatever reason, so I just need to learn how to keep it cool as best as I can.

I appreciate everyone's responses of what to check and being this is new to me and obviously not a strong subject of mine, bearing with me on 3 pages worth of discussion.

 

[KrisZ]

I'm glad my posts helped, even though no actual fixing took place, which may be a good thing.

As far as the 2 ton unit being undersized, I don't think it is given that we now know it is single stage and your house really being 1100 sq ft. My house is a two story, 2100 sq ft and my 2 ton unit has no problems maintaining about 75F. It is quite well insulated though.

Single stage units are not meant to knock down the temperature fast. The reason for that is humidity control. An oversized unit, even though will cool faster, will cycle on and off very often and therefore will not pull the moisture out of the air. Also, frequent on/off cycling really shortens the life of the compressor.
A properly sized unit should run about an hour and rest for about ten minutes during the hottest time of the day (early afternoon) and when the temp is in the 90s. This is just to maintain the set temperature. If you ask the system to bring down the temp form 80s to 70s, it will work all afternoon and most of the night to do this.

If your house is over 10 years or older, I would look at refreshing attic insulation and leaky windows. It will improve the comfort and put less load on AC and heat. Investing in insulation yields far better results and on fewer dollars than chasing high efficiency heating and AC, or worse yet, putting a bigger unit.

 

[Food Scientist]

Thank you for the detailed post. I think part of it on my end is that I'm probably used to oversized air conditioners in previous houses, where I can come home and an hour later the AC was caught up. I do remember in the house I moved out of the humidity seemed to be a little high when the AC was on, but that house was a somewhat drafty.

I will definitely look into the insulation, I know the previous owners had insulated it fairly well (even the attic space in the unconditioned garage is insulated), and was built in '88. My buddy that looked at my thermostat also had added insulation to his attic two years ago and said it made a noticeable difference (snow wasn't melting as much from the roof in the winter).

 

[sleddriver]

Originally Posted By: SVTCobra
....The ah ha moment for me as I learn about this stuff is I think it's running as designed. It's a two ton unit, and the chart posted above by KrisZ (who has been very helpful), shows 350 CFM per ton. 2 tons means 700 CFM, which is what it shows in the advanced diagnostics when the unit is running.

I think the bottom line is the unit is undersized by a significant margin for whatever reason, so I just need to learn how to keep it cool as best as I can.
I've been monitoring this interesting discussion and have a few points that may help:

• What type of air filter is installed? Some are very restrictive, especially the higher MERV types. Pull your air filter out temporarily and see if you have more airflow. Also check to see if there might be more than one filter installed, like in a drawer.
  
  Key point being that not all systems have enough pressure headroom to run the filters advertised to block everything. Further, some manufacturers filters are more restrictive than others. 3M filters are less restrictive than Purolator pleated I discovered through research. Some also have the cardboard web on their face, which reduces airflow. Even some brand new pleated filters can be too restrictive for some systems! I learned this while designing a new duct system for my house using ACCA's Manual D.
  .
• Which leads me to my next point, is the duct system too restrictive? Is it flex? If so, is it stretched out? If not, air can swirl inside the metal helix, increasing turbulence which will decrease air flow. Also ensure no flex duct is pinched around a too-sharp-corner. The lower pressure you have to start with, the larger the ducts need to be. This information will be found on the blower table, which plots pressure, CFM, and fan speed.
  .
• Finally, is the evaporator coil clean? Are you able to see the inlet side? If not, you may have to cut a flap door. As all CFM goes through the evap coil, if it's dirty it'll be a MAJOR restriction.

 

[Food Scientist]

Its got a 16X25X4 allergen filter from 3M. I had the same thought that the old filter was so dirty it was impeding the air flow. I took the old one out and it was dirty, and while it was out I tried running the system with no filter and no change. The new filter I put in was another 3M.

Not sure if the duct system is too restrictive - haven't seen any flex ducting and the air isn't coming out really fast or slow, just slow in the sense that it can keep up but if it gets behind then it will take a while. Some places the air comes out faster, but typically they are the vents closest to the blower motor which makes sense as I highly doubt this system is step sized to every part of the house to keep the air velocity the same.

Not sure about the evaporator coil, but when I put my hand on the duct work just down stream it is pretty cold, not leading me to think anything was wrong. The condenser coil outside could use a little cleaning on one side, but isn't completely clogged by any means.