blower speed

[mrb8828]

I am having humidity problems with Carrier 5 ton system. House is 2 years old and 2400 sq ft in size (2 story). My system seems to be short cycling anywhere from 8-10 minutes on time and 8-10 minutes off time (during the heat of the day, which is low 90's here in South Texas). The short cycling gets worse at night (3-5 minutes on 10-15 minutes off). The RH inside the house stays at 60-65% with thermostat set at 76-77 (Honeywell Vision 8320-retail version). I was wondering if I could lower blower speed to lower setting without harming system? I have looked at schematics on blower and it says nothing about CFM only that black wire is "high", blue wire is "med/lo", and red wire is "low". From reading posts I know you are looking for 350-400 CFM for max humidity removal. Does anyone know what the CFM is for each speed on my particular system?

Carrier PRODUCT #58STA110-10122
CARRIER MODEL #58STA110-22 (COIL)

INPUT - 110,000 BTU
OUTPUT - 89,000 BTU

ALL THIS WAS TAKEN DIRECTLY OFF LABEL ON UNIT.

THANK YOU GUYS FOR YOUR HELP!

[James 3528]

Yoiu need to solve the short cycle problem and it is not with the blower speed.. 5 tons sounds like a lot. Is the system zoned?

[mrb8828]

Not zoned. Had unit serviced a month ago. Tech told me that unit was slightly overcharged so he removed 1.5 lbs freon. I saw no difference at all as far as humidity removal and the system seemed to struggle with temp on hot days. Called him back out last week and he pumped the freon back in because he did not feel comfortable lowering fan speed. I have closed down all of the registers downstairs to keep cool air off of the thermostat thinking that this is the short cycling problem. But it hasn't helped. I'm stumped!

[James 3528]

One T stat two floors. Never good.

[mrb8828]

I know. Anything I can do with humidity removal or extending run times short of spending a fortune on dampers/baffles etc?

[Panama]

Go ahead and lower the speed a notch and see what happens. Just make sure the evaporator coil doesn't freeze.

Did the tech leave you with his measurements? If so, what were they?

[mrb8828]

First visit readings were:

Head pressure- 195
Suction- 65
Delta- 18 degrees
Superheat- 17 degrees
Subcool- 13 degrees

On second visit he did not document pressures but i did watch him while he was recharging unit and from what i remember the readings on his gauges were 225/45 and the superheat was 1-2 degrees (temp outside was 93 degrees).

He also noted that compressor was operating at max rating of 18.7 amps (actual reading was 18.4)

[James 3528]

45? can't be right.

[mrb8828]

I'm probably giving you an incorrect suction number. I'm pretty sure about the head pressure reading. The reference chart on the condenser called for a 6 degree superheat. He was able to get a 1-2 degree superheat that day. He told me that it would level off in a couple of days but the superheat would be lower with slight overcharge. Sound right? I'm a complete novice when it comes to these things it just seems that unit cannot pull humidity out of house running just 8 minutes at a time.

[Panama]

If I were you I'd get a TXV put on your system. Then you can screw around with blower speeds and get thing just right.

[mrb8828]

Anyone know what the CFM is on med and low fan setting. Schematics on unit don't say what actual CFM is, just high, med, low

[James 3528]

I would see if you can get a additional thermostat and zone the system.

[teddy bear]

Make sure the fan is "auto" setting. Widen the deadband of the t-stat to 3^F. The temp in/out should be 20-25^F difference. Next consider adding dehumidification for the evenings and rainy weather humidity control.

[mrb8828]

My Honeywell Vision thermostat (retail version from Lowe's) won't let me adjust temp swing or cycles per hour. Will I damage compressor by lowering fan speed to medium to increase run time/humidity removal. Hopefully that would bring up split temp 20 degrees or more. I have noticed that my Carrier compressor is very loud when running. It has been this way since I bought the home new two years ago. Are they loud by nature or could there be a problem there?

Thanks!

[casturbo]

I'd lower the fan speed and see how it works for you. But, if the A/H is in the basement and 2nd floor registers are in the ceiling, the lower fan speed may not be able to get the air up there. Evap freezing should no doubt be carefully looked for too.

[mrb8828]

Both furnace and a/c are in an upstairs closet. I was told to listen for a difference in compressor noise as an indicator of whether or not there is additional stress on the compressor due to lowering fan speed. The compressor runs so loudly to begin with that it would be almost impossible to due. Does that sound accurate?

Thanks!

[deanoac]

If the unit is installed vertically or horizontally with a bottom return and maxium ESP of 0.5" W.C. High = 2220, Med-High = 2035, and Med-Low = 1795 cfm. BUT.... you have some other issues with your system, based on what you are telling us either the strainer screen just before the indoor coil metering device is partially restricted or the indoor is sitting in water because the pan is not draining properly, or your indoor coil has a few dead circuits or some combinations of these problems. Either way get the manufactures field technical advisor out with the contactor who installed the system, maybe they can put their heads together and fix the problem before you do anything on your own.