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Old 08-25-2007, 05:55 PM   #1
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Location: Levittown, Pa.
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Two Speed Compressors

Does anyone have a two speed compressor that has the option of changing the speed by the thermostat so that the AC will only run in high speed when the outside temperature reaches 80 to up to 110 degrees. This option may be part of the advanced setup on the new AC units. I have this feature on my "Bryant" system with the Evolution control thermostat.
On my system, this option is called "High Cool Latch".
This feature has not worked to my knowledge when I tried to set it up for 90 degrees last season. It was set up by the installer as "None" which is the default choice which means the AC will run in low speed 80% of the time and only 20% in high speed when high outdoor temperatures exist. Problem is; the high cool latch option and the automatic switchover from low to high does not work.
The regional manager of "Bryant" distributors and the installing dealer should be contacting me to address this problem soon.
The house cools down ok but there is insufficient moisture removal; leaving the house between 58 to 60% relative humidity. It should be at least 50 to 52%.
I like to know if you have this "High Cool Latch" feature and does yours work?

The three technicians that have been at my house to check out the AC system have always told me that everythings ok dispite my discomfort with high humidity. But they are part of the problem as none of them checked out the operation of the electronic circuits that have caused my system not to recognise the demand for high speed or the High Cool latch feature. All they have done is check the low and high side pressures and the amperage.
I guess they are not trained to troubleshoot the control boards of these newer systems.


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Old 08-25-2007, 10:03 PM   #2
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It sounds to me that the unit only works on the higher compressor speed. If the unit were sized properly, and the house is cooling to desired temperature any humidity problems would be indicitative of short run time. How it is supposed to work is that the compressor working at a lower speed would lower the cooling effect and increase the run time to give the ac a chance to remove the humidity before the unit shuts down. If the run time is short you drop room temperature all right, but do not remove the moisture from the air thus raising the relative humidity, as humidity is relative to the temperature. I know that on thermostats and high end humidifiers outside temperature sensors are known to fail. One last thing, if your unit was oversized for your house, your two speed option isn't worth all the extra money it cost because the run time would still be too short on moderate days. Duct mounted dehumidifier is an option to be a sure cure for your humidity problems, but would cost you around 1400 or so installed.


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Old 08-26-2007, 01:32 AM   #3
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My compressor sometimes will run for an hour and the humidity will stay the same at 58 to 60% and my indoor temperature will be 76 degrees. I install those pencil type thermometers in the ductwork and measured the incoming and outgoing temperatures and I get a 14 degree differance. At this differance, there is no moisture removal. But if I force it manually into high speed by lowering the thermostat 5 degrees below its normal set point, then the compressor will kick into high speed after a certain time delay. This will result in a 20 to 22 degree differance and within 15 to 20 minutes, the condensate pump kicks in. After reading the installation manual, I am sure that It is in high speed when I force it. But it does not go into high speed automatically when high outdoor temperatures exist. Some knowlegable people have said that outdoor temperatures have no effect on AC but my system must be differant as it is stated so in the manual and brochure that rising temperatures will make the compressor go into high speed. Recently a technician was here and I told him that the only way I can get a comfortable house is by forcing it into high speed and he said that is not a good idea.

The circuit board develops a history of the operation of the cooling system and forcing it may cause problems. I don't believe that; as it is normal for anyone to lower their thermostats if they feel uncomfortable.

But you do have a point about low speed being better for moisture removal, but my system does not remove it in low speed. The installer and the regional mananger for "Bryant" will be contacting me this week to solve this problem.

The system started to have problems with moisture removal only after two months after installation and every time I complained, the technician said its working ok for him. But they are only checking the suction and high pressure sides and the amperage and nothing else.

As I type this, I check the thermostat service menu and here is some data in case it may help you understand my situation:
Cool Stage - Low Speed.
Airflow CFM - 430.
Coil Temp. - 89 degrees.
Blower rpm - 495.
Static Pressure - 0.16
The room temperature is now 76 degrees at 62% relative humidity.

I used to have a 2-1/2 ton system and had simular problems with moisture removal and the present system is 2 tons. I have approximately 1500 square feet of living space. All the neighbors have either a 2-1/2 or a 2 ton system.

Last edited by rjordan392; 08-26-2007 at 01:38 AM.
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