Low cooling, suspect slow blower

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Old 06-19-06, 08:24 AM
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Low cooling, suspect slow blower

In moderate heat (90 degrees) the air conditioning will bring the temperature down at a rate of only 1 to 2 degrees per hour. This problem is going into the third year. To keep the house cool we must "catch it" on the way up and have the system run all day. When the compresssor starts the house fan has a small speed increase, but I don't think it is sufficient. Here is why.

All filters are recent and clean.
The cooling coils have been cleaned.
There is an 18-20 degree drop between the intake and the return vents.
At the annual service I am told the freon pressures are good. (They can't figure out the problem.)
When the heater is used the blower is quite strong.

When originally installed the system (Rheem) ran great, and would bring temperatures down at 5 degrees in a half hour. If my guess is correct, how do I test the blower and/or the controller? A replacement board is $225, so I don't want to just start replacing things.
 
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Old 06-20-06, 06:52 PM
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The temp drop is a good range. Don't want any less.

This a variable speed furnace? Model #

5 degrees drop in a half hour is NOT an ideal drop. 1 degree in a hour is good.
 
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Old 06-22-06, 08:22 PM
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The furnace / air handler is a Rheem Criterion II. Actual model number is RC8A-4882GH218. Yes, mutliple discreet fan speeds. At a minimum we have low, medium high, and high. There may be a couple other speeds available, it has been a while since I examined the control board. From what I can tell from the schematic and the board taps, "cool" should give you the highest fan speed, but that seems to come with a request for heat.

Only 1 degree per hour? That would hardly seem adequate to cool down a hot house.
 
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Old 06-22-06, 08:55 PM
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A fast cool down will not dehumidfy your home, then it leads to a clamy feeling. When you feel that way, you turn down the t-stat to get the house cooler to feel cooler. The guys on here will agree with me. 5 degrees in half hour is NOT ideal.


I'd check to make sure the wires are hooked up right on the board.

Heating should be low or med low.

Cooling should be Med high (about 17 to 20 degree drop)
 
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Old 06-23-06, 07:45 AM
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For us, humidity is only an occasional problem. (Southern California.)

The control board has several taps for the blower, each one labeled with a different speed, cool being the highest. Feeling the air flow at the vents, the "cool" speed definitely was not the highest. My guess was that the board normally put voltage to two or more of the taps to get that high speed but something had failed and was now only putting voltage on one of the taps. Without knowing for sure how it is supposed to work, it is hard to figure out how to test my idea.

I will call for service help and tell them I need someone who can troubleshoot a bad control board. Thanks for the help.

"There are no failed experiments, only unexpected results."
 
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Old 06-23-06, 08:35 AM
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Voltage will only come out of one tap. 120 volts. So on a call of cool or fan "ON" at t-stat, the cool tap should only be powered.


In heating mode, the heat tap should only have power of 120 volts.

Most fan wire is

Black= high speed
Brown or Yellow=med speed
Red-= Low

I have seen wires get turned around on the heat/cool taps. Make sure the right speed is on the right tap.
 
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Old 06-25-06, 12:08 PM
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I think the motor wires are properly connected, but I will check them again. Reading the problems of other members makes me wonder if somehow the thermostat wiring is wrong. Wires mis-connected so that a call for heat gets the furnace and high blower, while a call for cool gets the compressor and low blower. Is this possible? Where would I find a diagram that shows the correct connection at both ends, thermostat and air handler?
 
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Old 06-25-06, 01:57 PM
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unit can't cool space

if td across coil is 18 to 20 degrees. and if the suction line is cold(larger insulated line) unit is to small for the space. look at attic insulation, attic ventilation. what changed in the building ,as for as building load. also is filter clean, blower wheel clean and how is the air flow fron the vents
 
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