Carrier weathermaker 8000 fan speed adjustment

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• Central Air blower speed???

1. Central Air blower speed???

   I have a carrier weathermaker 8000 58tua furnace. I believe the blower speed for the ac is set incorrect. I have read that you set blower speed to 400 cfm per ton of cooling and I have a 2 ton system. Right now cooling is set to high speed on the blower which is 1195 cfm. Duct noise has always been an issue with both the returns and supply vents. The heat side is currently using the low and med-low, so the only available speed setting on the blower motor is the med-high. According to the installation manual the med-high setting looks to be about 100 cfm less depending on the external static pressure? Is it worth slowing down the blower to the med-high setting? Other than noise is there anything wrong with having the blower speed set so high? If I use the low speed setting for cooling am I going to have to move the wire back and forth between heating and cooling seasons? Also, I am not going to change the blower speed myself because I know the charge on the ac will need to be adjusted. Thanks for you help!

2. Having blower set too high uses more energy (espcially with undersides ductwork) and you won't remove humidity as well if at all. This makes it a low less comfortable.

   The speed range on PSC motors is somewhat limited. Depending on your static pressure, you may be able to go to med-lo or even lo to get to 800CFM.

   One fairly easy way ot determine the airlfow (when it't not hot inside and outside) is to run the furnace and then measure the temperature rise as close to the furnace as possible after it's run for at least 5 minutes. Then take the BTU's, divide by 1.08 and then by the temp rise and you have CFM. Compare that to the blower speed charts in the data sheets for the furnace. Then assume your static rises a little as the blower speed increases and goes down as speed decreases.

   I don;t see any hardm in Med-hi unless you have extremely restricted ducts. But again, it's possible you my be able to go down to lo speed.

3. It sounds like the blower is inappropriately sized for your cooling needs. However, a good service tech can slow the blower down using low or medium low without any problem, even though the heating uses the same speeds. Carrier/Bryant actually sizes the airflow for their systems at a factory default of 350 CFM/ton, not 400 CFM/ton. So you'd be looking for 700 CFM for your system in an ideal world but 800 CFM would also work. If you have the installation manual for the unit, the fan curve would tell you exactly what speed tap to use to get closest to the desired CFM, based on TESP. Your installing contractor should be able to determine all of those things for you. Or you've got the wrong contractor. That could be a possibility, eh?

   If YOU want change, YOU have to first change.

   If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

4. Here is a chart of blower speeds for my furnace. How can the low blower speed be both used for heating and cooling?

5. Also, this is an existing install in a house that I bought. House has always seemed humid even with the ac set at 72. I have never brought this issue up to my tech. I just want to get all my info together before I give him a call.

6. Any good service tech will know how to make it use the same speed for both heating and cooling.

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INLET

PRESSURE TAP

Fig. 17—Redundant Automatic Gas Control Valve

BURNER FLAME

MANIFOLD

Fig. 18—Burner Flame

c. Adjust air temperature rise by adjusting blower speed.

Increase blower speed to reduce temperature rise. Decrease

blower speed to increase temperature rise.

Disconnect the electrical power before changing the speed

tap. A failure to follow this warning can cause personal

injury.

d. To change blower motor speed selections for heating mode,

remove blower motor lead from control HEAT terminal.

(See Fig. 15.) Select desired blower motor speed lead from

1 of the other terminals and relocate it to HEAT terminal.

See Table 9 for lead color identification. Reconnect origi-

nal lead on SPARE terminal.

Table 9—Speed Selector

COLOR

SPEED

Black

High

Yellow (When

Medium-High

present)

Blue

Medium-Low

Red

Low

White

Common

ON AND

OFF SWITCH

GAS

PRESSURE

REGULATOR

ADJUSTMENT

MANIFOLD

PRESSURE TAP

A95618

BURNER

A89020

FACTORY-

ATTACHED TO

COOL

SPARE

HEAT

FAN

L2

Recheck temperature rise. It must be within limits specified

on unit rating plate. Recommended operation is at midpoint of

rise or above.

The thermostat heat anticipator must be set to match the amp

draw of the electrical components in the R-W circuit. Accurate

amp draw readings can be obtained at thermostat subbase

terminals R and W. Fig. 19 illustrates an easy method of

obtaining the actual amp draw. The amp reading should be

taken after the blower motor has started. See the thermostat

manufacturer's instructions for adjusting the heat anticipator

and for varying the heating cycle length.

NOTE: When using an electronic thermostat, set the cycle rate for

3 cycles per hr.

10 TURNS

EXAMPLE: 5.0 AMPS ON AMMETER

10 TURNS AROUND JAWS

Fig. 19—Amp Draw Check With Ammeter

CHECK SAFETY CONTROLS — The flame sensor, gas valve,

and pressure switch were all checked in the Start-Up Procedures

section as part of normal operation.

1. Check primary limit control.

This control shuts off the combustion control system and

energizes the circulating-air blower motor if the furnace

overheats.

The preferred method of checking the limit control is to

gradually block off the return air after the furnace has been

operating for a period of at least 5 minutes. As soon as the

limit has shut off the burners, the return-air opening should be

unblocked. By using this method to check the limit control, it

can be established that the limit is functioning properly and

operates if there is a motor failure.

2. Check blocked vent safeguard switch.

The purpose of this control is to permit the safe shutdown of

the furnace during certain blocked vent conditions.

a. Disconnect power to furnace and remove vent connector

from furnace outlet collar. Be sure to allow time for vent

pipe to cool down before removing.

20

THERMOSTAT SUBBASE

TERMINALS WITH

THERMOSTAT REMOVED

(ANITICIPATOR, CLOCK, ETC.,

MUST BE OUT OF CIRCUIT.)

HOOK-AROUND

AMMETER

R Y W G

FROM UNIT 24-V

CONTROL TERMINALS

= 0.5 AMPS FOR THERMOSTAT

ANTICIPATOR SETTING

A96316

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