SERVICING
S-200 CHECKING EXTERNAL STATIC PRESSURE
The minimum and maximum allowable duct static pressure is found in the Technical Information Manual.
Too great of an external static pressure will result in insuffi- cient air that can cause icing of the coil, whereas too much air can cause poor humidity control, and condensate to be pulled off the evaporator coil causing condensate leakage. Too much air can cause motor overloading and in many cases this con- stitutes a poorly designed system. To determine proper air movement, proceed as follows:
1.Using a draft gauge (inclined manometer) measure the static pressure of the return duct at the inlet of the unit, (Negative Pressure).
S-201 CHECKING TEMPERATURE RISE
Temperature rise is related to the BTUH output of the unit and the amount of air (CFM) circulated over the indoor coil.
All units are designed for a given range of temperature increase. This is the temperature of the air leaving the unit minus the temperature of the air entering the unit.
The more air (CFM) being delivered through a given unit the less the rise will be; so the less air (CFM) being delivered, the greater the rise. The temperature rise should be adjusted in accordance to a given unit specifications and its external static pressure.
1.Take entering and leaving air temperatures.
2.Select the proper speed tap from the unit's blower perfor- mance data in the Technical Manual for the specific unit.
3.Take motor amperage draw to determine that the motor is not overloaded during adjustments.
Total External Static
2.Measure the static pressure of the supply duct, (Positive Pressure).
3.Add the two readings together.
NOTE: Both readings may be taken simultaneously and read directly on the manometer as shown in the illustration above, if so desired.
4. Consult proper table for quantity of air.
If the external static pressure exceeds the minimum or maxi- mum allowable statics, check for closed dampers, dirty filters, undersized or poorly laid out ductwork.
T
T
RISE = TSUPPLY 
Checking Temperature Rise
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