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As an example, if local codes require 10% outdoor air during
occupied conditions, outdoor-air temperature is 60 F, and
return-air temperature is 75 F:
(60 x 0.10) + (75 x 0.90) = 73.5 F
Carefully adjust the unoccupied minimum position until the
measured supply-air temperature matches the calculated
value. Then, carefully adjust the occupied minimum position
set point on the controller until the desired position is
reached.
D. Heating, Units with Economi$er+
When the room temperature calls for heat through terminal
W1, the indoor (evaporator) fan contactor (IFC) and heater
contactor no. 1 (HC1) are energized. On units equipped for
2 stages of heat, when additional heat is needed, W2 is ener-
gized and the high-fire solenoid on the main gas valve (MGV)
is energized. The economizer damper moves to the minimum
position. When the thermostat is satisfied, the damper
moves to the fully closed position.
SERVICE
I. CLEANING
Inspect unit interior at the beginning of heating and cooling
season and as operating conditions require.
A. Evaporator Coil
1. Turn unit power off and install lockout tag. Remove
evaporator coil access panel.
2. If economizer or two-position damper is installed,
remove economizer by disconnecting Molex plug and
removing mounting screws.
3. Slide filters out of unit.
4. Clean coil using a commercial coil cleaner or dish-
washer detergent in a pressurized spray canister.
Wash both sides of coil and flush with clean water.
For best results, back-flush toward return-air section
to remove foreign material. Flush condensate pan
after completion.
5. Reinstall economizer and filters.
6. Reconnect wiring.
7. Replace access panels.
B. Condenser Coil
Inspect coil monthly. Clean condenser coil annually, and as
required by location and outdoor air conditions.
One-Row Coils (Size 036)
Wash coil with commercial coil cleaner. It is not necessary to
remove top panel.
2-Row Coils (Sizes 048-073)
Clean coil as follows:
1. Turn off unit power and install lockout tag.
2. Remove top panel screws on condenser end of unit.
3. Remove condenser coil corner post. See Fig. 37. To
hold top panel open, place coil corner post between
top panel and center post. See Fig. 38.
4. Remove screws securing coil to compressor plate and
compressor access panel.
5. Remove fastener holding coil sections together at re-
turn end of condenser coil. Carefully separate the
outer coil section 3 to 4 in. from the inner coil section.
See Fig. 39.
6. Use a water hose or other suitable equipment to flush
down between the 2 coil sections to remove dirt and
debris. Clean the outer surfaces with a stiff brush in
the normal manner.
7. Secure inner and outer coil rows together with a field-
supplied fastener.
8. Reposition the outer coil section and remove the coil
corner post from between the top panel and center
post. Reinstall the coil corner post and replace all
screws.
C. Condensate Drain
Check and clean each year at start of cooling season. In win-
ter, keep drain dry or protect against freeze-up.
D. Filters
Clean or replace at start of each heating and cooling season,
or more often if operating conditions require it. Replacement
filters must be same dimensions as original filters.
E. Outdoor-Air Inlet Screen
Clean screen with steam or hot water and a mild detergent.
Do not use disposable filters in place of screen.
CAUTION: When servicing unit, shut off all electri-
cal power to unit and install lockout tag to avoid shock
hazard or injury from rotating parts.
Fig. 37 — Cleaning Condenser Coil
Fig. 38 — Propping Up Top Panel