Sterling MS - Manual (Page 22)

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HIGH LIMIT AND/OR SAFETY LIMIT MAINTENANCE
Single furnace units are equipped with a primary high
limit on the upstream side of the heat exchanger and
a secondary high limit on the downstream side of the
heat exchanger. Multiple furnace units are equipped
with a primary high limit on each furnace section and a
secondary high limit on the downstream unit. The primary
high limit is a disk type switch while the secondary high
limit is a capillary switch. To service or replace high limit
or safety limit:
1. Turn off the manual gas valve and electrical power to
the MS unit.
2. To access the high limits, remove the four screws from
the top of the raceway on each furnace section and
swing the raceway down. The primary limit can be
removed by removing the two screws holding the high
limit bracket to the heat exchanger and removing the
bracket and limit assembly from the heat exchanger.
Note location of and remove wires from limit switch,
then remove push nuts and springs holding limit
switch to bracket. Re-assemble in reverse order
making sure that parts are assembled so that spring
pressure holds limit switch securely against bottom
header plate of heat exchanger.
3. To remove the secondary high limit, remove the wires
from the limit switch, remove the screws and stand-off
sleeves holding the limit switch body to the mounting
plate. Do not remove the screws holding the
mounting plate to the heat exchanger. Slowly pulll
the switch and capillary assembly out of the retaining
tube, taking care to prevent kinking the capillary tube.
Re-assemble in reverse order, careefully pushing the
capillary tube into the retaining tube to prevent kinking
the capillary tube.
4. Complete appropriate start-up procedure as given in
the “Start-Up” section of this manual.
5. Check Burner Adjustment.
6. Check gas control valves and pipe connection for leaks.
7. Check operation of auto gas valve.
8. Check operation of safety devices.
9. Inspect and service blower section of system.
SEASONAL MAINTENANCE
The unit should be thoroughly checked before the start and
at the end of each heating and cooling season.
A. Motors and belts should be inspected.
B. Tighten belts if loose.
C. Check and clean DX or Chilled Water coil twice yearly,
if unit is so equipped per manufacturer’s service
manual. Chilled Water coil must be winterized at
beginning of heating season (i.e. drain water from coil
per manufacturer’s instructions).
D. Check air throughput at beginning of heating season
to confirm unit operation is within the specified
temperature rise range.
E. At beginning of heating season clear Condensate
Drain Pan and P-trap of water if unit is equipped with
DX or Chilled water coil. Clean out drain pan and fi ll
P-trap with a non-toxic glycol solution.
F. Evaporative cooler must be cleaned and maintained
per manufacturer’s instruction frequently during the
operating season.
G. Inspect Control Dampers during periodic maintenance.
Damper pivot points should be cleaned to ensure free
damper operation.
H. Blower wheels should be checked periodically for dirt
build-up on blades. Clean as required.
FILTERS
The fi lter section has been designed to incorporate (as
standard) one-inch washable fi lters. Other optional fi lter
types are also available: two-inch washable throwaways;
or one or two inch hi-effi ciency 30% pleated fi lters.
It is recommended that air fi lters be changed or cleaned
at least four times a year. More frequent attention to fi lters
is required if the air being handled by the unit is unusually
dirty. Air fl ow reduction, caused by the dirty air fi lters, will
increase the discharge air temperature and may cause
unit cycling on the primary limit.
Filters (by others) should be serviced regularly and
changed or washed when necessary to maintain the
required air throughput. In a dusty environment, fi lters
may clog up in less than one month.