GMEC96 Service Manual

SYSTEM OPERATION
37
SINGLE COOLING STAGE THERMOSTAT OR 2ND
STAGE COOLING MODE SEQUENCE.
· On a call for cool, the Y and G thermostat contacts
close signaling the control module.
· The LED will display a “GREEN”2 flash
· The compressor and condenser fan are energized. The
compressor is connected to the Y terminal of the con-
trol module.
· The circulator fan is energized at cool speed after a
cool on delay. The electronic air cleaner will also be
energized.
· After the thermostat is satisfied, the compressor is
de-energized and the Cool Mode FanOff Delay period
begins.
· Following the 60 second Cool Mode Fan Off Delay
period, the cool circulator and air cleaner relay are
de-energized
MANUAL FAN ON:
· On a call for Fan, the G thermostat contacts close
signaling the control module.
· The LED will display a solid “GREEN”
· When a call for G is received, the control will energize
the circulator in low heat speed after the fan on delay
time expires. The electronic air cleaner will also be
energized at this time.
· When the thermostat fan switch is moved to the ON
position, the circulator blower is energized at low heat
speed and the electronic air cleaner is also energized
· When the thermostat fan switch is moved back to the
AUTO position, the circulator fan and air cleaner relay
are de-energized and the control awaits a thermostat
call for heat or cool.
· Exception: During the Cool “On”delay, the control will
not respond to the fan input. If the fan was called prior
to the call for cool, the circulator will remain ener-
gized during the Cool “On”delay.
· If the fan is called prior to a call for heat, the circulator
will remain energized during the entire call for heat
sequence.
Combustion Quality
Combustion quality can be affected by several factors. Major
factors are venting and draining.
Venting
The venting system should be planned and installed with
the following in mind;
• Should not be longer than necessary
• Use 45°elbows rather than 90° elbows when possible
• Must not sag or otherwise trap condensate
• Use longest radius fittings possible
• If using 3" venting, make the transition from 2" to 3"
as close as practically possible
• Make sure there is no flue gas recirculation into the
combustion air pipe
Condensate Drainage
Furnace combustion can be affected if a furnace is holding
condensate. Check for proper connections of drain hoses,
make sure furnace condensate trap is clean. Make sure
furnace is not improperly sloped. Make sure air condition-
ing coil drain is not interfering with furnace drain.
Other Causes
1. Manifold Gas Pressure must be set for the gas being
used, Natural or L.P., high and low firing rates. If con-
verted to L.P. gas, check size of all orifices
2. Remove Draft Inducer, Check the integrity of the gasket
between the inducer and the collector box cover, any air
leak here will have a negative effect on combustion.
Check the orifice hole in the collector box, it must be
free of burrs on both sides
3. Make sure burners are clean, not out of position and line
up correctly with exchanger tubes, including the heat
exchanger orifice plate between the burners and the heat
exchanger tubes, make sure it is not loose, missing a
screw or hanging down between the burners and heat
exchangers causing flame impingement.
4. Make sure the field installed gas line is not binding and
causing distortion of burner assembly
5. If the furnace is installed as a one pipe system; make
sure the surrounding area and structure are adequate to
provide combustion air
6. Make sure there are no cabinet air leaks allowing supply
air to affect combustion
7. If heat exchanger integrity is uncertain, follow procedures
in Service Bulletin SF-041