3.3.8
Heat pump heating mode –
Modulating thermostat, outdoor unit
two stage
• First stage (low) heating: Thermostat closes cir-
cuits R to G and R to Y1.
Furnace delivers low stage heating airflow.
• Second stage (high) heating: Thermostat closes R
to G, R to Y1 and R to Y/Y2. Furnace delivers high
stage heating airflow.
WARNING
E
LECTRICAL SHOCK OR UNIT DAMAGE HAZARD
Failure to carefully read and follow this WARNING
could result in equipment malfunction, property
damage, personal injury and/or death.
Disconnect power to unit before removing or re-
placing connectors or servicing motor.
Wait at
least five (5) minutes after disconnecting power
before handling.
3.4
AIRFLOW VERIFICATION
Verify the airflow by taking readings of the following
points, while the elements are in heating mode:
a) Total amperage of all the heating elements;
b) Voltage at the furnace;
c) Supply air temperature. The point of the reading
must not be affected by radiant heat from the ele-
ments;
d) Return air temperature.
From these readings, one can arrive at an approximate
calculation of the average airflow. To do that, the follow-
ing formula should be used:
Liter/s
=
0
.
82
×
amps.
×
volts
Diff. temperature °C
CFM
=
3
.
1
×
amps.
×
volts
Diff. temperature °F
Tables 3 and 4 show estimated airflows for various
temperature rises.
3.4.1
Supply Air Temperature Rise Test
1. Operate the unit at maximum power for at least 10
minutes;
2. Measure the air temperature in the return air
plenum;
3. Measure the air temperature in the largest trunk
coming off the supply air plenum, just outside the
range of radiant heat from the heat exchanger. 0.3
m (12”) from the plenum of the main take-off is usu-
ally sufficient;
4. Calculate the temperature rise by subtracting the
return air temperature from the supply air tempera-
ture.
If the temperature rise exceeds the temperature spec-
ified in Table 2 by 5°F/2.8°C, move the “AC/HP
CFM ADJUST” black wire to high (HI) position.
If the excessive temperature rise cannot be re-
duced by increasing fan speed, investigate for duct-
work obstructions or dirty and improper air filter.
CAUTION
It is important to check the airflow and to ascer-
tain that the unit does not operate above the tem-
peratures specified in the Technical Specifications
(Table 2). This is particularly important if a cool-
ing coil or a heat pump has been installed in the
ducts.
Hi-Limit thermal protectors should never need to
engage during the normal functioning of the appli-
ance. They are strictly designed to engage during
the improper functioning of the blower or when the
filter was improperly maintained.
3.4.2
High limit verification
After operating the furnace for at least 15 minutes, restrict
the return air supply by blocking the filters or the return air
register and allow the furnace to shut off on High Limit.
The electric heaters must deactivate themselves before
the warm air temperature exceeds 200°F (93°C).
Remove the obstruction and the elements should restart
after a few minutes.
4
MAINTENANCE
WARNING
E
LECTRICAL
S
HOCK HAZARD
Turn OFF power to the furnace before any disas-
sembly or servicing.
Failure to do so can result in death, bodily injury
and/or property damage.
Preventive maintenance is the best way to avoid unnec-
essary expense and inconvenience. Have your heating
system inspected by a qualified service technician once
a year. Do not attempt to repair the furnace or its con-
trols. Call a qualified service technician.
Before calling for repair service, check the following
points:
1. Check fuses or the circuit breakers;
2. Check if the 15 A circuit breaker on the furnace is
disengaged;
3. Check if the 5 A fuse of the control board is blown;
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