Diagnostic Code Display; Test Mode; Led Lights - Lennox HP21 Unit Information

Latch 2: After the unit operates in low speed for 15
minutes consecutively, it switches to high
speed until low speed demand is satisfied.
Latch 3: After the unit operates in low speed for 30
minutes consecutively, it switches to high
speed until low speed demand is satisfied.
Recall: Used in conjunction with the bypass
button to recall the stored problem codes.
Test: Used in conjunction with the control
button to start test mode.
Latch 2 or 3 modes are recommended in high humidity areas.
If the jumper falls off or is removed, the control will continue to
operate in the previously set mode until the control is reset due
to loss of power, then the control will default to the Normal
mode.

TEST MODE

The control has a test mode. To initiate this mode, move the
jumper to the test position and push the control button. The
unit will operate in low speed for 10 seconds, turn off for ten
seconds, then operate in high speed for 10 seconds. The con-
trol will only go into the test mode if there is no thermostat
demand and 5 minutes has elapsed since the unit ran. The in-
door blower does not run during this mode. The test mode
cannot run more than once every 5 minutes.

LED LIGHTS

Y1 and Y2 lights are connected directly to the inputs from the
thermostat. They indicate low and high speed demand, re-
spectively.
The HI and LO lights are connected directly across the contac-
tor coils. They indicate if the high and low speed contactors are
energized.
The HEARTBEAT light is connected to the microcontroller unit
(MCU). It indicates when the control's MCU is operating cor-
rectly, and also when the control is in delay mode. It blinks at a
rate of four times a second when the MCU is operating proper-
ly and at a rate of once every two seconds when in the delay
mode (such as the 1 or 5 minute delay). If the LED is continu-
ously on or off (assuming the power is on), the MCU is not
operating properly and the control needs to be replaced.
The D1, D2, D4, and D8 (see figure 8) diagnostic lights display
diagnostic codes to aid in unit troubleshooting. Refer to Diag-
nostic Code Table (table 8).

Diagnostic Code Display

A problem code is normally displayed only for the duration of
the error. There is one exception. During a lock out, the code
for the problem causing the lock out flashes once a second
even if the problem condition no longer exists. If other prob-
lems occur during a lock out condition, the codes for those
problems will be saved in memory, but not displayed. The
stored problem codes are displayed by recalling them from
memory. The diagnostic codes can be re-displayed by setting
the jumper to the recall position. The stored codes are dis-
played by pushing the push button. As previously mentioned,
the push button is used to bypass the five-minute delay and to
initiate the test mode. In addition, the button is used to step
back through the stored diagnostic codes and erase the diag-
nostic code memory. Diagnostic codes are recalled in the
reverse order of actual occurrence. Each subsequent button
push will display additional codes until the last one, which will
stay on with additional button pushes. Hold the button down
until the lights go off (approximately five seconds) to erase the
memory. The control has a nonvolatile memory that stores the
63 most recent diagnostic codes. These codes are stored in
memory, even in the event of a power loss.
Not all codes cause lock outs or indicate problems. The pur-
pose of the diagnostic lights is to let the installer or service
technician know what is going on with the entire system, not
just the two−speed control. Some codes do indicate malfunc-
tions or problems with either the control or the HP21, while
others inform the technician of the unit's status. All codes, ex-
cept for three, are stored in memory and may be recalled.
Code 1 − Power Loss for Two Electrical Cycles
This code indicates that the unit's power skipped two elec-
trical cycles (33−40 milliseconds). It may suggest that
power to the unit is dirty" or is of low quality. Code 1 is
stored.
Code 2 − Input Indication
This code indicates that a change has been made and
that the control acknowledges the change. It does not in-
dicate a problem condition. It indicates activity such as
jumper setting changes, delay overrides, or addition of
an optional safety device to Option 1 or 2. Code 2 is not
stored.
Code 3 − Unsteady Thermostat Input
Code 3 indicates intermittent inputs from the room ther-
mostat. Most likely, there is a loose connection at the
thermostat when this condition appears. Code 3 is
stored.
Code 4 − Pressure Switch Opens < Two Minutes
If the low or high pressure switch opens after the compressor
has run for less than two minutes, Code 4 will be displayed.
This may indicate blockage or fan failure. Code 4 is stored. If
the unit still operates after code is displayed, the low pressure
switch stops operation (low pressure is auto−reset). Check for
low system charge.
Code 5 − Pressure Switch Opens > Two Minutes
If the low or high pressure switch opens after the com-
pressor has run for more than two minutes, Code 5 is
displayed. This may indicate an improper charge or coil
obstruction. Code 5 is stored. If the unit still operates af-
ter code is displayed, the low pressure switch stops
operation (low pressure is auto−reset). Check for low sys-
tem charge.
Code 6 − Hot Compressor < Five Minutes
Code 6 indicates the compressor temperature exceed-
ed its limit after running less than five minutes. Code 6
is stored.
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