Troubleshooting; Heating Mode; Defrosting Mode; Evaporator Coil Temperature Protection - Carrier 38MAQB12-1 Service Manual

Heating Mode

Compressor Running Rules
When T1−Ts>− Δ T, the compressor stops, when T1−TS<
the compressor turns on. Δ T is the programmed parameter of
temperature compensation.
When the AC runs in the MUTE mode, the compressor runs in a
low frequency. When the current is more than setting value, the
current protection function triggers and the compressor stops.
Outdoor Fan Running Rules
The outdoor unit runs at a different fan speed according to T4. For
different outdoor units, the fan speeds are differ.
T4
Fig. 20 – Outdoor Fan Running Rules

Defrosting Mode

The air conditioner enters the DEFROSTING mode according to
the T3 temp. value and the T3 value range temp. change and the
compressor running time. During the DEFROSTING mode, the
compressor continues to run, and the indoor and outdoor motors
stop. The indoor unit defrost lamp displays "

Evaporator Coil Temperature Protection

Off
Decrease
Hold
Resume
Fig. 21 – Evaporator Coil Temperature Protection
When the evaporator temperature temp. is greater than the setting
protection value, the compressor stops.
Refrigerant Leakage Detection
This function is only active in COOLING mode. The function can
prevent the compressor from being damaged by a refrigerant leak
or compressor overload.
Open Condition
When the compressor is active, the coil temperature value of
evaporator T2 either changes very little or not at all.
Δ T−1.5,
E
D
C
B
A
A+
."

TROUBLESHOOTING

This section provides the required flow charts to troubleshoot
problems that may arise.
NOTE: Information required in the diagnoses can be found
either on the wiring diagrams or in the appendix.
Required Tools:
The following tools are needed when diagnosing the units:
S
Digital multimeter
S
Screw drivers (Phillips and straight head)
S
Needle−nose pliers
S
Refrigeration gauges
Recommended Steps:
1 Refer to the diagnostic hierarchy charts below and
determine the problem at hand.
2 Go to the chart listed in the diagnostic hierarchy and follow
the steps in the chart for the selected problem. For ease of
service, the systems are equipped with a diagnostic code
display LED on both the indoor and outdoor units. The
outdoor diagnostic display is on the outdoor unit board and
is limited to a few errors. The indoor diagnostic display is a
combination of flashing LEDs on the display panel on the
front of the unit. If possible, always check the diagnostic
codes displayed on the indoor unit first. The diagnostic
codes for the indoor and outdoor units are listed in the
appendix. Problems may arise that are not covered by a
diagnostic code, however are covered by the diagnostic
flow charts. These problems are typical air conditioning
mechanical or electrical issues that can be corrected using
standard air conditioning repair techniques. For problems
requiring measurements at the control boards, note the
following:
(1.) Always disconnect the main power.
(2.) When possible check the outdoor board first.
(3.) Start by removing the outdoor unit top cover.
(4.) Reconnect the main power.
(5.) Probe the outdoor board inputs and outputs with a
digital multi−meter referring to the wiring
diagrams.
(6.) Connect the red probe to the hot signal and the
black probe to the ground or negative.
(7.) Note that some of the DC voltage signals are
pulsating voltages for signal. this pulse should be
rapidly moving at all times when there is a signal
present.
(8.) If it is necessary to check the indoor unit board you
must start by disconnecting the main power.
(9.) Remove the front cover of the unit and then
control box cover.
(10.) Carefully remove the indoor board from the control
box, place it face up on a plastic surface (not
metal).
(11.) Reconnect the main power and repeat steps 5, 6,
and 7.
(12.) Disconnect main power before reinstalling board to
avoid shock hazard and board damage.
21