The climate control unit controls the blower
controls, air delivery, and A/C compressor controls
either automatically or semi-automatically. The
control unit receives battery voltage at all times
through fuse 56. With the ignition switch in ON
(II), battery voltage is supplied through fuse 3.
The control unit is grounded at G402.

Fully-automatic Operation

To put the climate control in fully automatic mode,
press the AUTO button and set the fan control
dial to AUTO, then set the desired temperature
by turning the temperature control dial. You will
see FULL AUTO in the system’s display.

The system automatically selects the proper mix
of cooled and/or heated air that will, as quickly as
possible, raise or lower the interior temperature
from its current level to the set temperature. The
system also adjusts the fan speed and changes
direction of air delivery.

When you set the temperature to its lower limit
(60

F/18

C) or its upper limit (90

F/32

C), the

system runs at full cooling or full heating only. It
does not regulate the interior temperature. When
the temperature is set between the lower and
upper limits, the system regulates the interior
temperature to the set value.

Semi-automatic Operation

You can manually select various functions of the
climate control system when it is in FULL AUTO.
All other features remain automatically controlled.
Making a manual selection causes the word
FULL to go off.

However, when you select A/C OFF, the system
cannot regulate the inside temperature if you set
the dial lower than the temperature outside.

Blower Controls

The fan speed is automatically controlled in the
fully-automatic mode. You can manually select
the fan speed by turning the fan control dial
clockwise, just past the AUTO position. This
takes the fan from automatic mode to its lowest
manually controlled speed. Turning the dial
further clockwise increases the fan’s speed,
which increases air flow.

Battery voltage is applied through fuse 37 to the
blower motor relay contacts at all times. With the
ignition switch ON (ll), the blower motor relay in

the under-hood fuse/relay box is energized which
feeds battery voltage to the blower motor. The
blower power transistor controls the blower motor
in all speeds except HIGH. The blower power
transistor is controlled by the climate control unit.
When the control unit requests HIGH blower
speed, it grounds the blower motor HIGH relay
coil, energizing the relay, which connects the
blower motor directly to ground, making the
blower run at high speed.

In cold weather, the blower will not come on
automatically until the heater starts to produce
warm air.

Air Delivery

The climate control unit controls the blower motor
and supplies a 5 VDC reference voltage to the air
mixture control motor.

The air mix and mode control motors each
receive inputs from the control unit. The air mix
motor regulates the mixture of cold and hot air by
varying the position of the heater-evaporator
door. The mode control motor controls the
direction and volume of outlet air. Use the MODE
button to select the vents the air flows from.
Some air will flow from the side vents and the
dashboard corner vents in all modes. Each time
you press the MODE button, the display shows
the mode selected. Press the button four times to
see all the modes. Both the air mix control motor
and mode control motor are grounded by the
control unit.

The recirculation control motor receives battery
voltage through fuse 3 when the ignition switch is
ON (II). It regulates the position of the fresh/recirc
door, and is controlled by two position inputs from
the control unit (“Recirc” and “Fresh”).

A/C Compressor Controls

Voltage is provided at all times to the A/C
compressor clutch relay contacts through fuse 5.
With the ignition switch ON (II), voltage is supplied
to the relay coil through fuse 3.

With the ignition switch ON (II), the climate
control unit grounds the A/C ON input of the PCM
through the A/C pressure switch and the fan
control unit. The PCM then grounds

2004 American Honda Motor Co., Inc.

Circuit Index

▲

▼

▲

▼

–

60-5

HVAC

How the Climate Control Circuit Works

the A/C compressor clutch relay coil. This
energizes the coil, which closes the relay
contacts and provides voltage through fuse 5 to
the A/C compressor clutch. The clutch then
engages and begins turning the compressor. By
default, when the climate control system is on,
the A/C is also on.

Evaporator Temperature Sensor

The evaporator temperature sensor is located on
the evaporator housing. If the temperature at the
evaporator gets too cold, the evaporator
temperature sensor sends a signal to the climate
control unit to turn off the A/C compressor clutch.
This prevents condensation from freezing on the
evaporator fins and blocking air delivery into the
passenger compartment.

A/C Pressure Switch

The A/C pressure switch is located in the
condenser outlet line where refrigerant is in a
high temperature/high pressure liquid state. The
switch will sense abnormally high or low
pressure, and open the circuit. This removes
ground from the PCM, and turns off the
compressor.

Refer to the Service Manual (Section 22,
Automatic Climate Control) for specific tests or
troubleshooting procedures.

2004 American Honda Motor Co., Inc.

Circuit Index

▲

▼

▲

▼