Cabin Heater Module (Chm) & Heater Booster Module; (Hbm); System Description - Mercedes-Benz Sprinter 2003 Manual

Compres SO Accel (Compressor Shut Off - Due
To Acceleration)
The Engine Control Module transmits this data. A
status of YES indicates that the compressor shut
off because of an acceleration request. A status of
NO indicates that there is no acceleration request.
If shut off due to an acceleration request, the
compress will switch on again after 20 seconds. In
addition, the original acceleration request can no
longer exist for the ECM to acknowledge a subse-
quent request. In the event of a CAN Bus commu-
nication failure, NO is displayed as a substitute
value.
Compres SO W/E-Off (Compressor Shut Off -
Due to Emergency Off)
The Engine Control Module transmits this data. A
status of YES indicates that the compressor shut
off because of an emergency off request. A status of
NO indicates that there is no emergency off re-
quest. In the event of a CAN Bus communication
failure, the last stored value is displayed as a
substitute value.
Auxiliary Fan
The ATC Module transmits this data. A status of
ON indicates that the auxiliary fan is operational.
A status of OFF indicates that the auxiliary fan is
not operational. The Auxiliary Fan normally oper-
ates when refrigerant head pressure exceeds 290
PSI and coolant temperature exceeds 221°F. In the
event of a CAN Bus communication failure, 257°F is
displayed for coolant temperature (in Sensors) and
the Auxiliary Fan will run continuously.
Light PB CTRL Module
This input displays a status of Bright for positive
dimmer switch operation and Dimmed for nega-
tive dimmer switch operation. In the event of a CAN
Bus communication failure, Bright is displayed.
3.3.2 CABIN HEATER MODULE (CHM) &
HEATER BOOSTER MODULE (HBM)

3.3.2.1 SYSTEM DESCRIPTION

WARNING: NEVER OPERATE THE HEATER
IN AN ENCLOSED AREA THAT DOES NOT
HAVE EXHAUST VENTILATION FACILITIES.
ALWAYS VENT THE HEATER'S EXHAUST
WHEN OPERATING THE HEATER. REFER TO
VENTING THE
BELOW FOR PROPER EXHAUST VENTING
INSTRUCTIONS. FAILURE
THESE INSTRUCTIONS CAN RESULT IN
PERSONAL INJURY OR DEATH.
HEATER'S EXHAUST
TO FOLLOW
GENERAL INFORMATION
WARNING: ALLOW THE HEATER ASSEMBLY TO
COOL BEFORE PERFORMING A COMPONENT
INSPECTION/REPAIR/REPLACEMENT.
TO FOLLOW THESE
RESULT IN PERSONAL INJURY OR DEATH.
WARNING: ALWAYS
VEHICLE'S BATTERY
PERFORMING ANY TYPE OF WORK ON THE
HEATER ASSEMBLY. FAILURE TO FOLLOW
THESE INSTRUCTIONS CAN RESULT IN
PERSONAL INJURY OR DEATH.
WARNING: NEVER ATTEMPT TO REPAIR THE
HEATER ASSEMBLY
INTERNAL COMPONENTS.
PERFORM HEATER
REPLACEMENT IN ACCORDANCE WITH THE
SERVICE INFORMATION.
FOLLOW THESE
RESULT IN PERSONAL INJURY OR DEATH.
CAUTION: Always
Pre-Test (In The Diagnostic Procedures) Prior
To Performing Any Other Test On The Heater
For The Test Result To Be Valid.
NOTE: Do not disconnect the vehicle's
battery or the heater's main power-supply
while the heater is in operation or in
run-down mode. Failure to follow these
instructions may result in excess emissions
from the heater.
NOTE: Failure to prime the Dosing Pump
after draining the fuel line will prevent heater
activation during the first attempt to start the
unit. This may also set a Diagnostic Trouble
Code (DTC) in the control unit's memory. Do
not perform the Dosing Pump Priming
Procedure if an attempt was made to start the
heater without priming the Dosing Pump
first. This will put excess fuel in the heater
module and cause smoke to emit from the
heater's exhaust pipe when heater activation
occurs.
NOTE: Waxed fuel can obstruct the fuel line
and reduce flow. Check for the appropriate
winter grade fuel and replace as necessary.
The Cabin Heater Assembly and Heater Booster
Assembly are supplemental type heaters designed
to pre-heat the engine's coolant in order to supply
the vehicle's occupants with heat prior to the engine
7
FAILURE
INSTRUCTIONS CAN
DISCONNECT THE
PRIOR TO
OR ANY OF ITS
ALWAYS
COMPONENT
FAILURE TO
INSTRUCTIONS CAN
Perform The Heater