54-083

HVAC Software Updates
4700
4800
4900
5700

Western Star
Service Bulletin

6900
> 47X
> 49X

General Information
This service bulletin describes heating, ventilation, and air conditioning (HVAC) controller software updates
released on January 4, 2022 that affect the 47X and 49X HVAC system. This software update provides
resolutions to the following three conditions.
• Sleeper vehicles with Battery Powered HVAC System (BPHS) do not turn on the engine fan when using
the engine air conditioner compressor.
• Sleeper vehicles with optimized idle (O/I) blows hot air when parked.
• When running in full A/C mode, economy (ECO) mode automatically turns on after 45 minutes.
Only the forward control unit (FCU) and axillary control unit (ACU) software changes are affected. For
reference, the parked control unit (PCU) software update is included in Table 1. These software changes are
available for service updates and are backwards compatible.
DiagnosticLink Software Updates
FCU
ACU
21.28.01
21.28.01
001 448 09 28 ZGS 001
001 448 12 28 ZGS 001

Controller
SW Version
SW Part Number

PCU
20.35.1
000 448 70 28 ZGS 007

Table 1, DiagnosticLink Software Updates

This version of the HVAC controller software contains three changes that affect HVAC operation. See Table 2.

Item
Affected vehicles: 49X
Sleeper vehicles with BPHS
running under very specific
conditions do not turn on the
engine fan when using the
engine A/C compressor.

HVAC Operation Changes
Symptom
Conditions of Occurrence
A/C cooling is diminished
Specific conditions when the
when running in this
engine fan does not engage
condition.
include the following. *

• Engine running in
parked HVAC and A/C
request coming from
ACU

Resolution
FCU and ACU software
updates listed in Table 1
correct this issue and allows
the engine fan to turn on with
an ACU A/C request.

• Not in Optimized Idle
(O/I)

• Parking brake is set
• FCU not in A/C
Affected vehicles: 49X
Sleeper vehicles with O/I
blows hot air when parked.

request mode (A/C or
defrost)
When the HVAC is running in Engine is in auto elevate with
O/I in comfort mode, if
CPC software version 20.1 or
programmed for auto elevate earlier and O/I is running in
feature and auto elevate
comfort mode.
activates, the HVAC blows
hot air.

Western Star Service Bulletin, 06/21/2022

FCU and ACU software
updates described in Table 1
correct this issue and
eliminates auto elevate from
blowing hot air when running
in O/I comfort mode.

Page 1

54-083

HVAC Software Updates

Western Star
Service Bulletin

Item
Affected vehicles: 47X and
49X
LED display located in the
FCU A/C button turns from
blue to green after 45
minutes of operation. Figure
1 shows the LED in full A/C
mode.

4700
4800
4900
5700

6900
> 47X
> 49X

HVAC Operation Changes
Symptom
Conditions of Occurrence
When selecting full A/C mode Occurs after the center A/C
button is pressed.
(maximum cooling), the
system automatically reverts
to ECO mode after 45
minutes, causing cabin
temperature to possibly
increase.

Resolution
With the release of the FCU
software 21.28.01, parameter
A0174479928-002 Manual
ECO MODE allows the driver
to maintain full A/C mode
without the system
automatically placing the
controller back into ECO
mode after 45 minutes.

* A/C logic provided by FCU software turns off the A/C clutch if pressure is too high

Table 2, HVAC Operation Changes

Figure 1 shows the A/C compressor LED illuminated in full A/C mode (blue). When ECO mode is engaged, the
LED illuminates green.

04/18/2022

f832249

Fig. 1, AC Compressor LED Display

Figure 2 shows the Par_HVAC_Controller_ECO_MODE parameter (A0174479928-002 Manual ECO Mode)
used to turn off automatic ECO mode.

05/19/2022

f121196

Fig. 2, Par_HVAC_Controller_ECO_MODE Parameter

Page 2

Western Star Service Bulletin, 06/21/2022

HVAC Software Updates
4700
4800
4900
5700

6900
> 47X
> 49X

54-083
Western Star
Service Bulletin

Warranty
This is an informational bulletin only. Warranty does not apply.

Western Star Service Bulletin, 06/21/2022

Page 3