NHTSA ID Number: 11029798
Manufacturer Communication Number: PB_738
TSB/Document Date: 2026-03-06
Summary
Pierce
has implemented two updates to the MCC HVAC system to improve cab air flow and defrost functionality: • Improved windshield defrost vents for MCC HVAC system as a product enhancement • Implemented improved side recirculatory fans for MCC HVAC system as an optional upgrade
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TSB/Document ID: PB_738
Replacement Service Bulletin Number:
MFR Communication Date: 2026-02-11
MFR Internal Campaign ID/Software Version:
Communication Type: Service Bulletin/Repair Instructions
NHTSA Components: UNKNOWN OR OTHER
MFR Component System:
MFR Component Subsystem:
Previous TSB | Next TSB |
Title:
MCC HVAC System Updates
Number:
PB_738
Release Date:
02/10/2026
Revision Number:
Not Applicable
Revision Date:
Not Applicable
Chassis Type:
Saber FR/Enforcer/Velocity/Impel w/ MCC HVAC Systems
Component Description:
MCC defrost vents and side recirculatory fans
Warranty:
See Warranty information listed in each section
Parts:
See parts tables listed in each section
This is a Parts Bulletin. Parts associated with this product upgrade are available for purchase through the dealer
network.
Subject:
Pierce has implemented two updates to the MCC HVAC system to improve cab air flow and defrost functionality:
• Improved windshield defrost vents for MCC HVAC system as a product enhancement
• Implemented improved side recirculatory fans for MCC HVAC system as an optional upgrade
Purpose:
Provide parts/warranty information and installation instructions for the windshield defrost vent and side
recirculatory fan updates.
Procedure:
Command Zone:
The Command Zone software version required for your HVAC system will depend on which updates are being
made to your vehicle(s), please ensure you are purchasing the correct Control Panel for the updates being made:
Parts Information
PN
Description
Kit
Minimum
Software
Version
Required
63-4755-0001 (New)
4437530 (Refurbished)
Control Panel,
HVAC, Rotary Ctrl
v07.19
63-4753-0002
Control Panel,
HVAC, Rotary Ctrl
v07.10
Windshield Defrost Side Recirculatory
Vents
Fans
X
Both
X
X
NOTE: If you want to re-program your own HVAC control panel instead of purchasing a new/refurbished
one, personnel must use the MCC Controller Programming Kit (PN 4022115). Please refer to
SB_588 MCC HVAC Upgrades for detailed instructions on re-programming the HVAC control
panel.
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PARTS BULLETIN #738
Windshield Defrost Vent Enhancement:
WARRANTY: 1-year Basic Apparatus warranty as a product enhancement. Apparatus outside the
warranty period are eligible for parts purchase and installation at customer expense.
PN
Description
Qty
4679417
Plate, Adapter, Louver
A/R
4679392
Windshield Louver
A/R
63-4755-0001 (New)
4437530 (Refurbished)
Control Panel, HVAC, Rotary Ctrl
1
Vents:
NOTE: Note orientation of vent(s) prior to removal to ensure new vent is installed in the same
orientation.
1. Remove two screws (1) and vent (2) from cab (3). Retain screws for installation of new vent.
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PARTS BULLETIN #738
2. Install adapter plate (4) (PN 4679417) and vent (5) (PN 4679392) on cab (3) with two screws (1).
3. Repeat steps 1-2 for remaining vents.
HVAC Control Unit:
NOTE:
• HVAC control panel Command Zone software must be at least v07.19 to ensure proper HVAC
performance and function. Any control panels with previous software versions should be replaced
or updated to at least v07.19.
• Replacement HVAC control panel should look the same as existing but contain updated software.
1. Remove four screws (1) and HVAC control panel (2) from dash (3).
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PARTS BULLETIN #738
2. Check PN on back of HVAC control panel (2) and verify PN is at least 63-4755-0001 (New)/ 4437530
(Refurbished). If your HVAC control panel is older than this, it will need to be replaced.
3. Disconnect connector (4) from HVAC control panel (2).
4. Connect connector (4) to new HVAC control panel (2).
5. Install new HVAC control panel (2) on dash (3) with four screws (1).
Side Recirculatory Fans:
WARRANTY: No warranty coverage as an optional upgrade.
Recirculatory Fan Kits
Chassis
Velocity/Impel
Saber FR/Enforcer
Description
PN
Kit, Defogger, Door Windows
4672889-SVC
Kit, Window Defrost Fan
4529944-SVC
Kit, Defogger, Door Wndws, ST10
3658505-SVC
Kit, Window Defrost Fan
4529944-SVC
NOTE:
• The same wire harness kit (Part # 4529944-SVC) will be used with both the Saber FR/Enforcer
chassis and the Velocity/Impel chassis.
• HVAC control panel Command Zone software must be at least v07.10 to ensure proper HVAC
performance and function. Any control panels with previous software versions should be replaced
or updated to at least v07.10.
• Replacement HVAC control panel should look the same as existing but contain updated software.
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PARTS BULLETIN #738
Velocity/Impel Installation:
Crew cab vents will need to be centered over the crew cab door, then the panel should be marked for drilling.
Front assemblies will have lower mounting holes to be drilled into wire cover and upper holes that share the panel
mounting.
Velocity/Impel Recirculatory Fan Kit (PN 4672889-SVC)
Item No.
Part No.
Description
1
4672891
DEFOGGER,FRT,LH,WLDMT
2
4672893
DEFOGGER,FRT,RH,WLDMT
3
4672894
DEFOGGER,RR,LH,WLDMT
4
4672895
DEFOGGER,RR,RH,WLDMT
5
2822424
FAN 3.0 PUSH,RDL,153,12VDC
6
3250529
LOUVER,DEFROST,FR HEADER
7
82-0257-0002
INSERT,THREADED,.25-20,STEEL
8
82-0418-0002
WASHER,FLAT,NYLON,MOLDED BLACK
9
82-0429-0075
SCREW,.25-20,PH PAN HD,BLKZN
10
82-2039-004
SCREW,#10-24,TORX PN HD TAP
11
82-0428-0075
SCREW,#8-32,PH PAN HD,BLK,ZNC
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PARTS BULLETIN #738
Saber FR/Enforcer Installation:
Crew cab vents will need to be centered over the crew cab door, then the panel should be marked for drilling.
Front assemblies will have lower mounting holes to be drilled into wire cover and upper holes that share the panel
mounting.
Saber FR/Enforcer Recirculatory Fan Kit (PN 3658505-SVC)
Item No.
Part No.
Description
1
3658506
DUCT,WLDMT,DEFOG,FR,SIDE,DS
2
3658507
DUCT,WLDMT,DEFOG,FR,SIDE,PS
3
3658508
DUCT,WLDMT,DEFOG,RR,SIDE,DS
4
3658509
DUCT,WLDMT,DEFOG,RR,SIDE,PS
5
2822424
FAN 3.0 PUSH,RDL,153,12VDC
6
3250529
LOUVER,DEFROST,FR HEADER
7
82-0257-0002
INSERT,THREADED,.25-20,STEEL
8
82-0418-0002
WASHER,FLAT,NYLON,MOLDED BLACK
9
82-0429-0075
SCREW,.25-20,PH PAN HD,BLKZN
10
82-2039-004
SCREW,#10-24,TORX PN HD TAP
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PARTS BULLETIN #738
Wire Harness Installation:
Diagram 60-1420-269A
•
•
The kill switch location will need to be determined by the Dealer and have a label ordered with verbiage
stating that it shuts off the recirculatory fans (Ex: Aux Fan Disable).
o Circuit for lin wire #5255 located behind the HVAC control, mounted to the dashboard.
The ends of the wiring harness will come un-pinned in order to allow for the wire to pass through the hole
that is drilled in order to connect to the fans. Pin connector according to print shown above.
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PARTS BULLETIN #738
Wire Harness Kit (PN 4529944-SVC)
Item No.
Part No.
Description
1
64-4330-H001
WIRE HARN,SIDE WIN DEFROSTERS
2
4225077
MODULE,LIN CONTROLLER,REAR
3
82-2222-0050
SCREW, 10-24, T25 PN HD TFS, SS
4
64-1705-0016
SWITCH,ROCK BLK SPDT,NO CTR PS
N/A
60-1420-269A
WIRING DIA,CAB WINDOW DEF FANS
System Operation:
•
•
•
The speed of the fans will vary, depending on the fan settings from the HVAC control panel.
Any time the standard fans are blowing, the recirculatory fans will also be blowing, unless they are turned
off by the kill switch.
Any time the HVAC is set to DEFROST, the fans will automatically blow at 100%, but may be turned
down from there.
If any additional support is needed, please open a technical support incident on www.pierceparts.com.
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