Toyota Supra MK4 LHD heater box assembly

heater box assembly for a Left-Hand Drive (LHD) Toyota Supra MK4 (JZA80) is a notoriously difficult part to source, as it is mirrored compared to the far more common Japanese (RHD) version. For high-end restorations, finding an intact LHD unit is essential because the plastic casings, internal flap orientations, and heater core piping are not interchangeable with RHD models.

1. Component Breakdown & OEM Part Numbers

The “heater box” is technically a multi-part system consisting of three main housings located behind the dashboard.

• Heater Unit Sub-Assy (The Center Box): Contains the heater core and the blend doors that control air temperature.

  • Part Number: 87010-14030 (Complete unit, though often discontinued as a whole).

• Heater Core (Radiator Unit): The internal heat exchanger.

  • Part Number: 87107-14200 (LHD Specific).

  • Note: Aftermarket copper/brass replacements are highly recommended over original aluminum units, as they resist the common “clogging” issues that plague 2JZ cooling systems.

• Blower Motor & Housing (The Right Box): Located behind the glovebox in LHD cars.

  • Part Number: 87130-14250 (USDM/LHD specific).

• A/C Evaporator Housing (The Middle Box): Sits between the blower and the heater unit.

2. LHD vs. RHD: Why they don’t swap

If you are sourcing parts from a JDM importer, be aware of these critical LHD-specific differences:

• Piping Direction: The heater core inlet and outlet pipes exit the firewall on the left side of the engine bay (near the brake booster) on LHD cars, whereas they exit on the right for RHD.

• Servo Motors: The mounting points for the “Air Mix” and “Mode” servos (which control where the air blows) are mirrored.

• Drain Tube: The condensation drain for the A/C evaporator is positioned to avoid the LHD transmission tunnel and gas pedal.

3. Common Restoration Issues

• Degraded Foam Flaps: Over 30 years, the foam seals on the internal blend doors turn into a sticky black dust that blows out of the vents. When rebuilding a heater box, it is vital to strip the unit and replace these with closed-cell adhesive foam (such as 3M 8153LE) to ensure the defrost and floor vents seal properly.

• Brittle Plastic Mounting Tabs: The “ears” that bolt the box to the dash bar (the large metal pipe behind the dash) are prone to snapping. If you are buying a used unit, always inspect the four main mounting points.

• Heater Control Valve: Located in the engine bay, this valve (Part No. 87240-14150) controls hot water flow into the box. These often seize or leak; if the heater box is out, it is the best time to replace this and the two firewall hoses.

4. Service Tips

• The “Dash Pull”: To remove or service the heater box, the entire dashboard must be removed. This is a 6–10 hour job.

• Pressure Testing: Before installing a used or rebuilt heater box, pressure test the heater core at 1.5 bar (22 psi). Discovering a pinhole leak after the dashboard is reinstalled is a costly mistake.