Frequently Asked Questions About Kenworth W900A Heat & AC Parts

Will these heat and AC parts fit my specific year W900A, and what are the main differences between model years?

Most heat and AC components for the W900A are compatible across the 1961-1985 production years, but there are some important distinctions. Pre-1973 models often use different heater box configurations and control valve setups compared to 1973-1985 models. Always verify your truck's VIN and model year before ordering. Key differences include: early models (1961-1972) typically have manual cable-operated controls, while later models may have vacuum-operated systems. Compressor brackets and mounting points also varied between engine options like Cat 3406, Cummins Big Cam, and Detroit Diesel.

What are the most common installation challenges when replacing W900A heater cores or AC components?

The biggest challenge is accessing the heater box, which requires removing the glove box and potentially loosening the dash panel. Heater core replacement typically takes 3-4 hours. Common issues include: seized heater control valves that need to be replaced along with the core, deteriorated foam seals that should be replaced to prevent air leaks, and rusted mounting brackets. For AC work, evacuating and recharging the system requires proper equipment. Many customers report difficulty routing new heater hoses through the firewall - using silicone spray and pre-bending hoses helps significantly.

How do I know if I need R12 or R134a AC components, and can I convert my system?

W900A trucks originally came with R12 systems. If your truck hasn't been converted, you'll see R12 fittings (smaller, threaded) and a mineral oil compressor. R134a conversions are common and recommended since R12 is no longer produced. Conversion requires: new O-rings, receiver-dryer, expansion valve, and PAG oil-compatible compressor. The condenser and evaporator can usually be retained if in good condition. Converted systems typically cool about 85-90% as well as original R12. Always use barrier hoses rated for R134a to prevent refrigerant loss.

What's the quality difference between OEM and aftermarket heater motors and blower assemblies?

OEM-style replacement motors from manufacturers like Red Dot and Bergstrom typically last 8-10 years with proper maintenance. Budget aftermarket motors often have lighter-duty bearings and may only last 2-3 years in commercial use. Key quality indicators: look for sealed ball bearings rather than sleeve bearings, metal fan cages instead of plastic, and motors rated for continuous duty. Higher-quality units draw 15-20 amps at full speed versus 25+ amps for cheaper alternatives, reducing electrical system strain. The price difference is usually $40-60 but saves repeated replacements.

Which heater control valves work best, and how do I prevent them from sticking or leaking?

Cable-operated brass valves are most reliable for W900A applications, with brands like Heater Craft and Red Dot offering the best longevity. Avoid plastic-bodied valves as they crack under hood heat. Common failure points: the valve seat wears and won't fully close, causing constant heat, or corrosion prevents the valve from opening. Prevention tips: flush cooling system annually to prevent debris buildup, use a 50/50 coolant mix to prevent corrosion, and exercise the valve monthly during summer months. When replacing, also install new control cables as stretched cables are often the real culprit behind "stuck" valves.