Can You Bypass the A/C Gear Motor on a CAT 248B Skid Steer

[MikePhua]

Overview of the CAT 248B Skid Steer
The Caterpillar 248B is a mid-2000s high-flow skid steer loader designed for demanding hydraulic applications such as cold planing, trenching, and brush cutting. With a rated operating capacity of 2,200 lbs and a 76-horsepower diesel engine, the 248B was part of CAT’s B-series lineup, which emphasized improved cab ergonomics, auxiliary hydraulic performance, and simplified service access. Thousands of units were sold across North America and Australia, particularly in rental fleets and municipal operations.
One of the more obscure components on the 248B is the gear motor mounted near the air conditioning compressor. This motor is part of the hydraulic cooling system and is connected to the A/C support bracket, which also houses a breather vent. When this motor fails internally, it can cause hydraulic oil to leak from the breather, creating confusion about the source and severity of the issue.
Symptoms of Gear Motor Seal Failure
Operators have reported the following symptoms:

• Hydraulic oil leaking from the breather vent near the A/C support
  
• Loss of up to one gallon of oil per day
  
• No visible damage to hoses or fittings
  
• A/C system non-functional or unused for years
  
• Gear motor located deep in the chassis, difficult to access
  

The most likely cause is a failed internal seal in the gear motor, allowing pressurized oil to flood the support housing and overflow through the breather.
Terminology Clarification

• Gear Motor: A hydraulic motor that uses gear teeth to convert fluid pressure into rotational motion, often used to drive fans or auxiliary components.
  
• Case Drain Line: A low-pressure return line that allows internal leakage oil from a motor or pump to return to the tank, preventing pressure buildup.
  
• Breather Vent: A pressure-relief component that allows air and excess fluid to escape from a sealed housing.
  
• Solenoid Valve: An electrically actuated valve that controls hydraulic flow based on system logic.
  

Can the Gear Motor Be Bypassed
In theory, yes. If the gear motor is no longer needed—such as when the A/C system is permanently disabled—it may be possible to bypass the motor by looping the hydraulic lines together. This would involve:

• Disconnecting the inlet and outlet hoses from the gear motor
  
• Connecting them directly to each other using a hydraulic-rated coupler
  
• Capping or rerouting the case drain line if present
  
• Ensuring the solenoid logic does not expect feedback from the motor
  

However, this approach carries risks:

• If the motor is part of a cooling circuit, bypassing it may reduce system efficiency
  
• Incorrect line routing could cause pressure spikes or flow restriction
  
• Solenoid-controlled circuits may trigger fault codes or disable other functions
  

Before bypassing, it’s essential to consult the hydraulic schematic for the 248B (e.g., RENR8749) and confirm the motor’s role in the system. Some diagrams show only two lines—pressure in and return out—while others include a third case drain line, which must be handled carefully to avoid backpressure.
Alternative Solution: Replace the Seal
The gear motor seal itself is relatively inexpensive—around $16 USD—and may be accessible without removing the entire motor. If the motor is otherwise functional and the leak is limited to the seal, this is the most cost-effective solution.
Steps to replace the seal:

• Identify the motor part number (e.g., CAT 218-6840)
  
• Order the correct seal kit from a CAT dealer or hydraulic supplier
  
• Drain the hydraulic system and remove the breather housing
  
• Extract the motor or access the seal in place if possible
  
• Replace the seal and reassemble with new O-rings and hardware
  

This approach preserves system integrity and avoids the risks of bypassing.
Field Anecdote and Practical Insight
A technician in Alberta faced a similar issue on a 248B used for snow removal. The A/C had been non-functional for years, and the gear motor began leaking heavily. Rather than bypassing, he replaced the seal and added a small catch can to the breather as a temporary safeguard. The leak stopped, and the machine returned to service without further modification.
This case illustrates that even unused components can affect system performance and that small fixes can prevent larger failures.
Preventive Measures and Recommendations
To avoid future issues:

• Inspect breather vents during routine service for signs of oil saturation
  
• Monitor hydraulic fluid levels weekly, especially in older machines
  
• Replace seals proactively during major service intervals
  
• Keep a copy of the hydraulic schematic for troubleshooting
  
• Label and document any bypasses or modifications for future technicians
  

Conclusion
While bypassing the A/C gear motor on a CAT 248B is technically possible, it should be approached with caution and only after confirming the motor’s role in the hydraulic system. Replacing the seal is often a safer and more sustainable solution. With proper diagnosis and attention to system logic, operators can resolve leaks without compromising machine performance or safety.