Locating and Maintaining the A/C Drain Hose on a Caterpillar D6R Dozer

[MikePhua]

Cab Water Intrusion Caused by Blocked Drainage
Operators of the Caterpillar D6R series dozers occasionally encounter a frustrating issue: water pooling inside the cab due to a blocked or misrouted air conditioning drain hose. This problem is especially common in humid environments or after extended idle periods, when condensation from the evaporator has nowhere to escape. Instead of draining outside the machine, excess moisture seeps into the cab floor, soaking insulation and creating mold risks.
The D6R, a mid-size track-type tractor introduced in the late 1990s, is widely used in earthmoving, forestry, and mining. With an operating weight of approximately 45,000 lbs and a net power rating of 200–215 hp, it remains a staple in Caterpillar’s dozer lineup. The D6R II variant, in particular, features an enclosed cab with integrated HVAC systems, making proper drainage essential for operator comfort and equipment longevity.
Drain Hose Location and Identification
On the D6R II (serial prefix ADE), the A/C drain hose is connected to the bottom of the evaporator box inside the cab. Two hoses typically exit this box:

• One hose routes condensate water to the exterior of the machine
  
• The second may serve as a pressure equalizer or secondary drain, depending on configuration
  

The primary drain hose is often located on the right-hand side of the evaporator housing. It exits through a grommet or bulkhead fitting and should discharge water beneath the cab or onto the track frame. If this hose is blocked, disconnected, or pinched, water will back up into the cab.
Common Causes of Blockage

• Mud dauber nests or insect debris inside the hose
  
• Dust accumulation from long-term operation in dry environments
  
• Kinked hoses due to improper routing or cab modifications
  
• Disconnected fittings during HVAC service or filter replacement
  

Technicians report that the open end of the secondary hose is particularly vulnerable to insect intrusion. In one case, a dozer parked near a swamp developed a complete blockage from a hardened mud nest, causing water to overflow into the footwell.
Inspection and Cleaning Procedure
To restore proper drainage:

• Remove the cab floor panel or HVAC access cover to expose the evaporator box
  
• Locate the arrow-marked hose connection at the bottom of the housing
  
• Disconnect the hose and inspect for debris or obstructions
  
• Use compressed air or a flexible wire to clear the line
  
• Flush with warm water and mild detergent if buildup is severe
  
• Verify that water flows freely from the hose exit point outside the cab
  

If the hose is damaged or brittle, replace it with a high-temperature, flexible drain tube rated for HVAC use. Avoid using fuel line or garden hose substitutes, which may collapse under heat or vibration.
Preventive Measures and Long-Term Solutions

• Install a screen or mesh cap on the hose exit to deter insects
  
• Add a drain pan moisture sensor to alert operators of overflow
  
• Include hose inspection in the 500-hour service checklist
  
• Park machines on a slight incline to encourage gravity drainage
  

Conclusion
Water intrusion from a blocked A/C drain hose on the Caterpillar D6R can compromise cab integrity and operator comfort. By locating the hose at the evaporator base, inspecting for obstructions, and maintaining clear routing, technicians can prevent costly interior damage and ensure reliable HVAC performance. In high-humidity regions or seasonal storage, proactive drainage management is essential to preserving the dozer’s long-term value.