Parking AC Water Leaking Inside the Cab

• Table of Contents

1. Cause 1 — Blocked condensate drain hose
2. Cause 2 — Incorrect vehicle parking slope
3. Cause 3 — Missing or damaged roof gasket
4. Cause 4 — Frozen evaporator coil
5. Cause 5 — Drain pan crack from freeze damage
6. Prevention checklist for fleet operators

A parking AC dripping condensate water inside the cabin is almost never a refrigerant problem — it is a drainage, slope, gasket or icing problem. This guide walks through the five most common root causes and the field fix for each, applicable to all rooftop and under-bunk Vethy parking AC installations.

Cause 1 — Blocked condensate drain hose

The evaporator drain pan routes condensate via a 12–16 mm hose to an external drip point. Mud, insects or sealant plugs the drain. Disconnect the hose, blow compressed air through, and verify free flow before reconnecting.

Cause 2 — Incorrect vehicle parking slope

All rooftop and under-bunk parking AC units assume the vehicle is parked within ±3° of level. Parking nose-up causes condensate to pool toward the rear of the drain pan and overflow into the cab. Park level or block the drive wheels to correct slope.

Cause 3 — Missing or damaged roof gasket

The factory EPDM gasket between the rooftop unit and the roof skin compresses to ~6 mm. UV degradation or improper torque (over- or under-tightened) creates leak paths. Replace the gasket every 5 years or after any roof rework.

Cause 4 — Frozen evaporator coil

Low refrigerant charge or extended low-fan operation freezes the evaporator coil into a solid ice block. When the unit shuts off, the ice melts and overwhelms the drain pan. Diagnose: switch to high-fan, verify no ice formation in 30 min runtime. Fix the underlying refrigerant or fan-speed issue.

Cause 5 — Drain pan crack from freeze damage

RVs stored in sub-freezing conditions without drain-pan emptying can crack the ABS pan. Inspect with a flashlight; replace the pan kit if any hairline crack is visible.

Prevention checklist for fleet operators

Annual: inspect drain hose, roof gasket and drain pan. Pre-season: blow out drain, verify slope, confirm coil ice-free during test cycle. Email service@vethy.com or call +86-532-87729918 for service manuals, spare-parts catalogues and warranty support within 24 hours.

Frequently asked questions

Is condensate water from parking AC normal?

Yes — outside the cabin. A 24V parking AC produces 0.5–1.5 litres of condensate per hour in humid climates. The water must drain externally; any drip inside the cab is a fault.

Can I plug the drain hose to stop the leak?

No. Plugging the drain causes the condensate pan to overflow into the cab. Always fix the root cause.

Why does my parking AC only leak when driving, not parked?

Highway-speed wind can back-pressure the drain hose if the hose end faces forward. Re-route the hose end to face downward or rearward.

How do I prevent freeze damage during winter storage?

Empty the condensate drain pan, run fan-only for 10 min to dry the evaporator, and cover the rooftop unit. For sub-zero storage, blow compressed air through the drain hose.

Does Vethy supply replacement drain pans?

Yes — drain pan kits, gaskets and drain hose assemblies are stocked at the factory.

How tight should the rooftop mounting bolts be?

Hand-tighten until the gasket compresses to ~6 mm visible thickness. Over-torque cracks the roof skin; under-torque leaves leak paths.