Rick's Free Auto Repair Advice

Passenger side carpet wet

Why is passenger side carpet wet?

When you have an issues where you find the passenger side carpet wet, that water can come from only two places: either the windshield seal is leaking or the condensation drain from the A/C evaporator coil is plugged. A plugged drain is far more common than a leaking windshield.

Why does the condensate drain plug up?

When car makers shifted to R-134a refrigerant they had to make changes to the evaporator coil which meant the fins had to be spaced closer together. That tight spacing kept water in place longer than the older style evaporators. As air passes over these tightly packed coils, bacteria can combine with the water and start to grow mold. That mold can morph into slime that eventually clogs the drain tube. In addition, some car makers have discovered that insects are attracted to this decaying organic matter and enter the drain tube to build nests, further clogging the tube.

What causes water to drain onto the carpet on the passenger side?

Once the drain tube is plugged, condensation continues to build around the evaporator coil to the point where it leaks out of the HVAC housing case and onto the carpet—usually on the passenger side.

Musty smell from vents

The science experiment growing in your HVAC system also emits a locker room type musty smell when you turn on the blower. This is evidence that you have mold/mildew growing on the evaporator coil.

How to fix water leaking on passenger carpet.

Your first step is to unclog the drain tube. That tube is usually located at the bottom of the HVAC heater box on the passenger side near the console. Examine the area with a flashlight and look for a rubber tube attached to the HVAC case. If you have access to a floor jack and jack stands, find the tube under the car near the engine firewall. It’s best to unplug the line from there using a pipe cleaner or wire.

Run the pipe cleaner up through the tube and remove it until the water drains out. Then flush the line with clean water using a turkey baster (discard the turkey baster afterwards). Do NOT introduce strong cleaning solutions into this tube! Specifically, you may be tempted to fill the tube with bleach. DON’T do it. Bleach is highly corrosive and can oxidize the aluminum evaporator coil and fins, destroying it (cost approx. $1,000 to replace).

Once you open the drain line and remove the water, treat the evaporator coil with a special anti-bacterial coating with this product

AC smells musty

Keep insects out of the drain hose

The problem of insects building nests in the drain hose has become such a problem that Toyota has issued a service bulletin T-SB-0033-14 to address the problem.

The Toyota bulletin applies to these vehicles:

2010 – 2014 4Runner, Prius

2013 – 2014 Avalon HV, RAV4 EV

2007 – 2014 Avalon, Camry, Camry HV, FJ Cruiser

2009 – 2014 Corolla, Venza

2008 – 2014 Highlander, Highlander HV

2009 – 2013 Matrix

2012 – 2013 Prius C

2010, 2012 – 2014 Prius PHV

2012 – 2014 Prius V

2006 – 2014 RAV4

2011 – 2014 Sienna

2007 – 2014 Yaris

anti-insect tip for drain tubeThe fix includes a new drain tube and a special tip treated with a pesticide (ARNIX®). The tip inserts into the new drain line and prevents insect from building nest in the tube. Find the new drain tube and tip at your Toyota dealer

©, 2016 Rick Muscoplat



Posted on by Rick Muscoplat

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