Monday, July 15, 2024 Detailed Auto Topics
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Water leaks into vehicles in several ways. People also discover wet carpeting in their vehicles in many ways. Sometimes stepping on the passenger floor gives a squish. Other times we drop something and find a wet floor when we reach for it. Finding and correcting the source of the problem is imperative to prevent other issues.

The problem with a wet floor

Water in a vehicle is a problem and gets worse quickly

They design automobiles to keep water out of the passenger compartment. Sometimes it finds its way in and the result is always bad. Wet carpeting in an automobile is more than an unsightly annoyance. Wet carpet mildews and mold can form. Moisture also causes stains and will damage the interior with rot.

Excessive moisture leaking into the vehicle interior will also raise humidity in the passenger compartment. This can damage electronic components and cause several electrical problems. Computer failure is common in vehicles with water leaks.

Where the water comes from

Most water leaking into the passenger compartment comes from two broad categories. Environmental water, such as rain, may leak in through flawed sealing systems. This is the topic of next week’s article. This week we explore the more common source of leakage, from the heating and air-conditioning system.

Why is my carpet wet on the right front floor board?

The HVAC system is usually on the right, under the dash

Most of the heating, ventilation and air conditioning or HVAC system in a vehicle, is under the dash on the passenger side. Water on the right front floorboard, under the passenger’s feet, often comes from the HVAC system.

Diagnosis begins with determining the nature of the liquid. A sticky feeling spot, especially if warm to the touch, may suggest engine coolant leaking. A low coolant reservoir sometimes confirms this. Other symptoms may include a sticky film inside the windshield and a sweet odor, like antifreeze in the car. The most likely cause is a leaking heater core.

Fresh water on the floor, with no odor or loss of coolant is more often humidity, removed by the evaporator. Water from humidity, removed by the air conditioner, is normal. They design the evaporator case with a drain. Water seen dripping under the vehicle is from humidity removed by the air conditioner. When the system fails, this water may drip on the carpet and cause problems.

Evaporator water leaking

The evaporator core removes humidity from the passenger compartment. Engineers design the evaporator case to catch this water. A drain allows this water to drip under the vehicle. Dust and debris enter the case with air, drawn in by the blower fan. If the debris plug the evaporator drain, water may back up and overflow into the passenger compartment.

The drain tube must be open and sometimes a nipple helps

A lack of water dripping under the vehicle, with the air conditioner on, is a tipoff of an evaporator case problem. Often, cleaning the drip tube, with compressed air, will restore the drainage. With a more severe problem, we may need to clear the drain several times.

Low pressure compressed air works well and is safe. Never push a wire or any metal object into the drip tube. Evaporator cores are soft aluminum and easily punctured. We may have to remove the dash to replace a damaged evaporator.

Many drip tubes also benefit from a 90-degree nipple, used as an air deflector. Air flowing under the vehicle may push water back into the drain. This normally shows up as a wet floor after hours of highway driving. A 90-degree hose slipped over the end of the drain helps deflect the air and allows the evaporator to drain.

Jeep and Chrysler case leaks

Some Jeep and Chrysler products use an evaporator case that seals against the firewall, inside the vehicle. In time, the seals sometimes deteriorate and water runs between the case and the floor. Repair requires dash removal and resealing the case to the floor. Fortunately, most other vehicles do not use this design.

Confirming the problem

We may confirm an evaporator case leak by first removing the water and drying the carpet. Disable the air conditioner compressor, by removing the fuse or unplugging the clutch. Drive the vehicle on a dry day or let it run under a covered area. If the floor gets wet, the more likely cause is a leaking heater core.

The heater core leaking

A hole from galvanic corrosion

A leaking heater core is always the symptom of another problem. Replacing the core is usually a short-term fix. Most times, galvanic corrosion or system erosion has damaged the core. Continued problems and expensive reworking are the result of a failure to diagnose the cause.

Modern cooling systems are very complex and improper service causes most corrosion. Our Detailed Topics, Antifreeze & Coolant Tips and Replacing Engine Coolant, cover this in detail. Before attempting to replace a leaking heater core, reading and understanding this information is very wise.

An internal restriction reduces heater core erosion.

Excess cooling system flow may also erode the heater core and cause a leak. Ford and other companies design heater hoses with a restriction to slow coolant flow in the heater core. Replacing this hose with a standard hose may cause the heater core to fail repeatedly.

Replacing a heater core may require removing the dash. Doing it once is expensive. If we fail to diagnose the cause, the result is a recurring failure and more expense.

In the next article, the topic is water that enters from external sources.

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