I had an inquiry recently from one of our Auto Glass University graduates. His question reminded me that there are some common problems that technicians should address when prepping a windshield with a rain sensor.

There are two types of rain sensor mountings. In one type the rain sensor is attached to a pre-applied lens, and the other is where the lens is part of the sensor and the unit uses an optically-clear pad to fill the gap between the lens and the glass surface. These two sensor mountings demand two different cleaning and preparation processes that must be completed properly or the rain sensor will malfunction.

First let’s talk about the easy one, the pre-applied lens. This is easy because the glass comes to us with a lens already applied to the surface so we do not have to worry about pads or mixing compounds. The sensor itself is usually attached to the lens with the help of clips or mounting hardware that is easily released and reattached.

You may think there is little we can screw up here, right? Wrong.

It is possible to disrupt the operation of this sensor by how you clean the glass. Most glass with a pre-applied lens come with protective tape covering the lens. This tape is used to protect the lens from handling mishaps that could damage the lens and cause malfunction. However, be aware of another use for the protective covering; to protect the lens from collecting glass cleaner overspray. If glass cleaner gets on the lens’ surface and air dries, the laser beam that causes the sensor to operate will be disrupted and the sensor will not work. It is impossible to clean the lens after glass cleaner is applied to it due to the rough surface and due to the possibility of scratching it with the cleaning towel. It is best to keep the protective tape on the lens until right before the sensor is reattached after replacement.

The next sensor mounting is the pad-mounted type. This type of sensor has the lens incorporated into the sensor itself. The optically clear pad that you obtain for replacement is used to fill the gap between the glass surface and the lens of the sensor. If there are any bubbles or other debris between the lens surface and the glass surface, the sensor will not operate properly because condensation can occur causing drops of water that will be detected by sensor. This leads to a malfunction. This type of sensor usually has a bracket attached to the glass that allows for proper alignment and clip retention. The inner part of this bracket can be cleaned before mounting and this is recommended.

It is always recommended that you replace the pads on every installation. I know. You have salvaged a pad here and there. I have, too, a few times. But, your luck does not always hold true, does it? If you do not want to have your customer inconvenienced, and you don’t want to pay the cost of going back out to do a remount of the rain sensor, then you will get in the habit of changing the pads on every job. Just do it.

To prep for this sensor mounting, it is important to have the pads and the glass at least at room temperature. This will allow the pads to stick properly to the lens and the glass with little or no bubbles. Lay the pad onto the sensor so air can escape out the sides. This is usually done by laying the pad in a bending fashion side to side.

If you choose to use the two-part liquid material, the material must have a convex shape above the sensors outer ridge and not cover the laser window. It is best to have the sensor on a flat surface when applying the material. Once applied it must also be cured a number of minutes before it is applied to the glass surface. Many technicians will attach the sensor to the glass before it is set in the opening.

So there you have it, prepping the glass for rain sensor mounting. I have but one more thing to add, make sure you pre-inspect the sensor before beginning the installation. If it didn’t work before you began the installation, odds are it won’t work when you’re done either.