Video: Aprilaire 4788 400 Humidifier Maintenance Kit

Aprilaire 4788 400 Humidifier Maintenance Kit Product Information and Installation Assembly
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Video Home » Aprilaire 4788 400 Humidifier Maintenance Kit

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Length: 5:12

Hi, I’m Jay, and this is the Aprilaire 4788 maintenance kit. It should be replaced every five years. Included in the kit is a box containing two water panels, a scale control insert, water distribution tray, two floats, a feed tube kit, and a strainer screen.

Replacement is easy. Here’s how.
Be sure to turn the power off before performing any maintenance.
Before performing this service, it is necessary to shut off the water. Find the saddle valve, turn it clockwise until it stops.

There’s no top or bottom to the water panel. Simply slide it into the scale control insert, like this. Here’s the distribution tray, this side here with a little loop must be on the same side as the floats. Snap this into position. Now we’re going to take the float cover, install the floats in it, snap it into position. There are two snaps, one on each side. They must be engaged. Again, there’s a little loop here that must face the same side as the floats. This side will now go towards the inside of the humidifier, this side will go towards the furnace or ductwork. The assembly is now ready to be installed inside of your Aprilaire humidifier.

Grab the end of the feed tube with the orifice in it. Slide the brass nut on first, followed by the nylon furl. Be sure to have the furl with the skinny side pointing towards the end. Now it’s ready for assembly onto the solenoid valve. The feed tube material is rather stiff. On some models, it may be necessary to warm it up with a hair dryer in order to bend it. Be careful not to overheat it.

We’re going to use a half-inch wrench to disconnect the feed tube. Now let’s connect the feed tube to the solenoid valve. Insert the feed tube into the solenoid valve until it bottoms out. Slide the furl and the brass nut forward, and hand tighten it. It’s important at this point to keep pressure on the feed tube so it does not back out of the solenoid valve when you tighten it. Now we’re going to tighten it up.

So now we’re going to change the strainer screen. This is the incoming water line, the solenoid valve, and the feed tube. There’s an arrow here indicating which direction the water flows through the solenoid valve. Here’s the tools we’ll need:
- 7/16 inch wrench
- half-inch wrench
- pair of needle-nose pliers
- and a common paper clip.

Now, we’re going to disconnect the water line. Loosen this up, pull the water line out of the way. Now we’re going to take the paper clip and straighten it out. Alright, that’s straight enough. Now we’re going to bend a small hook on one end of it. There we are. The small hook is going to be used to catch the strainer screen. We’re going to slide it in like this to grab the old one. So, we’re going to reach into the valve, grab the old strainer screen, pull it out, and dispose of it.

Now we’re going to take the new strainer screen, insert it into the solenoid valve, take the straight end of the paper clip and use it to push the strainer screen into place. Now all we have to do is reconnect the water line, tighten it up, and there we have it. It’s all done. Now the only thing we need to do is turn the water back on.

Now we’ll attach the feed tube. It’s a friction fit.

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