Here's a quick tip for those of you with recent Chevrolet models. If you park anywhere near trees sooner or later you'll hear strange noises when you turn on your heater or air conditioning – leaves have made their way into your ventilation system and are stuck in the fan. This makes various noises, none of them good – ticking, buzzing, and sometimes it even sounds like a rattlesnake is inside your dash.
Instead of turning the fan off, on, high speed, low speed, etc. trying to dislodge the offending debris, why not open it up and remove all that junk once and for all? Even if you knock this stuff out of your fan, it just goes further downstream and clogs your heat exchanger. Luckily, the ventilation system ductwork is easily accessible, and you can clean it out with a minimum of effort and mechanical aptitude. Here's how to do it.
Turn the ignition off and open the hood. Loosen the coolant overflow tank – it's a 10 mm head bolt on the front, and two tabs in the back. Put this to one side (over the battery). I put the overflow hose into the opening so it won't siphon my coolant out when I tip the tank. Look behind the tank, on the passenger side of the firewall right below the windshield. Hidden behind the tank is the fan.
The vent fan housing is mostly round, with three screws at the 2, 6 and 10 o'clock positions. One electric plug and three screws is all you need to disconnect to take the fan out and get the debris out of your system. The electrical connection is a two-wire plug with a retaining tab. Pull the tab back with something and unplug this socket. It only goes back together one way, so you don't have to worry about remembering how it comes apart.
The three hex head screws are 11/32 on mine, but if you don't have a fancy 1/4 inch socket set you can fake it with an adjustable wrench or pliers. Just be careful – these screws go into plastic, so excessive force is neither necessary nor desirable. Take these screws out and disconnect the drain tube by pulling it off. The fan motor and squirrel cage fan blades will come right out. They're called squirrel cages because they look like those exercise wheels for hamsters – the vanes are on the circumference of a cylindrical sheet metal thingie.
Once you have it out, look for debris stuck in the vanes. Then look into the hole the fan came out of. The opening right in front of you is where the air enters the fan – you'll see the recirculation flap that introduces air from the van's interior. Outside air comes from above. Remove all leaves and twigs you see here. In the photo, mine's already pretty clean – the thing that looks like debris is a little metal clip that is a balancing weight. Leave these in place.
The real treasure trove of debris, however, is downstream from the fan, in the ductwork going to your left. CAREFULLY reach in and pull out the leaves, sticks, branches, small animals etc. that have gone through your air intake and are now jammed up against the air conditioning heat exchanger. This is a tiny radiator that you'll be able to feel the fins of when you reach into this ductwork. It is expensive, hard to replace, and fairly fragile, so don't poke anything but your hand into the ductwork – you do NOT want to damage this little radiator. If you poke too hard, you'll hear the hiss of Freon escaping, and you will weep bitter tears, knowing that you just financed some mechanic's kid through their next semester of college.
Haul out the buckets of stuff that are piled up at the end of this air passage. I had not cleaned mine out in a few years, so I got about a half gallon of vegetative souvenirs accumulated during my travels around the country – even some redwood needles from my time in Big Sur. If they hadn't been blocking my ventilation system I'd have been happier to see them. I figure my airflow was about 50% obstructed with all the junk piled up against this radiator.
Resist the temptation to try to clean the surface of the radiator with anything but the softest of brushes – I used a toothbrush with the handle broken off. Mulch your flowerbed with the fruits of your labor, reinstall and reconnect your fan, reinstall your coolant tank, and the cleaning of your Chevy RV Ventilation System is done. Easy.