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So you recently found out that your gmt800/900 doesn't have a cabin air filter. I know, its a huge shock since every other vehicle has one. In case you have no idea what I'm talking about it's a filter that is between your vents and the outside of your truck to keep dust and debris (and possibly foul odors) from entering the cab. Well it turns out Silverados used to have them...the year before the SSS came out. You can thank your friendly GM engineer for trying to save a couple bucks on production and later repairs for people not changing them out regularly. Luckily, enough people complained and GM made a retrofit kit...or at least offered the parts from previous years into one convenient package. Well fret no more, I will show you all how to do this. I know, I know (in a thick whiny nerd voice) "But there are other forums out there that already show how to do this". Shut up and sit down nerd, I'm going to write this up anyway so you don't have to dig through google looking for the one with pictures or one that makes sense. So first things first, before you order any parts or even decide to tackle this you need to take into consideration a few items: Do you have the tools required: Ratchet with 7mm, 1/4, 7/32 sockets (or equivalent) Dremel or other suitable cutting device, preferably with a 90 degree tool head Box cutter or suitable razor blade device Safety Glasses (safety first) Lots and lots of patience Are you comfortable making irreversible cuts into your trucks HVAC system with a high speed rotary tool? Are you at least slightly mechanically inclined? Are you ready to spend an hour swearing at one stupid screw? And most importantly do you know what parts you need? Thats easy. Go out to your truck and open the passenger door. Climb under the dash and using your 7mm socket tool unbolt the 3 screws holding the HVAC shield that protects everything under there. Looks like this: Before you unbolt those screws though I need to warn you (oh wait did you already do that? Well that will teach you for not reading the forum completely before tackling this job). The third screw is above the hump just behind the center console. It is a GIANT PITA. You can do this all without taking it out, but the shield will poke you and get in your way the whole time, and you may even end up breaking it. That being said, if you take this screw out, you'd better be prepared to spend some time trying to put it back in. I can show you a little trick to make it easier when the time comes. For this part only remove the 2 easy ones because you will need to put it back on until you get your parts. Ok so once said shield is out of the way, you need to determine which type of cover you need (and possibly which style filter). There are three types out there. Earlier years (2003-2004) may look like this (lets refer to as Gen1): Later years (2005-2006) may look like this (refer as Gen2): Or even possibly this (2007 and up - refer as Gen3): For the sake of this install we will use mine as an example. I have a 2006 so I've got the Gen2 picture above. So now that you have seen what style cover you have, you need to go online and place an order for the parts. Keep in mind there are two types of filters, a standard pleated filter to keep out dust and debris, and a carbon filter that will keep out dust, debris, and help filter out foul odors. (These filters need replaced yearly by the way) If you have the Gen1 'L' shaped bracket you will need: Cabin Air Filter Cover: GM# 52494070 2x Standard air filters: GM# 19257782 -or- 2x Carbon air filters: GM# 12489479 (this style uses 2 half filters side by side) If you have either the Gen2 or Gen3 style you will need: Cabin Air Filter Cover & Screw: GM# 22759208 Standard air filter: GM# 22759203 -or- Carbon air filter: GM# 23101674 (these styles use only 1 filter, although you can use 2 half filters as well) -or- Alternatively you can also use this complete Dorman Kit: Cover, Screw, and Standard Filter: 259-200 Cover, Screw, and Carbon Filter: 259-201 (I used this one – it worked perfect, and was $48 off amazon) All 3 styles are relatively similar in installation with minor differences so it is very easy to adapt these instructions to your style. So at this point you have received your parts and are ready to get started. Go back and remove that cover like before. Lay something on the floor to catch debris and plastic shavings. Next unbolt the Blower Motor Resistor. It’s the rectangular thing with two 7/32 screws directly to the right of where the filter(s) go. Looks like this: Either unplug both connectors or if you can’t get the PITA one in the back of the Blower, just unplug the one and tuck the Resistor up behind it. This will give you a little extra room to work. Now comes the fun part. Grab your rotary tool with a cutting wheel on it (a 90 degree tool head will make this a million times easier) and safety glasses and start cutting. This is where things vary a little. The Gen 1 you will be cutting an ‘L’ shape hole. This one will have the tab for the cover on the front and the screw post in the rear. Make it look like this: Gen 3 is really easy, just cut between the grooves. I hear it can be done with a razor blade. Gen 2 is somewhat more difficult. You will be cutting a 10.25” x 1” slot. I would recommend you hold the filter up to it so you can see about the dimensions you plan to cut. Just cut slightly smaller than the filter. Cut slow and carefully. This one’s tab is in the rear while the screw post is in the front. Now you don't have to do this with a dremel, but i'll tell you that it will make things easier. This is just a recommendation. You’ll notice that the ‘V’ cuts in the filter are there so you can bend the filter to make it easier to angle into the hole. You can also test fit your cover: Notice the 90 degree head. You won't be able to easily get the dremel in there without it. Alternatively if you want you can purchase the half filters and just cut a hole half the length (the length of one of the half filters). Make sure you bought the Gen2/3 cover though. It will still work with a half cut as it’s meant to sit on the outside of the hole. I prefer to do things right though. Once you get your rough cut look up inside. You will see the factory grooves for the filter that is no longer there (just like how there are screw posts yet no cover). You’ll also likely see years of nasty crap mashed into your heater core. Also take note of the inside dimensions. Just inside your cut you will see the vertical surfaces before it opens up to the heater core. Take your razor blade and very carefully trim your hole so it is even with said vertical surfaces. It will coincidentally be the exact size you need for your filter. Also on the front and back surfaces you will see grooves going vertically all the way to the top. Cut exactly to that center groove sticking out. You should end up with about 2-3mm of surface left all the way around and a flat opening with nothing to catch on the filter. Make sure you make this smooth, as well as the bottom surface where the cover mounts so you get a solid seal. Test fit your filter. It should slide in easily without snagging on burrs, and should stop with the bottom completely flush with the cover surface. Make sure the convenient pull tabs are on the bottom and the ‘V’ cuts are facing to the right. If you used the two half filters you will slide one up and then push it to the back, then slide the second one in beside it. Pull the filter out and use compressed air or something to blow the crap out of the heater core. Put the filter back in. Finally take your new cover and hook the back tab into the slot and set against the filter. Take your new screw and using your 1/4” screw the cover onto the screw post. It won’t take any effort. Don’t use a drill. If you have a Gen2, screw it in until the seal is lightly compressed and the tab should be making contact with the screw post. A Gen 3 will not make contact with the screw post. DO NOT OVERTIGHTEN! Make sure you put your Blower Motor Resistor back in and plug it in. Clean up the area well and grab that HVAC cover. This is the fun part. If you unscrewed only two, good for you, screw it back on. If you unscrewed all 3, take a deep breath. Grab your 7mm, preferably a deep well. Put one of your screws in it and use electrical tape to tape it on, like this: Take the cover and note the PITA screw location. It has a screw well that if you look at the inside has a depression that conveniently will seat right over top of the screw post under the dash. Find said screw post and get your bearings. Take the cover and carefully seat that screw post into the cover’s depression. Now with the other hand take the socket contraption you just made and stick it up in the screw well and try and seat the screw. Once its seated the socket and screw will stay up there while you hand tighten the screw. Once suitably tight put your ratchet on and tighten it. Now pull the socket off. It should come off with the tape. Now tighten the last two screws. You just saved yourself an hour of swearing. Clean up and pat yourself on the back while you breathe in nice filtered air. And don’t forget, the next time you see a GM engineer, punch him in the junk.