The GMC is not known for good ventilation. Driving down the road when the sun is out and the windows are closed is not a good idea – all that glass makes the coach tend be be a little warm up front. The ventilation setting on the dash heater and air conditioning system does nothing – I don’t know if that was improved in later models or not but the 1976 is not too good.
A couple of years ago I made (copied the design I had seen on other coaches) some air deflectors that mounted just in front of the “toll” windows. They scoop the air that goes between the mirror and the side of the windshield and deflect it into the window along with the occasional wasp or bee. Not only does it sometimes get exciting, it is very noisy – putting a screen over the window to reduce the bug flow makes it even noisier.
I decided to do what others had done before me and put some air ducts through the firewall and draw ventilation air through the grill. I copied a design by Kelvin Dietz (http://www.gmcmhphotos.com/photos/showgallery.php?cat=3409) for modifying some 4-inch aluminum dust collection blast gates so I could control them remotely. I used some standard 4 inch vent covers to cover the holes in the floor (firewall), connected them to the modified blast gates with some 4 inch sheet metal duct material, and ran some 4″ all plastic (didn’t want to use any metal near the battery connections on the passenger side) air conditioning ducting hose to the grill area. I connected the 4 inch plastic tubing to my home made (from truck mud flaps) radiator air deflectors with dust collection fittings.
Here are some photos of the finished job:
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I took the grill out so that I could get to the air deflectors to fasten the dust fittings and cut the openings. If you look closely you can see the two 4-inch openings – one on either side. The one on the left side of the photo is a little higher than the one of the right. In the openings you can see the black dust fitting and the gray plastic hose. |
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Closeup of the passenger side opening. Only two screws needed – sealing around the fitting not essential, just holding it. |
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The driver’s side opening is a little lower than the other side. Again, black fitting and gray hose. |
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This is looking down on the driver’s side air deflector from above and to the right of it. The gray hose comes from the foot pedal area and goes down next to the steering shaft. |
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Again, looking down on the driver’s side air deflector you can see the dust fitting attached to the air deflector and the gray hose clamped to it. |
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This shows the modified blast gate attached to the plastic air vent at the top with metal ducting and below to the gray hose. |
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This shows the nice clean installation on the passenger side – the control cable is just above the vent |
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This is the not-quite-so-clean vent installation under the gas pedal – yes, it did get in the way. I was so worried about interfering with the shift lever on the other side of the fire wall that I forgot to think about the gas pedal travel. I bent the lever a little and it seems to be OK. |
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Another view of the passenger side – easier to see the control cable and the piece of aluminum angle I used for a bracket. |
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