Been risking being thrown in the looney bin by riding up and down the highway with a bee hive smoker in the cab of three different trucks. Trying to solve the problem of good a/c at 50mph but all lost at 70mph. First experimented with a 98 Ranger with 300k miles on it which makes it maybe as loosey goosey as an art decco(41-46) or advanced design truck(47-55.1). It has much better sealing properties but with the a/c on "max" or "recirculate" there is a near neutral pressure in the cab but in the fresh air mode there is a positive pressure of COLD AIR pushing the smoke out of any crack. All the after market a/c units I know of use the recirculating method so outside air flowing across doors and other body panels creates a negative pressure that draws the cold air out of the cab. Our first test platform is a 46 Art Decco that we cranked open the windshield, squeezed pipe insulation foam into the crack and then taped with wide duct tape for a good seal. Then two three inch defroster ducts were fitted to gaps cut in the windshield seal and run down to the two squirrel cage fan inlets on the under dash a/c unit. Short sleeves were panel bonded to the evaporator case around the fan inlets to give a place for the defroster ducts to fasten. An art decco truck is even worse that an AD on losing it's cool (no pun intended) but it's cool speed has been raised from 55mph to over 65mph and I think with a better ducting it will reach 70. All this is caused (I think) by the cab being pressurized to a positive pressure by COLD AIR. The register outlet temp only climbed from 38 to 40 degrees when outside air vs inside air passes over the coils. A surprise is on the 48 AD that BY FAR the biggest air escape is past the bottom of the window and down through the door. You've probably noticed the door drain holes are tiny louvers with the opening to the rear to draw air through the door and boy do they work. Well, if all this hasn't put you to sleep I guess you'll just have to take a pill.
Evan, you know I respect you very much, but I lost it when you said you had a bee hive smoker in the cab. I got this mental picture of you sitting in the cab with a safari hat w/ netting around your face! It doesn't surprise me about the AD cab moving air. After all, it was touted as being the "Cab that breathes"!
Bernoulli Principle the faster you move a gas the cooler it becomes and the pressure drops I think this is what you are getting but to a point of diminishing return once you factor in paracidic drag and all Bill
Good Stuff Here ! As always Evan , your immense knowledge & diagnostic skills impress me . Keep them coming ! -Nate (who hates bees)
I had a double shot o' bourbon and came back and re-read that and I'm still completely oblivious to what Coilover is talkin' about. Probably just as well...I hate to weigh in with my advise on something that I haven't got a clue about. Again. This evening. On this website. I'm going back to find where I left that bottle...
I concluded from Evan's test report that one should never fill the cab of his 48 AD with smoke from a bee smoker, run the A/C on "max" while going 55 - 65 mph without putting some duct tape along the bottom of the door windows or else everything will drain out the tiny louvers in the bottom of the door. Now that's some invaluable info the should be printed out and kept in every glove box... Harold P.S. - Please let me know if I didn't get it.
Language I`m glad, that all you native guys had trouble, to understand, what Evan was talking about. I tried hard and read it up and down a few times, but only picked up a tiny bit of it No need for A/C here most time of the year...imagine that, taping all your doors closed from the outside, then try to get into the AD cab through the side window every time, doesn´t seem practical at all
Just put Ram Air into the A/C Evaporator, that way the increased air loss from the cab at higher speeds will be proportionately replaced by the Ram Air.
I really need Neal, (Brit 50), or someone with real smarts on HVAC to weigh in on air flow and duct size. Soon found that just a bit too much outside air piped through the coils lost very little heat and was just outside temp air being rammed into the cab. Am experimenting with a duct with a butterfly valve or "flapper" to synchronize air flow with cooling. As the speed increases the valve has to be closed further so the air has a chance to cool. I think the best scenario will be having an air flow that will keep the inside cab pressure just SLIGHTLY positive. Rather than costantly adjusting the flapper I think one can just set it once when the desired cruising speed is reached.
