Joe Flanagan Posted October 13, 2011 Report Posted October 13, 2011 There was a short section of duct on the defroster of my 49 Plymouth. Since it was completely rotted away, I decided to replace it but I can't find the exact diameter. I am currently using a piece of dryer duct that I think is 3 inches in diameter. The original duct was less than that but I haven't been able to find anything that size. Even with the fan on high speed the air flow seems weak and I'm wondering if it isn't because of the slightly oversized duct where it enters the diffuser under the windshield. Has anybody found the correct size duct? Quote
chopt50wgn Posted October 13, 2011 Report Posted October 13, 2011 Can't tell you what size it is, but if you are using a corrugated hose that could be why you are seeing less airflow. The corrugation creates turbulence, you need to have a smoother hose. Quote
randroid Posted October 13, 2011 Report Posted October 13, 2011 Joe, When you say duct I'm assuming you mean the hose. I concur with what sunsetdart said about the corrugation creating turbulence, but the correct hoses come in fairly standard diameters and if you can't find the exact size simply get the next size up and seal the ends with duct tape. That's where the "duct" in duct tape comes from, not because it's a good restraint for barnyard fowl. Since the hose will be the same diameter on each end measure the easiest end to get to and you should be home free. Another surprising use for duct tape; that for which it was designed. -Randy Quote
DJ194950 Posted October 13, 2011 Report Posted October 13, 2011 on my 50 it's 2 1/2" id flex heater duct commonly used later for air conditioning. Should be able to buy at auto parts places. I had some left over from the a/c install on my 49 wagon:cool: happy hunting joe doug Quote
Joe Flanagan Posted October 13, 2011 Author Report Posted October 13, 2011 Yeah, I think it is 2 1/2" diameter. What I wound up using was the silver corrugated stuff. I didn't think of the inner surface creating an obstruction. I'll see if I can find the right hose at an auto parts place. Thanks. Quote
Robert Horne Posted October 17, 2011 Report Posted October 17, 2011 Today, I used a shop vac hose for the heater to the defrost vent. On the 38 the defrost vents are very small, problably 1.75 inch. Quote
Plymouthy Adams Posted October 18, 2011 Report Posted October 18, 2011 moving air by forced fan is by desgin turbulence..stock hose was spring ribbed desgin..I believe the input hose to the defront dusct intergral to the body at the pinch weld is approx 2.5 inches..actually just a tad uner but this is OD and is considered 2 1/4 hose..this is available from al of the different after market AC suppliers...odds are you can get this also through a local Auto Air shop..some fresh air ducting form the heat riser on the manifold to the air intake is this size. Quote
Rusty O'Toole Posted October 18, 2011 Report Posted October 18, 2011 The hose doesn't have much to do with it. Cars back then came with corrugated or rough flexible hose and it didn't stop them working. I would look at 2 things, leaks allowing the air to dissipate and the fan itself being clogged up. I have taken old fans out of cars and found the fins filled solid with dust and dirt. Believe it or not this cuts the efficiency of the fan tremendously. You have to take the fan off soak it in soapy water and clean ALL the dirt out of the fins. You can't leave any behind or it will throw the fan out of balance. There may be a little tin thing clipped to the fins, it is a balance weight do not lose it. Clean and sand, then paint with 1 or 2 thin coats of spray paint. Apply it as evenly as you can. Also oil the bearings of the motor with synthetic oil. You will be amazed how well it works. Quote
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