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Mark G.
Dodge Dakota
7/24/2001
01:33:52
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 Subject: Vent temperature is hot
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Message:
Seems like the fresh air coming in without the a/c on is much warmer than outside temperature. Doesn't matter how long the car has been driven, sitting in shade, etc. Just seems hot. Oddly, if I run the air for a minute or two, turn it off, the air coming in is then same as outside temp. This is true if I run the a/c, stop and leave the truck in the sun for awhile. It is still cool when I get back in and drive. Is there a temp sensor for this, or could something be broken?
'01 4.7l qc, sports plus package, auto, 3.55 lsd
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4X4Tony
Dodge Dakota
7/24/2001
08:44:15
|  RE: Vent temperature is hot
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Message:
Nah, you've just got a little physics going on. The air system has a door that either moves the air over the heater core or the A/C core. When you're set on Vent and Cold, the fresh air is running over the A/C coil. Now, if you look under your hood, you'll see the A/C lines run over the engine (to the compressor) and next to the exhaust manifold to the condenser (that black can on the firewall). As these lines - and the fluid inside - get hot, the fluid moves and carries this heat to the A/C coil (quite a bit actually). Suddenly, your "cool" fresh air is hot. The fluid will always seek to be the same temperature throughout the system, so between the fresh air cooling the coil inside (making the air hot) and the coil in front of the radiator, the fluid will keep pumping engine heat.
Read this in Popular Mechanics about 10 years ago...
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Mark G.
Dodge Dakota
7/24/2001
11:44:40
| RE: Vent temperature is hot
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Message:
So, if I understand, "fresh" air without the a/c will always be a bit hotter than outside temp? I see the logic, but don't get why it stays much cooler after I've run the air and then turn it off. Don't really use the a/c that often, but almost have to to stay reasonable comfortable, even if it is cool outside. Windows down helps, but gets loud on the freeway.
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4X4Tony
Dodge Dakota
7/24/2001
12:51:08
| RE: Vent temperature is hot
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Message:
You've done three things by running the A/C for a bit - you've cooled the coil down, you've moved a bunch of chilled freon in front of it and, once you turned the A/C back off, the compressor's backpressure check valve has kicked in to stop the freon from flowing on it's own (until the system reaches a more common temperature and the valve releases) - so the coil stays cool and the fresh air flowing past it stays cool - for a while.
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4X4Tony
Dodge Dakota
7/24/2001
12:52:17
| RE: Vent temperature is hot
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Message:
You've done three things by running the A/C for a bit - you've cooled the coil down, you've moved a bunch of chilled freon in front of it and, once you turned the A/C back off, the compressor's backpressure check valve has kicked in to stop the freon from flowing on it's own (until the system reaches a more common temperature and the valve releases) - so the coil stays cool and the fresh air flowing past it stays cool - for a while.
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Mark G.
Dodge Dakota
7/24/2001
13:27:19
| RE: Vent temperature is hot
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Message:
O.K. Now that answers the whole deal. Does everyone else experience this, or am I just having hot flashes?
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Mark P.
Dodge Dakota
7/24/2001
13:52:08
| RE: Vent temperature is hot
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Message:
I've had the same problem since I picked up the truck. I either just turn the system to Off and roll down the windows or run the AC. The Dakota is the worst vehicle for this problem that I have ever owned.
99 CC 4X4 Sport with 318.
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4X4Tony
Dodge Dakota
7/24/2001
14:50:36
| RE: Vent temperature is hot
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Message:
Amen on that!
I bought some DEI Cool-Tube insulation and wrapped it around the A/C line where it runs right across my headers. I also installed one of their Cold Air Tube kits around my FIPK, and used the "extra" to wrap the A/C "black can". Together, that made a HUGE difference.
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Mark G.
Dodge Dakota
7/24/2001
15:12:20
| RE: Vent temperature is hot
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Message:
Now we're talking. Sounds like some good solutions to the problem. Gee, why didn't Dodge do that? Where do you pick up that cool-tube insulation?
Thanks,
Mark
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4X4Tony
Dodge Dakota
7/24/2001
16:00:21
| RE: Vent temperature is hot
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Message:
I got 'em from Summit.
DEI-010406 is 3' of Cool-Tube
DEI-010405 is 3' of Heat Shroud (like Cool Tubes, but with Velcro strip closure)
DEI-010417 is the Cold Air Tube Wrapper.
This stuff is hard to find in the Summit Online Catalog (can only pull up by the part numbers), but DEI's web site is at:
http://www.designengineering.com/product1.html
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Bob E
Dodge Dakota
JOIN HERE
3/12/2002
03:17:58
| RE: Vent temperature is hot
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Message:
I have the same problem. Think the temp control doesn't close at full cold so hot water always runs through heater core. When I clamp the heater hose closed the vent air is same temp as outside air. A thermometer in the vent shows the temp goes up 10 degress when the fan is turned on. Dealer keeps saying this is a normal situation. Had same problem in a motor home and they changed the temp control valve which fixed it. Hate to run AC on 70 degree day.
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Mark G.
Dodge Dakota
JOIN HERE
3/12/2002
10:58:23
| RE: Vent temperature is hot
IP: Logged
Message:
Bob E.
Nice experiment. Maybe we can put in our own little valve to just shut the water off during the summer. Would there be any harm or risk doing that?
You're right; it kills me running the air when it's gorgeous outside (mid 70's right now).
Mark
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