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My ventilation fresh air is hot as blazes

S

Slim57

CEG'er
Joined
Jan 3, 2011
Messages
54
Location
Central TX
My ventilation fresh air is hot as blazes, especially after engine/car is warm. Summer came to Texas last week. I think problem is the weather strip between black plastic cowling that mountsbetween hood and windshield, and the car body. Weather strip seems to be age hardened, cracked, partly missing. Weatherstrip is between cowl and car body firewall. The cabin filter mounts beneath cowl, and I think the hardened weather strip is supposed to keep engine radiator air flow that washes over engine from reaching cabin inlet filter.

Above the cowl another weather strip mounts, this one presumably seals cowl to hood. It's perfectly pliable, but perhaps an inch or two short on each end. I figure this one is to keep hot engine air away from input grate at top of cowl.

Has anyone had/fixed this same problem?

Can anyone say if I'm thinking right?

Thanks!
 
Ok, weatherstrip, gluing firewall insulation, sealing cowl to firewall helps, but vent is still a few degrees hotter than ambient. I guess I'll delve into hvac section of service manual next.
Thanks anyway...
 
If its hot out the vent is going to be hot ... you can look at sealing the cowl up but the air is already pulled in from the top. I bet my Focus is even hotter as the cowl area is actually partly over the engine.

I really don't see any issue here. I do not recall anyone bring this up as an issue in the past.
 
Thank you for the information. I do not doubt what you say, but it's hard to figure that vent air should be much more than a degree or two hotter than outdoors, at least when moving: Inlet is at back of hood, hood and firewall are insulated. With car sitting still, idling, I can feel air being drawn in through cowl louvers, and it comes out registers hotter - I'll use thermometer to quantify.

I don't mean to be picky, but where I live hot air is a comfort issue. Sealing cowl already made nice difference, before it wasn't just a little hotter, it was hot. I just traded my daughter for this car, and I'm running issues to ground, this is one of the several.

To clarify, I traded cars with my daughter for this car, I did not trade her for this car!
 
You should probably check the operation of the blend door when it's cool outside and the car hasn't been parked outside in the hot sun. In the vent position, you should be able to cycle smoothly between cool air (almost ambient) to hot if the heater core is warm. With the ignition on, engine off and the ventilation fan off (it needs to be quiet...), you should be able to hear the servo motor changing the position of the blend door as you change the TEMP knob on the dash.
 
Good idea! LN I disconnected the fan to be able to listen to blend door motor. I suspect a problem either with hot/cold setting pot, or blend door servo motor itself: Setting pot has 19 positions, so that it moves in steps, and I think the door should move in 19 corresponding steps. Judging by sound, if all cool is position 1, and all hot is position 19, door only seems to move between positions 16 and 17 - on the hot side of said point, it opens up the heater core, on the cool side of same point it closes HC. With fan reconnected and car running, temperature at registers seems to bear this out.

I think it's easy enough to check pot, voltage at wiper should vary in equal steps between 0 and 12, or 0 and 5.

Does my picture of how blend door should work seem right?
*Also*, while looking under dash, I noticed what looks like a drain on hvac blower housing, with no hose attached! Am I missing a drain hose?

Thanks, everyone!
 
Sounds like you have the blend door function well understood and have the troubleshooting skills and equipment to make a diagnoses, 33 years an an EE and ME myself. The blend door feedback potentiometer is an occasional failure on these cars, usually the blend door motor itself is OK. Never had to replace a blend door assembly on a Coutour, need to have a glance at the shop manual, tho sometimes with Fords it's a marathon dash dismantle for a blend door servo R&R.

Ask me about changing the heater core in my 85 Mustang if you want to hear a tale of woe...

Good luck.
 
No Title

The settings pot doesn't test good, or look good. Infinite resistance across pot, and across wiper to one side, then same from wiper to other until near hot is reached, basically just what I expected. Image is of pot internals, too bad manufacturer chose to go so cheap. Notice broken up thin film, what looks like broken horseshoe should be continuous. It's a wonder it halfway functions.
 

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Happy news! New potentiometer assembly (dashboard temperature control, marked from blue to red) 100% fixed the warm vent air. Nice is the AC will not have to fight same warmness. Much more comfortable. Well worth the $20.00!

New pot measures 7 kilo ohms across the outside, middle terminal varies from 7 kilo ohms down to about 750 ohms, depending on setting.
 
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