Hot Air
09-15-2004, 09:49 AM
#1
Drifting
Thread Starter
Hot Air
I have a constant flow of hot air coming through the defogger vents. Doesn't matter if the fan is off/on, vents open/closed. Any ideas what may be my issue? It seems to go away for awhile after I use the A/C on full blast out of the vents. Whatcha'll think?
09-15-2004, 10:02 AM
#2
Deer Slayer
Lifetime Rennlist
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Lifetime Rennlist
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Check for vacuum leaks. Also, the head unit on the HVAC may be shot. Or the valve in the heater hose just foreward of the firewall may be shot.
Mine did this also-- until I turned off the hot water by hard-wiring the valve in front of the firewall closed. Sorting my issue properly is one of my winter projects...
Mine did this also-- until I turned off the hot water by hard-wiring the valve in front of the firewall closed. Sorting my issue properly is one of my winter projects...
09-15-2004, 10:10 AM
#3
Burning Brakes
Join Date: Apr 2002
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Curt,
Check your uotside temperatur sensor for bad connection - This is placed in the vent-tube to the generator in the front left fender
Can also be a more complicatet failure - Then see the shop manual section 87 pages 108 - 114
Regards from Erik in Denmark
Check your uotside temperatur sensor for bad connection - This is placed in the vent-tube to the generator in the front left fender
Can also be a more complicatet failure - Then see the shop manual section 87 pages 108 - 114
Regards from Erik in Denmark
09-15-2004, 08:18 PM
#4
Pro
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I had this same problem and then I found a vacuum leak. Fixed the vacuum leak, fixed the problem. I used Wally's list of checks to find the vacuum leak. The list was incredibly accurate - said the most common leaks to check in order. I found mine in about 20 minutes. Way better idle and more power after the fix too.
09-16-2004, 12:11 AM
#6
Three Wheelin'
It definitely sounds like you're getting hot coolant to the heater core when it shouldn't be there; I'm assuming you're running the A/C temp setting all the way the left, which should fully close the heater control valve (aka hot water valve).
I'd start by checking that it's a) receiving vacuum and b) installed in the right direction.
The HCV is located under the airfilter box, between the engine and firewall on the passenger side. Once you pull the airfilter box (two 10mm bolts), you'll see it connected to the engine via a short, black hose and band clamped in place.
First, disconnect the white vacuum line, then start the engine and put your finger over the line to check for vacuum. If it sucks, good! If not, you'll need to chase the source of the leak. You'll want a copy of Wally P's (928 Specialist) HVAC paper, which I can forward to you if you PM me. (Er, at least I think I can, right Wally?)
Next check the orientation of the valve itself. The actuator arm should be facing the engine, NOT the firewall. Or, if you have the original unit, that would be the black side facing the engine. If you actually look at the black side of the valve, it's stamped "wasserentrit" or somesuch, meaning "water entry."
If the valve is in backwards, it will not properly stop coolant flow, so you'll have to turn it 'round. Even if the vacuum is not working, you'll want to make sure the valve is installed correctly and holding vacuum, so take it out by loosening the band clamps.
Do this when the engine is cold, for ease of handling and minimal coolant loss. Stuff a rag under the valve to catch the bit of coolant that spills out. Once the valve is removed, suck on the connector nipple for the vac line. This should pull the arm in and close the valve. Hold the vac by stopping the nipple with your tongue, and hold for a few seconds, watching to make sure the arm doesn't start moving back out. That would indicate a leaking valve, which would need to be replaced.
Don't worry, they're cheap (under $20) from the "Big 3." There is also a NAPA all metal HCV that's supposed to be more durable, designed for a Ford truck or something. A search of the Forum should turn up the part number. I've not used it, so I can't say any more on that.
In any case, once you get a functioning HCV installed correctly and receiving vacuum, you should not have any hot air in the cabin vents when the temp selector is fully left/max cool, regardless of whether or not your vent flaps are fully functional.
If not, it's something else!
I think!
Let us know how it goes, and good luck for an easy repair!
I'd start by checking that it's a) receiving vacuum and b) installed in the right direction.
The HCV is located under the airfilter box, between the engine and firewall on the passenger side. Once you pull the airfilter box (two 10mm bolts), you'll see it connected to the engine via a short, black hose and band clamped in place.
First, disconnect the white vacuum line, then start the engine and put your finger over the line to check for vacuum. If it sucks, good! If not, you'll need to chase the source of the leak. You'll want a copy of Wally P's (928 Specialist) HVAC paper, which I can forward to you if you PM me. (Er, at least I think I can, right Wally?)
Next check the orientation of the valve itself. The actuator arm should be facing the engine, NOT the firewall. Or, if you have the original unit, that would be the black side facing the engine. If you actually look at the black side of the valve, it's stamped "wasserentrit" or somesuch, meaning "water entry."
If the valve is in backwards, it will not properly stop coolant flow, so you'll have to turn it 'round. Even if the vacuum is not working, you'll want to make sure the valve is installed correctly and holding vacuum, so take it out by loosening the band clamps.
Do this when the engine is cold, for ease of handling and minimal coolant loss. Stuff a rag under the valve to catch the bit of coolant that spills out. Once the valve is removed, suck on the connector nipple for the vac line. This should pull the arm in and close the valve. Hold the vac by stopping the nipple with your tongue, and hold for a few seconds, watching to make sure the arm doesn't start moving back out. That would indicate a leaking valve, which would need to be replaced.
Don't worry, they're cheap (under $20) from the "Big 3." There is also a NAPA all metal HCV that's supposed to be more durable, designed for a Ford truck or something. A search of the Forum should turn up the part number. I've not used it, so I can't say any more on that.
In any case, once you get a functioning HCV installed correctly and receiving vacuum, you should not have any hot air in the cabin vents when the temp selector is fully left/max cool, regardless of whether or not your vent flaps are fully functional.
If not, it's something else!
I think!
Let us know how it goes, and good luck for an easy repair!
