getting hotter than oustide air from vent

Mr.~G · Jul 15, 2009

I get outside air from the vents that is 10 deg. warmer that ambient air. All systems seem to be OK. I heard that this can be because the heater box always get some heat from hose and that is just the way they are built - yuch! If so, I wan to find some kind of bypass valve arrangement that I can switch on in the summer. Has any one come across this and found a solution?

79dan · Jul 15, 2009

Mine does the same. It's impossible to drive like that, so I just turn the AC on.

Mr.~G · Jul 15, 2009

True! we can do that, but then there goes the HP and Gas mileage.

blubullett · Jul 15, 2009

I never use the vents. If your hot roll down the windows or turn on the AC It doesn't hurt gas milage that much and if you have to smoke someone flick the ac off.

VEE EIGHT · Jul 16, 2009

Your AC system is located in the engine bay......NEXT TO THE ENGINE.

You do the math.

tag4car · Jul 16, 2009

a/c comp kicks off at wot

Mr.~G · Jul 16, 2009

VEE EIGHT said:
Your AC system is located in the engine bay......NEXT TO THE ENGINE.

You do the math.

It's not about the AC system, it's about the heater core.

bhuff30 · Jul 16, 2009

I don't think the heater has anything to do with it, unless the blend door is getting hung up on something. The blend door controls the amount of air going through the heater and seals reasonably well.
I'd bet the air is hotter just because the temperature of the dash and everything inside is so high. When the car sits with the windows up, everything inside can reach temperatures of 130*+, including the vents, ducts and fans. The outside air you are trying to vent is probably being warmed by this.

streethorse · Jul 16, 2009

This works for me even when its over 100 degrees.....
Run the AC for about 5 or 10mins then switch to vent only.
It cools it off to where it will blow cool air until you park again.

Mr.~G · Jul 17, 2009

I guess that I'm not going to find anyone with a solution other than the obvious.

The technical background on this from Ford engineers is that the heater shut-off valve is located on the after-side of the heater box, which allows hot engine coolant (oxymoron) to infiltrate the heater box and raise its temperature enough to drive up the temperature of the air flowing over it bound for the vents by a few degrees. Design issue? In my mind - yes. Will they fix it - No! What I was looking for was someone that had worked around this problem by inserting some kind of by-pass valve ahead of the heater box, there-by preventing the situation.

Thanks for all the discussion.

bhuff30 · Jul 17, 2009

Say what you want, but there is no practical way to install this kind of bypass. The blend door is actually quite large... about 10"x8" and most of the main ducting behind the dash is 25-30 sq inches. The area behind the dash is very tight already and there is no way you are going to install a bypass with 25 sq inches to move the volume of air needed from the blower to the distribution blocks. I know this because I've removed the dash from several different fox body cars and even have the whole blower/heater/condensor/distributution stuff in the basement.
If this 1-2* difference bothers you that much, you should probably start saving your pennies for a luxury car instead! But obviously, you can't afford this because you can't even afford to run the AC on low. You are not cut out for owning a mustang.

Mr.~G · Jul 17, 2009

Actually the bypass I was thinking about is in the engine compartment - shunting the collant flow from the heater box. And if being cut out to be a Mustang owner is to put up with inferior engineering, then it's no wonder that the ricers are eating our shorts.
BTW my '92 did not have this issue.

bhuff30 · Jul 17, 2009

I didn't take the time to re-read your origional post, so I forgot you were actually talking about water flow. All you said in the recent post was a bypass around the heater core, but didn't specify which fluid.
You could disconnect the 2 heater hoses from the heater core and connect them directly together using a hose barb. That's the simplest option. I guess you could setup 2 valves, one that connect the 2 hoses together and another to block off water flow into the heater core. That's a bit overly complicated and messy though.. and the valves would have to be rated for at least 250*F.

Mstg05 · Jul 17, 2009

Its not really an engineering design flaw, or inferior design, its just not feasable.

The lincoln LS had a bypass valve that had issues. You wanna talk about design flaw, this is it. If it fails, NOTHING works right in the HVAC system. You should be thanking ford that there is no bypass valve, its just one more thing to go bad. Its what us ford mechanics/technicians (or anyone, really) call over-engineering.

Bypassing the coolant to not flow through the heater core, theoretically speaking does seem like a good idea. Less strain on the a/c system, but like I said, one more component that could fail. If the additional 10* is a problem, duct tape over the vents will solve your issue, or you can seal off the fresh air door.

Mr.~G · Jul 18, 2009

True, but is there a way to do it with a single valve? One that would allow the flow as normal and the other position to divert the flow in another direction? That's what I have been looking for. Thanks.

Mstg05 · Jul 18, 2009

Well, it seems like this is something no one can sway you from. I said it before, and I'll say it again, not a good idea, however, its your ride, its your money.

No, there is no particular valve made for this, unless you re-design your cooling system to work like the LS. But I'd say the easiest way to figure something out, is to draw out the cooling system components on a peice of paper, draw the flow of coolant, then go to home depot with your drawing, and stand in the plumbing section, where all the valves are, and just stare at the valves until you figure something out. I think your looking for something you can just pop in a make it work, there is no such solution, you're going to have to make up your own solution.

_RUSH_ · Aug 25, 2009

Sorry, but you don't have any remotely cool under the hood when the V8 is pumpin' except the low pressure AC line.
Do yourself and everyone around you a favor and don't be a cheap ass! TURN ON THE AC instead of stinkin'!!!

stang_ed · Aug 25, 2009

Much negativity in this thread. What the OP asked for is a heater core bypass when he did not need the heater. Certainly this can be done. There are industrial valves that are solenoid actuated that will easily withstand the temperature and pressure of the coolant. When I was involved with designing valve systems we could mix and match valves and interchangeable solenoids. I do not know if there are appropriate 12 volt DC solenoids that would be appropriate (I was not interested in going on line to see). Technically it would be easy to design a bypass system that would work off one switch. Whether there is appropriate room under the hood for it all to reasonably fit is another question.

stang_ed · Aug 25, 2009

Much negativity in this thread. What the OP asked for is a heater core bypass when he did not need the heater. Certainly this can be done. There are industrial valves that are solenoid actuated that will easily withstand the temperature and pressure of the coolant. When I was involved with designing valve systems we could mix and match valves and interchangeable solenoids. I do not know if there are appropriate 12 volt DC solenoids that would be appropriate (I was not interested in going on line to see). Technically it would be easy to design a bypass system that would work off one switch. Whether there is appropriate room under the hood for it all to reasonably fit is another question.

The issue of long term reliability should be a part of any design of this type. Leakages of the coolant would threaten the integrity of the engine.

Flghtmstr1 · Aug 26, 2009

My friend with a Dakota R/T bypasses his heater core in the summer by using a shorter hose that routes the coolant around the heater core. It seems to work for him.

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