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A/C vent redirecting air

Tiny
DEDHED1
  • MEMBER
  • 1995 FORD MUSTANG
  • 5.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 248,000 MILES
This is for the car listed above, GT model, convertible.
My A/C blows cold so I know there is no leak. But after about 30 minutes run time, it just stops blowing out the main dash vents.
I can still feel cold air drifting from the defrost vents and a little from below.
If I shut off the A/C for 15 minutes and turn it back on, it's fine.
It seems to me that something is freezing over and when it has a chance to defrost, begins working again.
I took it to a mechanic that couldn't diagnose it when it was working. Can you offer any ideas or suggestions as to what might be happening? Thanks
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Tuesday, July 9th, 2019 AT 1:50 PM

8 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
Welcome to 2CarPros.

When this happens, do you mean the blower motor stops working or the air flow direction changes?

As far as air flow direction, that is controlled by what is called a mode door actuator. The blower motor itself is another story.

Let me know exactly what is happening. Also, here is a link that describes the air flow direction and how to fix it. But I'm not sure if that is the issue.

https://www.2carpros.com/articles/low-or-no-air-flow-from-vents

As far as freezing up, it wouldn't cause the fan to stop blowing or the air flow to change directions.

Let me know.

Joe
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Tuesday, July 9th, 2019 AT 9:08 PM
Tiny
DEDHED1
  • MEMBER
  • 5 POSTS
The blower motor is still working because I still feel air being directed up from the upper defrost vents and some near the feet, although not nearly as strong a flow as it would be from the main front vents. Also, you can hear it shut of when I turn the switch off.
As I said, if I turn the A/C off for 15 minutes and then turn it back on, it works just fine. This is why I believe something is freezing up.
It never does this when I first start the A/C, only when it's been running for about 30 minutes. This has really stumped me. I am in the Boca Raton, Florida area (33434) and would gladly take it to someone you recommend that could positively know how to fix this.
Thanks again for your fast reply and suggestions.
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Wednesday, July 10th, 2019 AT 7:13 AM
Tiny
DEDHED1
  • MEMBER
  • 5 POSTS
My 1995 Pony.
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Wednesday, July 10th, 2019 AT 7:20 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
Great car!

I'm near Pittsburgh, so I have no contacts there. I'm sorry. However, in my mind, I can't see how anything would freeze up and cause the airflow to change directions. I attached a pic below. I wrote AC next to where the evaporator housing is located. That is where the cold air comes from. I can't see where something would cause this by freezing.

Also, I do have some other questions. The system is operated from engine vacuum. Do you ever notice a change when the engine is under a load as far as air flow direction? Also, do you run the AC on recirculate all the time?

In addition, I highlighted a couple other things. The vacuum supply hose and the vacuum tank. If enough vacuum isn't provided because of a leak, that can cause air flow to change. If you are in the middle of two different settings, you will notice a decrease in flow.

I am going to ask the owner of the site for his opinion. He is in CA and sees AC issues a lot more than me. You may see an additional person jump in.

Let me know.

Joe
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Wednesday, July 10th, 2019 AT 8:24 PM
Tiny
DEDHED1
  • MEMBER
  • 5 POSTS
Thanks for your help Joe. Not to beat a dead horse, but let me just reiterate.
When my main vents stop blowing cold air, the air seems to come from, or drift up through the upper defrost vents and down from the floor vents.
However, the volume, or force of the air is not nearly as strong as it is coming from the main front vents. Certainly not strong enough to cool down the car.
And since what air I do feel is definitely cold, I am under the belief that the compressor is still working.
Do you believe it might have something to do with the blower motor?
Could it be intermittent depending on the load placed on it?
I'm not an A/C mechanic but if I found a solution, I would have a local mechanic repair it.
Being in South Florida, that A/C is a must.
I don't think it has anything to do with the problem, but I also want to mention that about two years ago I had a heater core leak and had it bypassed. I didn't think being in S. Fl. It was necessary to have the dash ripped apart and the cost involved.
To be sure, this is one perplexing problem.
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Thursday, July 11th, 2019 AT 7:41 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,256 POSTS
Yep, it sounds like the evaporator is icing up due to low charge. when the low side goes too low the evaporator ices up lets confirm the issue by taking a reading. The low side should be about 45 psi and the high side should be about 250 in your weather. here is a guide:

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

Please run down this guide and report back.
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Thursday, July 11th, 2019 AT 10:36 AM
Tiny
DEDHED1
  • MEMBER
  • 5 POSTS
Thanks so much for your reply Ken. For whatever reason, the link you provided won't open for me. But I will take the car in to have pressures checked. Using the numbers you gave me.
One last question. If the pressure was low, would it still be blowing cold when it is working?
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Thursday, July 11th, 2019 AT 10:46 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
Welcome back, and thanks, Ken for your input. Let us know what you find.

Take care,
Joe
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Thursday, July 11th, 2019 AT 7:20 PM

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