ac problems
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Junior User
Joined: Apr 2004
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ac problems
i have a 99 f350 with ac vent problems. air only comes out thru the defrost vents, nomatter what selection you put it in. i blows cold air but it wont move from the defrost mode. any help would be appriciated especially in this south texas 103 temp. thanks
Hotshot
Joined: Jan 2002
Posts: 17,988
Likes: 207
From: La La Land
You have a vacuum leak, as "defrost" is the federally-mandated default mode for vehicle cabin environmental control systems. When there's a vacuum leak, everything stays in defrost mode.
Though you didn't tell us everything about your truck, I'll assume you have a 4WD, 7.3-liter diesel-powered truck. That's what most on this forum have.
The most-likely place to look is at the vacuum lines that are in the front wheel-wells that control the auto-locking ESOF hub locks. Try replacing those lines with appropriate-sized (3/32") fuel line.
It's a cheap start. We'll go from there.
Pop
Though you didn't tell us everything about your truck, I'll assume you have a 4WD, 7.3-liter diesel-powered truck. That's what most on this forum have.
The most-likely place to look is at the vacuum lines that are in the front wheel-wells that control the auto-locking ESOF hub locks. Try replacing those lines with appropriate-sized (3/32") fuel line.
It's a cheap start. We'll go from there.
Pop
Hotshot
Joined: Jan 2002
Posts: 17,988
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From: La La Land
Correction on hose size:
I replaced each of my wheel-well vacuum hoses with 22-1/2 inches of 3/16" (4.8mm) SAE 30R7 fuel hose each side. Secured the ends with a tie-wrap.
It should last a lot longer than OEM, and it fits perfectly.
Pop
I replaced each of my wheel-well vacuum hoses with 22-1/2 inches of 3/16" (4.8mm) SAE 30R7 fuel hose each side. Secured the ends with a tie-wrap.
It should last a lot longer than OEM, and it fits perfectly.
Pop
Hook it, I'll pull it.
Joined: May 2007
Posts: 15,037
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From: Grand Lake, La.
Pop, I am not sure it is his hubs, because he says it does it all the time. It would only come out the defrost when he turns the switch to 4x4. Might be the pump is not working.
I would turn the key on while standing out of the truck to make sure the vacuum pump is working. It should come on for a little while making vacuum.
I would turn the key on while standing out of the truck to make sure the vacuum pump is working. It should come on for a little while making vacuum.
Senior User
Joined: Mar 2007
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My guess would be the pump isn't working. This happened to a friends 99 4x4 SD and his pump went out. Do as Miller_feed suggested and check your vac. pump. I can hear mine come on in the morning when I turn the switch on.
Good luck and let us know what you find out.
Hal
Good luck and let us know what you find out.
Hal
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Hotshot
Joined: Jan 2002
Posts: 17,988
Likes: 207
From: La La Land
Pop, I am not sure it is his hubs, because he says it does it all the time. It would only come out the defrost when he turns the switch to 4x4. Might be the pump is not working.
I would turn the key on while standing out of the truck to make sure the vacuum pump is working. It should come on for a little while making vacuum.
I would turn the key on while standing out of the truck to make sure the vacuum pump is working. It should come on for a little while making vacuum.
But I'd STILL change those hoses!
Pop
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Hook it, I'll pull it.
Joined: May 2007
Posts: 15,037
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From: Grand Lake, La.
You are correct about the hoses. I changed my vacuum lines a few years ago. Factory lines are crap and rot quick.
Elder User
Joined: May 2005
Posts: 582
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From: Refugio, Texas
Pop, I am not sure it is his hubs, because he says it does it all the time. It would only come out the defrost when he turns the switch to 4x4. Might be the pump is not working.
I would turn the key on while standing out of the truck to make sure the vacuum pump is working. It should come on for a little while making vacuum.
I would turn the key on while standing out of the truck to make sure the vacuum pump is working. It should come on for a little while making vacuum.
Thread Starter
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Junior User
Joined: Apr 2004
Posts: 73
Likes: 1
ac problem
i think it is the pump i have heard come on before but now it does't i think that is the problem, does anyone know where the fuse for it is i will check it tommorrow, also it is blowing cold air and then i blows warm air then i after a while it blows cold again i have a new compressor i need to put in but i was also looking for a picture article on how to put a bypass valve to the heater core so it can cool better thanks guy i really apprrieeeaatteee da heeeelllpppp.
Gone Fishin for Mark
Joined: Nov 2004
Posts: 1,354
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From: West of Houston
https://www.ford-trucks.com/forums/5...ditioning.html
Try this for the cold air. The vacuum issue could be a bad pump, easy to diagnose, or a leak that could be the hub lines or hidden elsewhere.
Try this for the cold air. The vacuum issue could be a bad pump, easy to diagnose, or a leak that could be the hub lines or hidden elsewhere.
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