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Thread: Defrost Stuck On

  1. #1
    SoCAPS Member Muley's Avatar
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    Defrost Stuck On

    I have a 1999 PSD. All of a sudden the air in the cab will only come out of the defrost vents. The switch does not activate anything right now to change the flow. Has anyone had this happen to them? I have not located a fuse for this application yet. I believe this function is controlled with the 2 vacuum lines but not sure where to look to fix at this moment.
    Thanks.
    Muley
    1999.5 F250 PSD 4X4, The Mule
    1/8th ET 8.1 @ 82 MPH
    1/4 13.0 @ 101 MPH
    http://www.mcspadden.cc/themule.html

    1999 F350 DRW, Gold Leader, Homemade Tymar, 4" exhaust, DP Tuned


  2. #2
    SoCAPS Sponsor Diesel Tech's Avatar
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    Quote Originally Posted by muley View Post
    i have a 1999 psd. All of a sudden the air in the cab will only come out of the defrost vents. The switch does not activate anything right now to change the flow. Has anyone had this happen to them? I have not located a fuse for this application yet. I believe this function is controlled with the 2 vacuum lines but not sure where to look to fix at this moment.
    Thanks.
    Muley
    you have a vacuum leak or defective pump.i have seen where something falls down vent causing blend dooor not to move.

  3. #3
    SoCAPS Member fords4life's Avatar
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    Mike, check under the passenger side dash. There is a piece that has 2 or 3 vac lines going into it. Sometimes it gets kicked and knocks one loose.
    RIP Muley 9-25-09
    You're ridin with the best now!


    1999 F-250 XLT Crew Cab Short Box

    4X4 7.3L Powerstroke
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  4. #4
    SoCAPS Member SteveBricks's Avatar
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    With no vacuum it defaults to defrost position. Could be the vacuum pump gave up. Can you hear it when the key is on?
    '06 F250 KR CC SB 4WD

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    Special thanks to Domestic Diesel Shop and Riffraff Diesel Performance
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    9/21/54 - 9/25/09

  5. #5
    SoCAPS Member Muley's Avatar
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    I have inspected the 2 vacuum lines and they look fine but will check again. I am not hearing that sucking sound like in the mule so perhaps the pump is bad. I see it under the hood and will try to test this morning.

    Thanks for the direction guys.
    1999.5 F250 PSD 4X4, The Mule
    1/8th ET 8.1 @ 82 MPH
    1/4 13.0 @ 101 MPH
    http://www.mcspadden.cc/themule.html

    1999 F350 DRW, Gold Leader, Homemade Tymar, 4" exhaust, DP Tuned


  6. #6
    SoCAPS Member Hans-Aka SLick's Avatar
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    Hi I had that happen to my 6.0, I don't know if there's much diff on the 7.3 air system, but if your signals are gone too then it's the VACUUM pump for sure. Pull the little black hose off the Pump plastic part and see if it doesn't suck a little air down into it. If you get nothing, then you have no vacuum to operate the A/C.
    2005 F250 6.0: 4" MBRP stainless cat back, Mag Hytec Tranny & Diff Covers, Banks High Ram intake, IC, Boost tubes, 3.5"Downpipe, SCT X3 custom tune files (Tow,Street,Extreme), EDGE Insight Display, Panasonic DVD, w/ AV+NAV, 300 Watt Inifinity AMP with 6 Sony explodes,Volant Ram air cold intake, 18" Diamo 8k wheels, BfGoodrich tires, Rolltop bed cover, Rancho-9000 adjustable shocks, 2.5" F/End lift. 2WD., Cal Tracs, lovin it....

  7. #7
    SoCAPS Member Hans-Aka SLick's Avatar
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    As a follow up, I am a bit pissed at FORD for this crappy design. We have no vacuum in the intake due to it being turbo charged, So instead of giving us an electrical control for the A/C vents they built a vacuum pump so we end up using the same A/C vent controls as on the Gassers. My thinking is that an electrcial servo type system would be better and last longer and actually be cheaper for FORD to install in the Diesel Pickups, than a complicated vacuum pump system, and they (FORD) then tie this to the signal lamp circuit too! So if the vacuum pump fries for some reason the signal lamps go out too, Amazing.
    2005 F250 6.0: 4" MBRP stainless cat back, Mag Hytec Tranny & Diff Covers, Banks High Ram intake, IC, Boost tubes, 3.5"Downpipe, SCT X3 custom tune files (Tow,Street,Extreme), EDGE Insight Display, Panasonic DVD, w/ AV+NAV, 300 Watt Inifinity AMP with 6 Sony explodes,Volant Ram air cold intake, 18" Diamo 8k wheels, BfGoodrich tires, Rolltop bed cover, Rancho-9000 adjustable shocks, 2.5" F/End lift. 2WD., Cal Tracs, lovin it....

  8. #8
    SoCAPS Member Muley's Avatar
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    Yes Hans I am sure your system would be much better than the one Ford came up with. However...
    It was fuse #28. There was no vacuum on the line behind the glove box. I realized the pump was not coming on with the ignition key. Pulled the connector which was not providing power. Traced it back to fuse 28. That is also the trailer back up lights. I must have popped it when I was rewiring one of my trailers. Happy it was an easy and no cost fix. It was a good exercise.
    Fuse 28.
    Thanks again for the support.
    1999.5 F250 PSD 4X4, The Mule
    1/8th ET 8.1 @ 82 MPH
    1/4 13.0 @ 101 MPH
    http://www.mcspadden.cc/themule.html

    1999 F350 DRW, Gold Leader, Homemade Tymar, 4" exhaust, DP Tuned


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