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Thread: Defrost Only - Don't think its O-Rings

  1. #1
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    Defrost Only - Don't think its O-Rings

    The other day I started having the A/C shift to defrost whenever I gave it throttle. Now it's full defrost all the time, I can't get it to adjust to anything else. Reading on here I decided to check the O-rings. The previous owner just got a Dorman reman EATC from Autozone before I bought the car. I still took that apart and found nice shiny orange silicone o-rings. Looks like Dorman rebuilt them correctly.

    Now, I was reading on this forum trying to determine if there is a blend door associated with the defrost thing and I got a little confused as everything I read was about the heat/cool blend door. Since the #1 reason for this tends to be vacuum I decided to try a smoke test. I only found one small leak on the EGR housing (not sure if that would be the cause of the defrost only thing).

    I looked under the dash and found what looks like a white vacuum hose just hanging out not plugged into anything. I have attached a picture of this hose. I doubt this is my issue as it just started happening about a week ago and this hose appears to be taped up.

    Besides tearing into the dash, is there something else I should look into?

    IMG_20210829_112500.jpg

  2. #2
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    That vac hose you found is for the auto release E-brake that 300A's had. The later cars that lacked this feature just had that hose chilling.

    I can't say I know the exact problem, I had an issue with my 03 where it was basically stuck on dash vents only and in order to get air to the feet, I had to select floor then shut all the dash vents. I'd found some rumblings on CVN of people who had the same problem and it was a door in the dash that was stuck (not the blend door which is for temp). You might have a similar issue, just spit balling ideas here.


    2016 Ford Mustang GT PP - Lund nGauge, BMR vertical links

    2004 Mercury Marauder - Eaton M112, Billetflow 3.4, Accufab SBTB + Plenum, T-56 Magnum, 4.10s, Stainless Works LTs, 2.5" Exhaust, Borla Stingers, Ridetech Coilovers + Adj rear shocks, FX-R projectors, Wilwood 13" BNSL6 + FNSL4 BBKs, S55 Gauge Cluster
    440rwhp & 406rwtq Tuned by Adam @ Revolution Automotive
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    (Sold) 2003 Mercury Marauder - Stainless Works LT's, Stainless Works 2.5" Catback, JLT Intake, Mo's Xcal4 Tune
    5377/7839

    2000 BMW M5 - Evolve Intake, Evolve Alpha-N tune, Stoptech ST-40 BBK, UUC SSK, Dinan front STB, Dinan RSB

    1996 Ford Bronco - 4" lift, 35" BFG A/T's, Punisher Valve Body, MH1 Projectors

  3. #3
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    Thanks for the help. I did notice just now that it was blowing floor and defrost when I had the fans on high. Hitting any other option on the EATC, i can hear a noise like something is attempting to happen. I did do an EATC self test and it returned all 8s so it thinks everything is good. The part that gets me is it started only going defrost when I hit the gas, letting off the gas it returned to dash vents. In my logic, this still points to vacuum related. I wonder if one of the lines going to the EATC has a leak in it....

  4. #4
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    Quote Originally Posted by khamilton1 View Post
    Thanks for the help. I did notice just now that it was blowing floor and defrost when I had the fans on high. Hitting any other option on the EATC, i can hear a noise like something is attempting to happen. I did do an EATC self test and it returned all 8s so it thinks everything is good. The part that gets me is it started only going defrost when I hit the gas, letting off the gas it returned to dash vents. In my logic, this still points to vacuum related. I wonder if one of the lines going to the EATC has a leak in it....
    Sounds like your problem is certainly vacuum related still. I'd get a mityvac and test each line, I would imagine you could just pull the vacuum plug out of the eatc and test each individually from there.


    2016 Ford Mustang GT PP - Lund nGauge, BMR vertical links

    2004 Mercury Marauder - Eaton M112, Billetflow 3.4, Accufab SBTB + Plenum, T-56 Magnum, 4.10s, Stainless Works LTs, 2.5" Exhaust, Borla Stingers, Ridetech Coilovers + Adj rear shocks, FX-R projectors, Wilwood 13" BNSL6 + FNSL4 BBKs, S55 Gauge Cluster
    440rwhp & 406rwtq Tuned by Adam @ Revolution Automotive
    2063/3214

    (Sold) 2003 Mercury Marauder - Stainless Works LT's, Stainless Works 2.5" Catback, JLT Intake, Mo's Xcal4 Tune
    5377/7839

    2000 BMW M5 - Evolve Intake, Evolve Alpha-N tune, Stoptech ST-40 BBK, UUC SSK, Dinan front STB, Dinan RSB

    1996 Ford Bronco - 4" lift, 35" BFG A/T's, Punisher Valve Body, MH1 Projectors

  5. #5
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    I know someone told me, and it was the case for me also, but the O-rings can look good but not be. Just saying.
    2003 Mercury Marauder 300B (Daily Driver)
    1988 LTD Crown Victoria S

  6. #6
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    I may just order a set of the 007 o-rings just to make sure. I'll pick up a mityvac today and see if I can test those lines this weekend.

  7. #7
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    I had a similar situation happen to me on my 03 F150 only had defrost. Took it apart replaced the o rings and fixed the issue


    Sent from my iPhone using Tapatalk

    1.1999 P71 stock
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  8. #8
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    Quote Originally Posted by khamilton1 View Post
    The other day I started having the A/C shift to defrost whenever I gave it throttle. Now it's full defrost all the time, I can't get it to adjust to anything else. Reading on here I decided to check the O-rings. The previous owner just got a Dorman reman EATC from Autozone before I bought the car. I still took that apart and found nice shiny orange silicone o-rings. Looks like Dorman rebuilt them correctly.

    Now, I was reading on this forum trying to determine if there is a blend door associated with the defrost thing and I got a little confused as everything I read was about the heat/cool blend door. Since the #1 reason for this tends to be vacuum I decided to try a smoke test. I only found one small leak on the EGR housing (not sure if that would be the cause of the defrost only thing).

    I looked under the dash and found what looks like a white vacuum hose just hanging out not plugged into anything. I have attached a picture of this hose. I doubt this is my issue as it just started happening about a week ago and this hose appears to be taped up.

    Besides tearing into the dash, is there something else I should look into?

    IMG_20210829_112500.jpg
    See here:

    https://www.mercurymarauder.net/foru...-HVAC-PROBLEMS

    BTW...

    I can repair your EATC, included is an upgrade to the button and fan wheel lights to LEDs.

    PM me for details.
    “When you can’t make them see the light, make them feel the heat.”
    Ronald Regan

    "The only way to deal with the Islamic State - these blood thirsty, blood-drunken, terrorists -
    is to kill them, keep on killing them, until you kill the last one, then you kill his pet goat."

    Lt. Colonel Ralph Peters

    “Be polite, be professional, but have a plan to kill everybody you meet.”
    "I come in peace. I didn't bring artillery. But I'm pleading with you, with tears in my eyes, if you **** with me, I'll kill you all"
    General James Mattis




  9. #9
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    Mine had the same condition.
    It was a vacuum hose made of white plastic running along the firewall in the engine compartment that was cracked.
    2003 Marauder 300B,
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    ----- John

  10. #10
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    If you have high boost levels you’ll blow off the white vacuum line under the dash. I had to superglue mine.


    Sent from my iPhone using Tapatalk Pro


    Cobra short block / ProCharger F1-A / Cog drive upgrade / Manley valves / Brian Tooley Racing valve springs / 80# inj. / -8 fuel line / -6 return / Aeromotive 340 pumps and regulator / 2012 GT500 TR6060 six speed / twin disc clutch / Driveshaft Shop GT500 upgraded CV joint shaft / BA5000 blow thru MAF/ 4.10's / Ford Racing 31 spline set up and Girdle / Metco D.S. safety loop / Stainless Works headers, cats, and everything else out back / ClassGlass hood / Bob's hood strut mod / Hurst line lock / Metco control arms / Addco front and rear sway bars / Monroe severe duty shocks all around / Race concepts rotors / Badgeless grille / 35% tint / FBM's interior LED kit and ambient lighting kit / Pioneer FB700 deck / kenwood speaker 4 Ch. / Rockford Fosgate 10" sub and amp / Kicker 6 X 8's all around / back up cam / bluetooth / Pioneer Xm / 704 RWHP 603 RWTQ tuned by Mo's Speedshop.

  11. #11
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    I feel like there should be a one way check valve installed to prevent that, my old BMW 745i which was factory turbocharged had such a thing in order to keep any positive pressure out of the entirely vacuum controlled HVAC system.


    2016 Ford Mustang GT PP - Lund nGauge, BMR vertical links

    2004 Mercury Marauder - Eaton M112, Billetflow 3.4, Accufab SBTB + Plenum, T-56 Magnum, 4.10s, Stainless Works LTs, 2.5" Exhaust, Borla Stingers, Ridetech Coilovers + Adj rear shocks, FX-R projectors, Wilwood 13" BNSL6 + FNSL4 BBKs, S55 Gauge Cluster
    440rwhp & 406rwtq Tuned by Adam @ Revolution Automotive
    2063/3214

    (Sold) 2003 Mercury Marauder - Stainless Works LT's, Stainless Works 2.5" Catback, JLT Intake, Mo's Xcal4 Tune
    5377/7839

    2000 BMW M5 - Evolve Intake, Evolve Alpha-N tune, Stoptech ST-40 BBK, UUC SSK, Dinan front STB, Dinan RSB

    1996 Ford Bronco - 4" lift, 35" BFG A/T's, Punisher Valve Body, MH1 Projectors

  12. #12
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    I think the Dorman unit is built slightly different. The 007 o-rings don't fit. They are quite a bit bigger than the opening it needs to slide into. I've attached a picture of the Dorman o-ring vs the 007 o-rings I got. The 007 o-ring is the blue one. The red Dorman o-ring fit snug. I'm going to hit up a junk yard and just get a replacement Ford unit and hope for the best. I did use the Mityvac and tested vacuum on each line. All of them held vacuum except the black one. I'm pretty sure the black one is the purge or whatever you want to call it, though.

    IMG_20210903_180335.jpg

  13. #13
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    Quote Originally Posted by khamilton1 View Post
    I think the Dorman unit is built slightly different. The 007 o-rings don't fit. They are quite a bit bigger than the opening it needs to slide into. I've attached a picture of the Dorman o-ring vs the 007 o-rings I got. The 007 o-ring is the blue one. The red Dorman o-ring fit snug. I'm going to hit up a junk yard and just get a replacement Ford unit and hope for the best. I did use the Mityvac and tested vacuum on each line. All of them held vacuum except the black one. I'm pretty sure the black one is the purge or whatever you want to call it, though.

    IMG_20210903_180335.jpg
    The blue o-ring is the wrong size.

    The black line is the supply. There is no purge line.

    The one you get from the junk yard one will probably need the same repair.

    I can repair your EATC, included is an upgrade to the button and fan wheel lights to LEDs.

    I have repaired a couple of hundreds of these.

    PM me for details.
    “When you can’t make them see the light, make them feel the heat.”
    Ronald Regan

    "The only way to deal with the Islamic State - these blood thirsty, blood-drunken, terrorists -
    is to kill them, keep on killing them, until you kill the last one, then you kill his pet goat."

    Lt. Colonel Ralph Peters

    “Be polite, be professional, but have a plan to kill everybody you meet.”
    "I come in peace. I didn't bring artillery. But I'm pleading with you, with tears in my eyes, if you **** with me, I'll kill you all"
    General James Mattis




  14. #14
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    PM has been sent!

  15. #15
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    Quote Originally Posted by khamilton1 View Post
    PM has been sent!
    PM replied to!
    “When you can’t make them see the light, make them feel the heat.”
    Ronald Regan

    "The only way to deal with the Islamic State - these blood thirsty, blood-drunken, terrorists -
    is to kill them, keep on killing them, until you kill the last one, then you kill his pet goat."

    Lt. Colonel Ralph Peters

    “Be polite, be professional, but have a plan to kill everybody you meet.”
    "I come in peace. I didn't bring artillery. But I'm pleading with you, with tears in my eyes, if you **** with me, I'll kill you all"
    General James Mattis




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