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HVAC Fuse and Lighting Questions

Discussion in '348/355' started by Loser, Aug 21, 2015.

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  1. Loser

    Loser Formula Junior

    Apr 11, 2008
    791
    Gilroy, CA
    Full Name:
    Tom
    #1 Loser, Aug 21, 2015
    I have a 97 F355 Spider. I am having an issue where whenever I switch the blower to full speed (level 4) it pops the hidden 30A fuse. All other speeds work fine. I have cleaned the contacts for both relays and the fuse (which is not melted). I have also disassembled the HVAC control panel in the center console and cleaned the contacts for the buttons.

    Any ideas where to look next for the cause of blowing the 30A fuse?

    While in the control panel, I measured and verified the resistors. I also managed to break the two bulbs with the stand offs for the buttons. Does anyone have a source/part number for these? I only broke the bulb. The standoff is still intact.

    Thanks,

    Tom
     
  2. hjp

    hjp Formula Junior

    Feb 23, 2013
    591
    Kansas City, Mo.
    Full Name:
    Jerry Peterson
    #2 hjp, Aug 21, 2015
    The only reason a fuse blows is because too much current is flowing through the circuit. The highest speed requires the most current. From what you say, I'd suspect the bearings for the fan motor or the squirrel cage fan. Check to be sure there is nothing inhibiting their motion. If they are a bit hard to turn, you might try lubricating their bearings if they are accessible. It could also be the motor on its way out. If the things I mentioned don't work, you may need to rebuild them or buy new/used replacements.

    The bulbs you need for the 2 push buttons are available from elightbulbs.com. Their part # is EK42390. They are 12V, .72 watt T1 with wire leads base. The "stand offs" you are referring to are insulating covers over the wire leads which must be removed by unsoldering them. Save the insulating covers for reuse. The wire leads on the new bulbs have to be exactly the right length so they don't hit when the button is pushed down but high enough to show properly when in the up position. I made a little jig cut out of a stiff business card to hold the bulbs at the correct height while soldering them in otherwise you need 3 hands. Be sure you tin the leads to make them easier to solder and be sure you suck all the solder out of the circuit board holes.
     
  3. Loser

    Loser Formula Junior

    Apr 11, 2008
    791
    Gilroy, CA
    Full Name:
    Tom
    #3 Loser, Aug 21, 2015
    I'm an electrical engineer, so I'll let the solder techs at work handle the soldering. LOL.
    Thanks for the part numbers. I ordered 4 just to be safe.
    The fan turns freely, but I'll take it apart and see where I might be able to lubricate it. Also, I noticed that the flap seems to be broken causing the actuator to work extra hard to try to close it. I disconnected the actuator and put it permanently on the outside air mode and the fuse is no longer blowing.

    Sent from my SM-G900V using Tapatalk
     
  4. Loser

    Loser Formula Junior

    Apr 11, 2008
    791
    Gilroy, CA
    Full Name:
    Tom
    #4 Loser, Aug 22, 2015
    Well, now the HVAC is always on full blast heat no matter what I set the switches to. Not sure why.

    - Tom
     
  5. m.stojanovic

    m.stojanovic F1 Rookie
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    Dec 22, 2011
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    Miroljub Stojanovic
    #5 m.stojanovic, Aug 22, 2015
    It looks like the culprit was your flap actuator motor that was drawing excessive current (possibly due to internal damage/burning). So, with the fan at full speed, the total current exceeded 30 amps.
     
  6. Loser

    Loser Formula Junior

    Apr 11, 2008
    791
    Gilroy, CA
    Full Name:
    Tom
    #6 Loser, Aug 22, 2015
    Hmmm, maybe, if they are on the same circuit. I'll try unplugging the flap actuator motor and see if that resolves the issues.

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  7. Loser

    Loser Formula Junior

    Apr 11, 2008
    791
    Gilroy, CA
    Full Name:
    Tom
    #7 Loser, Aug 22, 2015
    I've ordered a resettable 30A fuse/breaker. Does anyone know the non-Ferrari part number for the relays? I'd like to replace the two HVAC relays as well.
     
  8. m.stojanovic

    m.stojanovic F1 Rookie
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    Dec 22, 2011
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    Miroljub Stojanovic
    #8 m.stojanovic, Aug 23, 2015
    Last edited by a moderator: Sep 7, 2017
    The two relays are just ordinary standard (normally open) automotive relays with pins 30-87-86-85. Power to all HVAC devices comes from the 30A fuse so anything can cause overload.

    The blower fan speed is controlled electronically by the "power unit" mounted on the left side of the evaporator housing (p/n 63307200). There are two possible reasons for your always full speed: 1. the automatic temperature control (if 355 has one, does it have selection of "manual" and "auto" ?) is confused for some reason causing the fan, via the power unit, to go to full speed; 2. The power unit (the power transistor inside it) has blown/shorted conducting full current to the fan. You can diagnose whether it is 2. if you disconnect the smaller of the two connectors on the power unit - if the fan stops working, the power unit may still be good.
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