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'79 308 heater blower motor speeds

Discussion in 'Technical Q&A' started by Dandy_Don, Dec 21, 2003.

  1. Dandy_Don

    Dandy_Don Karting

    Dec 8, 2003
    102
    The Woodlands TX
    Full Name:
    Don McCormick
    I spent several hours yesterday researching my issue on the archives to no avail, so here goes.

    Both heater blower motors work and both are still securely mounted in the proper area just forward of the wheels. All equipment (switch, blower motors, fuse ) appear to be original equipment and unmolested. My problem is the following. When I flick the 3 position fan motor switch to the medium-on position both motors run and push about the same volume of air. When I flick it to the high-on position the passenger side blower motor increases in speed and the volume of air increases out of that side's outlets. The drivers side blower motor however slows down and the volume of air greatly decreases. My first thought was that somehow the leads for medium and high had gotten mixed up for the drivers side blower. However, after consulting the owner's manual electrical diagram, it is clear that each blower motor is fed by a single power wire. And, more interestingly, it seems that the motors are fed in series, rather than parallel ie- the passenger blower motor is fed first from the switch and then the drivers side blower is connected to the hot terminal on the passenger side blower motor. It also appears that the switch on the center console contains the only means of changing the speed of the blower motor as there is no external rheostat anywhere in the circuit. So, my thought then to correct the problem is to run an additional line hot wire directly from the center console switch to the driver's side blower motor to avoid the voltage drop and amp draw of the passenger side blower. Of course, this could be the beginnings of a fuse box issue as it has occurrred to me that I just may not be getting enough current to begin with to run both motors through the fuse. I have not, by the way, done the fuse box upgrade that many others have done here. Any thoughts or advice? Don
     
  2. Mike328

    Mike328 F1 Rookie

    Oct 19, 2002
    2,655
    Boulder, CO
    Full Name:
    Mike
    Woah--you have a 3 position fan motor switch for the heater blower motors? Haven't been in the car for a month (carbs off), but it seems that my switch is just on/off for the blower motors... You have a low/high setting?

    --Mike
    1978 308 GTS
     
  3. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,157
    Texas
    Full Name:
    Steve Magnusson
    Agree that you've got an interesting symptom, but if each blower motor has its "+" lead connected to the same wire then they are in parallel (not series) -- can you clarify? Are you able to measure the voltage at the "+" side for each blower at the two speeds? Like a mis-behaving front lamp, it probably wouldn't hurt to check/freshen the grounds as well -- i.e., if the wiring architechture is such that a single wire comes forward to run both blowers then you've got a problem in the forward wiring (either the "+" network or the ground network) rather than something upstream of the single feed wire.

    See:

    http://www.italiancarparts.com/labels_plates/ferrari_labels_plates.htm

    and scroll down a bit to "Fan, Hazard, Wiper Speed & Aerial Switch Plate Set" -- they went from just "on-off" blowers to "off-low-high" blowers circa '79.
     
  4. Dandy_Don

    Dandy_Don Karting

    Dec 8, 2003
    102
    The Woodlands TX
    Full Name:
    Don McCormick
    Mike, yes I have a 3 position switch, off, medium (or low), and high. Must be a '79 upgrade?!

    Steve, a word of clarification on the wiring. I still think it is series as one wire leaves the switch and then heads to the terminal on the passenger blower. From the terminal on the passenger blower another wire then heads to the drivers side blower motor terminal. Both motors have independent grounds. Isn't this series? If it were parallel would I not have two separate wires from the switch- one to each blower motor? If it is truly wired this way as shown in the owners manual then I am guessing on amperage drop when the switch goes to the high position. Maybe just not enough amps are getting to the first motor terminal to run both and since the passenger one is closer electrically it gets all the amps it needs not leaving much enough for the driver's side. I think I will try jumping out the fuse associated with fan motors and see what happens. I will also try the italian car parts link. Too bad for me that you did not run into a similar problem when you had a 308 as I was hoping that you would have the answer right off the bat. I must admit that I am a bit in awe of your Ferrari knowledge and overall helpful attitude. I would be grateful for whatever thoughts that you have. Thanx Don
     
  5. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,157
    Texas
    Full Name:
    Steve Magnusson
    Don,

    Thanks for the kind words -- (maybe unfortunately), I think you'll find cohabitating for an extended period with any F eventually leads to some familiarity ;)

    With regard to the wiring, even though there's only 1 "+" wire coming to the blower motors, there are two (parallel) paths for the current to flow:

    1) from the "+" wire -to- "+" terminal motor 1 -to- motor 1 winding -to- "-" terminal motor 1 -to- ground, and

    2) from the "+" wire -to- "+" terminal motor 1 -to- the "+" terminal motor 2 -to- motor 2 winding -to- "-" terminal motor -to- ground.

    If it was a series connection, the "-" terminal of motor 1 would be connected to the "+ terminal of motor 2 (i.e., only one current path: "+" wire -to- "+" terminal motor 1 -to- motor 1 winding -to- "-" terminal motor 1 -to- "+" terminal motor 2 -to- motor 2 winding -to- "-" terminal motor 2 -to- ground. Phew.)

    You might give the fan blades of the blowers a (power-off) hand spin/feel just to make sure it's not something mechanically wrong first, but if they both feel smooth/reasonable, I think the voltage measurements would give you the best insight into the problem (e.g., measure the "+" terminal voltage of each motor relative to a good chassis ground at each speed -- should be equal V on both for a given speed. Measure the "-" terminal voltage of each motor relative to a good chassis ground at each speed -- shouldn't be more than +0.1~0.2V).
     
  6. Birdman

    Birdman F1 Veteran

    Jun 20, 2003
    6,683
    North shore, MA
    Full Name:
    THE Birdman
    Don,
    This is the first I have heard of a carb 308 with speeds on the ventilation fans. I thought they all just had on and off. Maybe this is the problem....a previous owner upgrade gone astray?

    BTW, 91TR is right, you are describing a parallel circuit.

    Birdman
     
  7. Tennlee

    Tennlee Formula Junior

    Feb 10, 2002
    645
    Great Smoky Mountains
    I also have a 79 308GTS, and it does have a 3 pos vent fan. Hi does make both fans run at the same speed.
     
  8. f355spider

    f355spider F1 World Champ
    Rossa Subscribed Owner

    May 29, 2001
    16,555
    USA
    Full Name:
    Hugh G. Rection
    Birdman, 91TR (steve magnusson) is correct in his post that from somewhere in the 1979 308 production, they instituted a three position fan switch with "O"(off), "I" (low) and "II" (high), or something like that...stayed that way right up to the end of 308 production.
     
  9. Mike328

    Mike328 F1 Rookie

    Oct 19, 2002
    2,655
    Boulder, CO
    Full Name:
    Mike
    Hey guys, bringing back this thread a bit. I've done some research into the heater fan motors, and it the ones originally listed are, according to Ferrari UK / Ferrari Owners' Site, superceded by some part number or another. My inclination is to think that these are the multi-speed capable motors.

    The question is, if new heater fan motors were to be purchased, using the superceded and udpated part, would these work with the existing wiring? Do the three-way heater fan motors have any special wiring that the on/off motors don't have?

    It's also clear that we need a new, updated three-way switch, but this part doesn't seem to be superceded like the heater fans... Part # "60053709" according to the owners site...
     

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