Heat issue with speed and upgraded water pump | FerrariChat

Heat issue with speed and upgraded water pump

Discussion in 'Mondial' started by Aceofspades, Jun 18, 2021.

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  1. Aceofspades

    Aceofspades Karting

    Apr 24, 2019
    62
    Chicago
    Full Name:
    Kevin K
    1990 mondial T
    So my heater control valve fails to say closed at cursing speed forcing me to always have hot air or a heat build in the heater core.
    I rebuild the last valve, But noticed it still has a pulse That opens and closes it even with air vent on And ac.

    Also it seems like hot is bring forced when cruising. Its just a bad seal under pressure ?




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  2. moysiuan

    moysiuan F1 Rookie
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    Nov 1, 2005
    3,628
    Canada
    #2 moysiuan, Jun 18, 2021
    Last edited: Jun 18, 2021
    Since you rebuilt the unit, I presume you put new seals on the original plunger, or put in a new aftermarket plunger. With the heater switch off, this plunger is in its up position, which means no coolant flow/heat. When you press the heater on button, the solenoid forces the plunger down, and you get the coolant flow and related heat. The way the plunger is designed is the flow of coolant is actually supposed to help hold the plunger down, and reduce the power need of the solenoid to hold the plunger in its down position. But this same clever design also causes a side effect problem. If the plunger spring is old, or the crappy chinese made replacement which has a known too weak spring, that spring is what snaps the plunger up when you no longer want heat. ie. heat switch off means solenoid power is off and the plunger is supposed to be pulled into its up position by the spring. But it can't overcome the coolant flow that helps hold it down, especially when the rpms are higher and the water pump is creating more coolant flow in the system, so the plunger gets pushed down and hence you get unwanted heat. So it is not a leaking seal, it is a worn spring.

    The solution is to get an oem plunger, but they are no longer available, only the cheap aftermarket one is (they are now scarce too), even the dealers sell the cheap one (it is also used for Merc and BMW heater valves so some purchase from these vendors).

    If you indeed replaced the whole plunger, you are better off to rebuild your old one, the seal kits are available from eg. Summit Racing. If you rebuilt the original, then its spring is worn and that is not good.

    A bodge that seems to work is you put a thin o ring in the valve body where the rubber diafraghm of the plunger seats. This raises the whole plunger very slightly and allows the coolant flow to not exert quite as much down pressure, allowing the weakened spring to pull and hold the valve up as intended.

    It is worth trying that o ring trick, as the Merc guys seem to have success, indeed it should be done on any rebuild as it seems there would be no downside, and would avoid having to redo things like you are experiencing. Failing that you need to ebay a rare NOS plunger (and many of the Chinese ones are marketed as if they are the OEM ones so buyer beware), or another good used one hoping the spring is not as worn as the one in your own. Superformance lists the new plunger, and charges like it is an OEM item. But it may be the Chinese made part, as that may well be all that is available. I would confirm with Superformance where they are getting theirs from before paying up for it.

    Fyi the original whole Bosch heater valve is the same as used on some of the same period Bentlys, the mount dowel/holes are smaller but you can used the rubber mounts and dowel spacers from your existing one. They are also almost as scarce as the Ferrari one, but there were more of those cars and many are now at the breakers so they do pop up from time to time, often from low milage cars driven in nice climates where the heaters are not on and off as frequently so springs may be ok.
     
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  3. moysiuan

    moysiuan F1 Rookie
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  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
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    30°30'40" N 97°35'41" W (Texas)
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    Were you careful to make sure that the coolant hoses connected to the valve were not swapped? The valve can only seal properly when the coolant's flow direction thru the valve matches the arrow on the valve body. If the hoses get swapped, the pressure overcomes the valve's ability to stay closed, and hot coolant always flows thru the heater unit.
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    Forgot to add that if you measure the voltage between the two wires going to the heater control valve with the engine running (or, maybe with just the key "on"), and are not requesting heat = it should be +12V. That's all the electrical part of the system can do to turn off the heat. +12V there = system trying to hold the heater valve closed.
     
  6. afterburner

    afterburner F1 Rookie
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    Jun 20, 2008
    3,197
    Hong Kong
    1) If there is a pulse and the valve operates that would indicate that there is a control problem, not a valve problem.
    2) The valve is easy to check: disconnect it from its el. supply and power it directly with 12V to close it. If your heater stops (and your hoses are connected correctly - the valve is after the heater core) then you have a control problem.
    3) Take your multimeter to the plug that powers the valve and see if there are pulses or permanent 12V (cold) or 0V (hot).
    4) There is to my knowledge no connection between your fan speed and the operation of the ECU. Unless you press the OFF button, the ecu is under power, the valve operates and even with the fan "switched off" there is minimal power supplied to it. It guarantees minimal air flow through the evaporator to stop icing.
     
  7. Aceofspades

    Aceofspades Karting

    Apr 24, 2019
    62
    Chicago
    Full Name:
    Kevin K
    I was looking to make something very similar as the monovavle just sucks!
     
  8. Aceofspades

    Aceofspades Karting

    Apr 24, 2019
    62
    Chicago
    Full Name:
    Kevin K
    I feel as if there little no room to swap the hoses



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  9. Aceofspades

    Aceofspades Karting

    Apr 24, 2019
    62
    Chicago
    Full Name:
    Kevin K
    I did the testing when I had it apart.
    Off gives me 12 volts! With AC or A/E I get a slow Pulse on the valve.




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  10. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson

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