308 A/C Thermostat Question | Page 2 | FerrariChat

308 A/C Thermostat Question

Discussion in '308/328' started by MFlanagan, Apr 2, 2020.

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  1. MFlanagan

    MFlanagan Karting

    Dec 21, 2016
    153

    Martin,
    I was hoping to get the part moving my way while I'm busy getting ready for it. Maybe not the best plan. I'll work on it more next week.
     
  2. MFlanagan

    MFlanagan Karting

    Dec 21, 2016
    153
    I've opened it up and I've gotten the old thermostat and its capillary tube out. Its tube is 81" (a full 2 Meters) long! Some of this length was coiled up under the floorboard. I used a string to check the length necessary and it looks like about 57" (min.) would reach, but would be stretched pretty tight.
    I found a Thermostat on the internet that is about 72" long,
    http://www.partdeal.com/mei-rotary-thermostatic-switch-12-24v-with-72-in-capillary-length-adjustable-1337.html
    It is intended for Tractors and Over the Road Trucks. Some of you know much more about air conditioning systems than I do. Do you see any reason why the above thermostat switch wouldn't work -- or is there a better choice somewhere else?

    Mike Flanagan
     
    Saabguy likes this.
  3. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,828
    Isle of man- uk
    Take the old one to a fridge repair shop and see what they have to suit- capillary length is just to reach the sensing point and you can curl up the excess, try finding one near to its installed length. The fridge repair shop selection may be in a colder range as fridges are usually about 5 degrees or lower but they might be able to point u in the right direction
     
  4. MFlanagan

    MFlanagan Karting

    Dec 21, 2016
    153
    Mike, I'm practicing social isolation.
    This one has a Temperature Range of 34°F - 52°F - 1°C to 11°C - Does that seem like a temperature range that should be appropriate to a car to you?
    Another Mike
     
  5. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,828
    Isle of man- uk
    where is this sensing the temperature, is it the cabin temperature ? In which case i would think 18 to 22C should be in the range or wider. If i set temp on my 430 it is about 20C as the desired temperature. Minus 1 to 11C is going to be freezing and i would not think it would get that low, except in winter. What is the marked range on the old one
    You could put the tube of the old one in water with a thermometer and put a meter over the contacts to find its range, just warm up chilled water to find its range of operation
     
  6. MFlanagan

    MFlanagan Karting

    Dec 21, 2016
    153
    As Martin pictured in post #4 of this thread: https://www.ferrarichat.com/forum/posts/147133476/ - it is pinched tightly to the cold end of the evaporator. When I said "34°F - 52°F - 1°C to 11°C - " ; what I really meant was 34°F to 52°F (1°C to 11°C) - I meant to say: +1C to +11C. Sorry for my confusing you. And with the broken tube of my original, it really isn't possible for me to calibrate the old switch. It's broken.

    Mike Flanagan
     
  7. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,828
    Isle of man- uk
    Right, looking at the pic in the link above i can see the expansion valve with the capillary tube coiled up on top of its diaphragm and the sensor end tucked into the side of the pipe, this will be the outlet pipe of the evaporator i would think. In the red circle i can see what is left of the end of a capillary tube, again sensing the evap outlet pipe. I have not seen this setup before so they are altering the cabin temp by the evap outlet temperature. I will have to do a bit of reading to make sense of this
     
  8. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,828
    Isle of man- uk
    This part has been replaced by 109253. Subject to availability. Cost is £59_83. Calibrated thermostat
     
  9. MFlanagan

    MFlanagan Karting

    Dec 21, 2016
    153
  10. MFlanagan

    MFlanagan Karting

    Dec 21, 2016
    153
    Mike,
    The red circle shows the good terminal end of the capillary tube and shows where it is attached in the system. I broke the other end of the tube, near the switch - control itself. My understanding is that this switch and sensor is intended to keep ice from forming inside the evaporator. Does +1C to +11C seem to be a sensible temperature range at this point in the system?

    Mike Flanagan
     
  11. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,828
    Isle of man- uk
    The expansion valve controls the temperature of the gas leaving the evaporator , the coil on top of it is attached to the diaphragm and you can see the other end buried into the pipe insulation. If the pipe gets too cold the fluid in the bulb contracts and the expansion valve closes in, reducing the gas flow so the pipe warms up. Your thermostat is controlling the compressor cutting in and out using the clutch.
    Any markings on the side of the switch in the cabin
     
  12. MFlanagan

    MFlanagan Karting

    Dec 21, 2016
    153
    Yes Mike,
    One side says "Ranco" and "Slenderstat" with the numbers 6 (6) A 250V.
    The Other says "A50-PO626" and "21-77-3L" and "K (with some sort of mark that includes the letters VDE) then II - Below that is an S in a circle.
    These are numbers that seem to be obsolete as far as I can determine. I've not been able to match them to anything that Ranco is making now.

    Mike Flanagan
    Image Unavailable, Please Login Image Unavailable, Please Login
     
  13. Martin308GTB

    Martin308GTB F1 Rookie

    Jan 22, 2003
    4,212
    Black Forest Germany
    Full Name:
    Martin N.
    I'm not sure, whether you refer to the same thing. I was not talking about the expansion valve when showing my picture. If you look very carefully, you see the end of the t-stat tube in the center of the red circle on my picture from post #4.

    Best from Germany
    Martin
     
  14. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,828
    Isle of man- uk
    I know the make, are they a USA company and do they still trade under own name or taken over ?
     
  15. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,828
    Isle of man- uk
    This is where i am getting confused, am i look at one or two tubes. The tube from the expansion valve goes into the coiled spring or what ever it is ( senses the temp and controls the expansion valve opening)
    I take it the bit of tube in the red circle is the end of the second tube from the thermostat in the cabin to control the cabin temp ? It just an odd place to have it as it is measuring gas temp and not cabin temp.
    Or is the bit in the red circle the end of the tube from the expansion valve
     
  16. Martin308GTB

    Martin308GTB F1 Rookie

    Jan 22, 2003
    4,212
    Black Forest Germany
    Full Name:
    Martin N.
    The tube end in the red circle is the one of the t-stat on the center console inside the cabin.
    It runs inside the black sleeve you also see on the right lower quarter of my picture.
    Wayne (waymar) confirmed in post #13, that it's the same on his 2V-i-car.

    Best from Germany
    Martin
     
  17. MFlanagan

    MFlanagan Karting

    Dec 21, 2016
    153
    And the same as on my car, the OP car. With the console cover removed and the right side floorboard removed, the coil you see in this picture is the "in-between" part. between the control in the cabin on the console, and the end you see in Martin's picture.

    Mike Flanagan Image Unavailable, Please Login
     
  18. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,828
    Isle of man- uk
    It is a very odd setup, i would normally expect to see this sensing the cabin air temp. I found a uk dealer of this make of thermostat and sent the details to see if they have a modern replacement
     
  19. MFlanagan

    MFlanagan Karting

    Dec 21, 2016
    153
    Thank you Mike,
    I'll be very interested in their reply.
    Mike Flanagan
     
  20. johnk...

    johnk... F1 World Champ
    Owner

    Jun 11, 2004
    10,629
    CT
    Full Name:
    John Kreskovsky
    This is how the system could work.

    The expansion valve controls the amount of freon flowing through the evaporator. If the compressor ran continuously the expansion valve would open and close trying to maintain a constant temperature of freon exiting the evaporator. This would be max cooling. When the compressor shuts off the temperature of the freon exiting the evaporator will come to equilibrium with the air passing over the evaporator (i'e' the cabin temperature) as the high side pressure drops. So, the temperature of the freon will rise from some level towards the cabin temp. The thermostat senses the exit temperature of the freon as well. With the compressor off, when the temperature of the freon exiting the evaporator starts to rise towards the cabin temperature the thermostat tells the compressor to come on. The setting of the thermostat tells the system when to turn the compressor on based on the freon exit temperature. By changing the setting to "cooler" it is telling the system to restart the compressor when the freon exit temperature cooler. Thus the compressor runs more providing more continuous cooling.
     
  21. thorn

    thorn F1 Rookie
    Silver Subscribed

    Aug 7, 2012
    3,322
    Tallahassee, FL
    That's because it's job is to protect the a/c system and provide refrigerant in a controlled manner. It's not to measure cabin air temp for comfort.
     
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  22. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,828
    Isle of man- uk
    I will agree with that, it just an odd setup compared to others i have seen
     
  23. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,828
    Isle of man- uk
    The expansion valve is variable and is a control valve for the gas. This is just a weird setup
     
  24. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,828
    Isle of man- uk
    First outfit i tried were no help, do they have a supplier in the US ?
     
  25. johnk...

    johnk... F1 World Champ
    Owner

    Jun 11, 2004
    10,629
    CT
    Full Name:
    John Kreskovsky
    Actually, it was pretty standard for the time. These weren't sophisticated systems. They didn't run based on cabin temperature. The occupants just adjusted the thermostat to be comfortable, like a room AC. Basically the T-stat is just telling the system how cool to run the evaporator. If you want it cooler, run the compressor more to keep the evap exit temp colder.
     

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