308 A/C Thermostat Question

From memory, I think it goes to the expansion valve or temp bulb under the bonnet.

 

I think you will find that is less of a wire and more of a tube.

 

It has nothing to do with the cigarette lighter. That's the temperature sensor tube, which goes all the way to the evaporator/expansion valve. On my picture below you see the opposite end. Normally hidden under thick layers of tar tape.
When I work on anything, what requires removal of the center console I am always anxious to break this tube as well. Has someone ever repaired a broken temp sensor tube? Or does this mean replacement of the whole thermostat switch, which is probably NLA?

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Best from Germany
Martin

 

No, the temperature bulb for the thermostat goes into the fins on the evaporator, through a small hole in the housing (at least it does on my '85 QV). The coiled tube clipped to the suction line goes to the TX valve and regulates how much refrigerant is released into the evaporator. Thermostat switches are freely available - you just need to find one that fits the factory knob.

 

I would be interested as well in repair options. If there aren't any, you can purchase an incredibly expensive replacement (notice the surcharge) after FerrariUK/Maranello Concessionaires has opened their shop again. But noone know, when this will happen.
Sorry for having no better information.

Best from Germany
Martin

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Hi Patrick,

maybe my picture is not completely clear or there were some alterations between the carb and QV cars. The tube I showed is definitely the opposite end of the thermostat switch inside the center console. It is not the coiled tube clipped to the suction line I was referring to. It is the -admittedely hard to see- tube end in the center of my red circle.
I had my evaporator out. There's no temperature sensor going into the housing. I remember how much I was confused after reading this prior to my work and then not finding such a thing.

Best
Martin

 

Oh, OK. Maybe mine's not stock, but most car a/c's run the tube into the fins. I seem to recall a Service Bulletin about moving the TX valve sensor bulb, maybe they also changed it then.

 

I heard/read that the sensor tube on the late cars runs into the evaporator's fins. So it was probably stock on the later injected cars. But definitely not on the earlier cars like my late carb car.

Best
Martin

 

On my GT4 it definitely slides in between the fins of the evaporator core through a small grommeted hole in the housing. I assumed it was a thermocouple that provides voltage to the controller based on temperature at the evaporator.


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That's interesting on such an early car. Maybe it's not an early/late car thing, rather than a Euro/US-car thing?

Best from Germany
Martn

 

FWIW my ‘82 308GTSI the t-stat tube is wrapped around the same evap exit tube as in the red circle of post 4. I have wondered why it would not be inserted into the evap fins, but also makes sense that the exit tube is the highest temp.

 

No, it's a gas that simply operates an on/off switch

 

Refrigeration expansion valves have a coiled tube connected to the top of the valve and the other end of the coil has a bulb about the diameter of your little finger, say 2 inch long. The expansion valve has a designed throughput of freon tuned to the system output and the expansion valve opening is controlled by the expansion of the fluid in the bulb. It is not an on/ off switch as such. The bulb is generally strapped to the gas outlet line from the evaporator and covered in insulation. If the gas coming from the evaporator is too cold then the fluid in the bulb sensors this and contracts, this reduces the pressure on the expansion valve diaphragm and reduces the liquid freon flow into the evaporator. If the gas coming out is too warm then it increases the liquid into the evap.
You need the correct gas flow into the evap to get the best results but as the returning gas cools the compressor you cannot have it coming back too warm, if it comes back too cold then you get liquid freon in the compressor which turns the compressor oil into a gas/ oil bubble mix.
Looking at the previous pic pt no 109809 ferrari temp switch- this is exactly like the thermostat in your domestic fridge and at £10 each it might be worth going to your local fridge repair co to see what they have as the ferrari part is silly money

 

I realize the AC compressor is either running or not running but the use of a variable control knob for temperature suggests this controls how long the AC cycles on and off to maintain a given temperature and I assumed the metal rod is part of this control. If not there would have simply been a switch to turn the AC compressor on and off right?


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The thermostat would control the compressor clutch to start and stop the refrigerant flow. Once the cool temp has been achieved the thermostat tells the clutch to disengage and the compressor stops pumping. The gas in the system would equalize the pressures so the suction and discharge pressures would be the same. The thermostat will have a variable air gap internally to give you a temperature range. Once the thermostat travels the range of the air gap it operates to start or stop the compressor. The switch to start stop the AC is the main system switch.

 

Yes. I was referring to the temp control knob in the centre console.

 

This may be another option. The reviews include a Daytona owner that successfully replaced his rotary AC control.


https://www.summitracing.com/parts/vta-11092-vut?seid=srese1&gclid=CjwKCAjwvZv0BRA8EiwAD9T2VZvP2aJBG9KzTZIfjtSKpBD6UcCsZdlPEwVCWHaKn-uiAt7z2D6ncBoCil8QAvD_BwE



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I am still not clear on the purpose of the metal rod that connects the rotary control to the fins of the evaporator core? Can someone educate me on this?


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The metal “rod” is a capillary tube. It is effectively used to sense the temperature of the evaporator. The colder you set the temperature with the rotary control, the longer the compressor will stay engaged bringing the evap temperature down , once the sensor detects that temperature, it disengages the compressor clutch, until the temp exceeds the set value and re engages it again


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Well said sir

 

Regarding length; I admit I don't know. But if all else fails. Since you have to pull the t-stat tube anyway for replacement, you could pull it now and simply measure the length and add the piece to your measurement which is still on the t-stat switch?
This is, how I would proceed.

Best from Germany
Martin

 

I think the 48" is plenty long enough.

One other observation about adjusting the rotary switch. If you don't set it so that the compressor cycles off occasionally, your evaporator can ice over. Especially during a highway drive.