Heater Tap on A/C Evaporator Box - Alfa Romeo Bulletin Board & Forums
 
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post #1 of 14 (permalink) Old 05-21-2010, 08:33 AM Thread Starter
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Heater Tap on A/C Evaporator Box

Our very own AC Forum - how cool!

I'm a little confused about the kind of heater taps that were used on the Borletti Air Conditioning Evaporator Boxes (105 GTV 2000). In the picture shown and in the Evaporator Box that I sourced from the US there apprears to be a temperature sensor that extends from the heater core (the front of the box - this is indicated in the picture) and that exits the box near the heater tap. How is this setup supposed to work? Did this sensor somehow connect to the tap? I have a sensor (or what appears to be a sensor) that sits on the front of heater core and exits near the heater tap but that connects to nothing (well mine has been cut off anyways and the specs give nothing away). Note that I am not referring to the sensor that is used for the AC Evaporator thermastat.

Any ideas on what role a temperature sensor would have and how this would work? I notice that no one seems to sell the heater taps for the AC models?

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Ok I managed to find a picture of an AC Heater Tap but I am still at a loss as to how the temperature sensor is supposed to work with the tap. Explanations very much appreciated. Might it have something to do with ensuring that the heater tap cannot open when the temperature of the cores is very low therefore indicating that the compressor is in activation???

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I have also copied in an electrical wiring diagram from an Alfetta and Berlina which would be very similiar to the 105 GTV 2000 (1974) but I'm I would appreciate people's views on it's interpretation in the context of my heater tap question

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post #2 of 14 (permalink) Old 05-22-2010, 06:28 AM
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Jonathon,

Would any of these work for you? They are NOS Alfetta items. Two are perfect and slightly different to your valve/tap, in that the exit is at a right angle - but perhaps you can modify the pipe routing accordingly. The one on the left appears to have the same exit as yours (you just need to unbolt and reverse the plated mount, takes ten seconds), but the copper pipe has sheared off at some point in storage. Might be possible to solder on a new one? If interested, send me an email or PM.

Cheers,

Alex.
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post #3 of 14 (permalink) Old 05-22-2010, 09:35 AM
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I try to figure out what you are talking about. is it the red on the pic? If so is turns off the HCV if it is set on heat and you put on the A/C.

edit: I see now the red conects blue(need new glasses)

This was the same system used on the Alfetta,GTV-6 and I think the Milano. At the shop back then we used to put in a std.HCV
without the dohicky. $20 something vs. $100 something(@ the time). Then all you have to do is make sure you turned off the heat!

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post #4 of 14 (permalink) Old 05-22-2010, 09:46 AM Thread Starter
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So you are saying that this sensor ensures that the heater control value is forced closed whenever the AC is turned on.
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post #5 of 14 (permalink) Old 05-22-2010, 10:08 AM
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Quote:
Originally Posted by jonathonlittle View Post
So you are saying that this sensor ensures that the heater control value is forced closed whenever the AC is turned on.
You got it! If the valve is left open and the sensor gets cold it overrides the manual cable and closes the valve. In theory? well none of us at the shop ever bother to check if it really worked.

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post #6 of 14 (permalink) Old 05-22-2010, 10:18 AM
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Quote:
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Jonathon,

but the copper pipe has sheared off at some point in storage. Might be possible to solder on a new one?



Alex.
Can't do that ! thats like soldering your T/A back together when it breaks in half

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post #7 of 14 (permalink) Old 05-22-2010, 10:59 AM Thread Starter
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Ok, if the valve is left open and the sensor gets cold it overrides the manual cable and closes the heater valve. This makes intuiative sense to me but at what point does the valve close?

This is how I think it may work and this is why a sensor controlled value may be preferred to an ordinary cable controlled heater tap. Note that with the Borletti Air Conditioning Evaporator Boxes (105 GTV 2000) that the heater core and evaporator are contained within the one unit.


The evaporator (cold) core is placed first in the air path, which will have the effect of dehumidifying the air when the AC unit is turned on. The air next passes over the heater core re-warming the now dehumidified air which works to defrost a foggy window. So if the AC thermastat is on low (only slightly cold) and heater tap is open then this should work to produce dehumidified defrosting with the heater control value only completely closing when the air gets very cold, that is, when the AC thermastat is set to very cold. The logic being is that if the AC is set to very cold then the goal is most likely to be to cool down the car and not defrost your window.

What do people think?

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post #8 of 14 (permalink) Old 05-22-2010, 11:16 AM
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As far as I can remember the Def/A/C did not work like cars of later


edit nutz: BUT if you cut off the capillary it would work in the way you said -dry air and heat alas defoster!

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post #9 of 14 (permalink) Old 05-27-2010, 11:22 AM
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I was told that the purpose of the sensor tube was to make fine adjustments to the opening of the HCV based on the temperature selected via the slide lever for the purpose of maintaining a constant temperature in the heater core. IOW, it was a very early attempt at automatic climate control, & it was a feature only added to cars with A/C. However, it did not work very well, which, in addition to the cost, is the reason that it is no longer available.

This was all word of mouth to me. It didn't come from any sort of factory literature; so it may not be entirely accurate.

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post #10 of 14 (permalink) Old 08-05-2010, 12:40 PM
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That's correct. The capillary tube sensed temperature and adjusted heater valve position accordingly. The heater valve assy in my 74 GTV was intact and functioning properly until the plastic inlet to the valve cracked and wasn't repairable. Now have a manual heater control valve...works just as well, albeit "manually".

John
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post #11 of 14 (permalink) Old 08-05-2010, 02:00 PM
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Guys,

I believe you have it completely back to front.

From (fading) memory the capillary tube is there to open the heater valve slightly if the A/C gets too cold (ha ha ha) to prevent it from freezing.

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post #12 of 14 (permalink) Old 08-05-2010, 03:12 PM Thread Starter
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So in other words you're suggesting it works like a heater in a kitchen fridge that is used to prevent the core being freezed into a block of ice which would obviously prevent air travelling through it with the outcome of reducing cooling capacity until a complete defrost is done of the core. I did actually have a heater value with temp sensor that I purchased from Alex (see above) and it wasnt closing when I placed it hot or cold water - I was beginning to think I'd been sold a dud. Maybe it was supposed to be opening and not closing as you suggested. I'll give it a try....

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post #13 of 14 (permalink) Old 08-08-2010, 07:15 PM Thread Starter
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well I tested my tap in both the opened and closed positions and when in each position I submerged the sensor in hot and cold water. This did not prove illuminating as the tap neither opened nor closed, partially or completley, in any one of these four test conditions - so it's a faulty tap. I will say Craig, that the tap snapps closed which would make it very hard for the tap to open once the lever on the tap has clicked into the closed position. So bit of a mystery then, does anyone out there have a tap they could test for us to clarity how the original tap was intended to work.
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post #14 of 14 (permalink) Old 08-27-2010, 03:26 PM
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Quote:
Originally Posted by WA-Alfa View Post
cold water
Try sticking the capillary tube (sensor) in the freezer for a while with the valve closed. It should open just enough to gently blow through.

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