328 A/C System: Can I fix This Myself?

Hi Mr. Staino,

That is the A/C thermostatic control leading into the expansion valve (covered in black tar tape). Basically, it "senses" the temperature in the evaporator core discharge and cycles more refrigerant into the evaporator unit. It's the switch under the blue temperature knob on the console. Wou would thread a new one along the path of the old, and simply ensure the "bulb" is along the expansion valve discharge. I'm not sure for a 328, but on other cars I have had this held in place with a metal clip.

I *think* the metal tube is usally filled with a substance that changes physical state based on temperature (solid-->liquid; ammonia?), and I don't think they are repairable. I seem to recall a few years back someone mentioning it is identical to the units used in upright refrigerated soft-drink machines (!). Here's the archives link:

http://www.ferrarichat.com/forum/showthread.php?t=1429&highlight=328+air+temperature+switch

And here's a good book on A/C system principles and operation:

http://www.themotorbookstore.com/autheatairco.html

Now the blue box is not factory-issue (that I have ever seen); I did a quick google search for "HOFCO" and it appears they manufacture aftermarket alarm units. Could this be what this is?

Best,

Carl

 

Spot on Carl

Make sure when your replace the thermostat remote bulb you insert it in the middle of your evaporator core for the air con to work at its most efficiency Failure to do that will either turn the evap into a block of ice or not even cool the car at all

 

The metal piece you broke? No

Your air con will only work if you bridge out your thermostat wiring, by doing that you will have no contol of your cabin temp and your air con will run at the coldest setting full time and also turn your evaporator into a block of ice and thus not allow air flow to flow through it to cool you.

Sorry if I am the bearer of bad new mate but it is a critical part of an air con system

 

That "wire" is a "capillary tube" with a tiny inner diameter, filled with a refrigerant gas. When the cold temperature at the end of the tube causes the refrigerant to liquify, the variation in the vapor pressure of the refrigerant gas flexes a diaphram inside the thermostat to turn the compressor on or off.

When removing the old capillary tube (the "metal wire"), note whether the end is looped over.

When I was reading the application notes for the GE 3ART5 thermostat that was in my 328, I noticed that GE recommends against mounting the end of the capillary tube vertically, because gravity feed will interfere with the sensing vapor pressure.

(GE Thermostat Information PDF)

Presumably, this app note wasn't available on the Internet when the 328 was designed.

I notice that the replacement part sourced by Ferrari a couple of years ago is not from G.E., but is made in Italy, and doesn't really fit: it doesn't have the rear terminals like the 3ART5R, and the wiring is a tight squeeze, the case is hard against the console side, and the "zero" position doesn't point to the correct spot. (And it comes with a "half moon" shaft, so you can't arbitrarily set the knob where you want it.) But the issues with a vertical capillary tube would be the same. The part I removed from my 328 was a GE 3ART5R. (3ART5RF45)

I was going to order a 3ART54 from a local refrigeration supply house, so I could switch the thermostat "off" and let the fan warm the evaporator to prevent frost-up after shutdown, but the 3ART54 also doesn't come in a rear terminal configuration. Then I got distracted doing an electronic design (just for refresher practice doing op-amp design). (Due to other demands on my time, that project has been on hold for a couple of years, now.)

The aircon will work if you put, say, a 5A blade fuse in place of the thermostat, but then you have to watch the temps coming from your evaporator -- you have to run the aircon in bursts, shutting it down when it gets too cold (which is what the thermostat does automatically).

 

I have no real professionsl practical experience with A/C systems, but have read books on it and was wondering if you wanted couldn't you bypass the (almost useless) internal thermostat switch and just install new Thermostatic expansion valve with a connecting tube that sits in front of the evaporator?

The switch on the console would just be a dummy, but not sure of the value of it anyhow.

Mark

 

Augustine,
You probably figured this out already, but just in case,make sure you put in a new dryer (dont know how long your ac system was in disuse). It is cheap, and well worth it. The silica in the old one is probably saturated by now.

Also, I presume you want to stay with R-12 (the smarter choice for Italian cars of the pre-1995). If not, you better make sure your ac guy will purge out ALL the R12 refrig oil (probably mineral oil for R 12). Some techs take shortcuts here.....

Evacuate for at least 2 hrs, and test for leaks, as R12 is pricey, and you dont want to waste it at 40-60$/lb.

 

No