Alfa Pages

[gritsop]

Hi,

Well, after finding and "rescuing" a complete a/c unit out of a crashed 33 it was high time i had it installed on my Alfa. The process was quite challenging, many obstacles had to overcome, many €€€€ were spent but the result is very pleasing and rewarding.

Last week I had the a/c system charged with R134a freon and everything was successful by reaching around 2.5 C at the vents.

My question to all 33 owners with a/c on their car is the following. Since my evaporator is fitted with a frost sensor and an electronic unit called "thermostat" by the owners manual, I would be pleased if anyone could answer a simple question.

Does the a/c - meaning compressor and radiator fans - stop operation (cycle on , cycle off) when ice starts to form on the pipes? This is supposed to be done as the frost sensor inputs data to the electronic device. The frost sensor when reaching a predetermined value directs the electronic unit to stop operation of the compressor and clutch. This however is not occuring in my situation but the temperature has gone as low as 1.8 C only for some seconds until it reaches 3.0 C where it remains stationary.

I have been advised by my a/c shop that if the thermostat does not give the order to stop a/c operation then it may create huge problem to the compressor. Otherwise a mechanical thermostat should be fitted in order to protect the a/c unit.

Any advise from the experts? How does your a/c unit react when ice forms?

Photos follow of the thermostat



the frost sensor (two grey wires)



and the installation


_________________
Thanassis Gritsopoulos
1991 Alfa 33 1.4 IE
2001 Alfa 147 1.6 Distinctive

http://www.alfa-restoration.co.uk
Parts Shop: www.alfa-restoration.co.uk/shop

[Dr A. 33 1.5IE]

Dear Gristop,

I am not an expert on A/C systems but from my experience on my 33's aircon, the frost sensor what it does is that it only dissengages the A/C compressor clutch when the system reaches freezing temps. Everything else you will hear it working meaning both evaporator fans. When the temp rises again it then the clutch kicks in, the compressor works again and brings cool air in the cabin.

You will feel that when sometimes in traffic, for a couple of seconds if the frost sensor kicks in the air temps drops a bit and the air feels a little humid until the compressor engages again. Also you may notice that when driving and you press the aircon button the compressor drains a little 'go' from the car's performance. If by any chance the frost sensor does the same especially during long drives eg. in the highway, then the fact that the compressor clutch dissengages gives the car a bit more go that you feel it immediatelly and when the clutch engages again you will feel the slight load of the engine. Those moments are when the frost sensor pauses the aircon's function for a few seconds.

The only problem that I see for the aircon's performance is the fact that in our 33s, conditioned air comes only through the central part of the dashboard. The cooling effect would be much better if the side inlets were connected with the main system rather than bringing air straight from the outside.

Anyway enjoy the aircon you installed as the summer gets closer and closer in Greece (although the weather as I 've seen it last week that I was in Athens is still a bit autumn like) and if you need any other help do not hesitate to ask for it.

Take care
_________________
1994 Alfa 33 1.5 IE Cat. 220.000Kms and still going strong!!! (Από την Αθήνα και τώρα στην Λευκωσία)

[Ken McCarthy]

Hi Thanassis

Yes the compressor should cycle off under the frost sensor control. I have not investigated the Alfa system in detail but there are two problems that can occur if this does not happen, both serious.

The first is ice on the evaporator coil. Because of the peculiarity of water, that it expands when it freezes, there are significant forces involved and soft copper coils can be damaged.

Second, the refrigerant may get so cold that it does not fully evaporate. The result is liquid refrigerant returning to the compressor. Liquid does not compress!

I believe when the A/C units ran on R12, the fans on the condenser coils (in front of the front wheels) cycled in sequence to control the condensing phase, ie on cooler days only one fan might work, on hotter days, both. In Australia, these were usually changed to run in parallel when the refrigerant was changed to R134A, to make up for some difference in the performance of the refrigerant. I don't know how this was done in the controls.

Regards
_________________
Ken McCarthy - 16V Sprint

[gritsop]

Hi,

Thank you both for the replies. Actually the suspects on this situation are two. The frost sensor itself and the themostat. Good news is that the electronic elements on the thermostat can be easily replaced. I have already ordered a replacement IC on the thermostat (LM 2903D) in order to begin at a good known basis. If nothing changes then I will go for a new frost sensor.

If possible for any of you: could you measure the resistance of the frost sensor (at normal environment temp and a/c having worked for a while, sensor connector disconnected) and report back the Ohm figures? I would be very interested to have in hand these values to compare mine ...

Ken, the operation of condenser fans depends on the load of the a/c. Compressor clutch and left fan operate together - right side fan operates when the pressure in the trinary valve reaches 15-17 bar and stops when these values are reduced by 3-4 bar.

Regarding convertion of the wiring and simultaneous fan operation is somehow strange since the trinary valve should act on the fans operation. Trinary valve is a kind of switch in the case of malfuction; increase or decrease of pressure which will result in a/c damage.

Anyway thank you again and awaiting for any input.

Regards
_________________
Thanassis Gritsopoulos
1991 Alfa 33 1.4 IE
2001 Alfa 147 1.6 Distinctive

http://www.alfa-restoration.co.uk
Parts Shop: www.alfa-restoration.co.uk/shop

[gritsop]

Hi,

Well ... problem with the thermostat solved. The defective elements were on the thermostat and specifically the IC (LM2903 - voltage comparator) was burned out and one of the two Zener diodes was also blown. Replacing one element at a time did not make any difference until both elements were replaced.



Now the A/C switch reacts like a variable resistor and it can actually trigger the compressor clutch depending on the position of the switch. Both condenser fans operate and the compressor clutch cycles on and off respectively. Ice does not form any more on the low pressure hoses and I now have a fully working A/C unit.

Moreover there was a drop of the performance of the A/C since the first freon charge. The problem was found at the discharge port of the compressor. The charging needle (like the needles of the tyres) was bent and freon was leaking out ... one could actually hear the hisssss by placing his ear close to the port. It was a five minute job for the A/C shop to vaccum freon and replace the needle with a new one. I also had the pipes and unions checked for leaks by the A/C shop and no single leak was found

Looks like the A/C project is over at last and I am waiting for the hot days to arrive in order to check the performance.

Special thanks to Dr.A and Ken for their input

Regards,
_________________
Thanassis Gritsopoulos
1991 Alfa 33 1.4 IE
2001 Alfa 147 1.6 Distinctive

http://www.alfa-restoration.co.uk
Parts Shop: www.alfa-restoration.co.uk/shop

[tvatavuk]

Thanks for that feedback.
I'm in process of buying AC instalation for my P4 so your info will help me better understand AC system.

Cheers
_________________
Tino Vatavuk
Little black dress which replaced Alfa Romeo 33 S 16v Permanent 4 GMo

[gritsop]

Hi Tino,

I 'd be glad to help! Alfa 33 A/C featured four different versions.

Unit on the 16V: features frost sensor
Unit like mine in the photo: with or without frost sensor
Unit fitted under the glovebox with original heater in place

If you have found the last unit then it is not worth dealing with. It is a crap design.

I would advise you to find a unit featuring a frost sensor since it is more effective.

Best regards,
_________________
Thanassis Gritsopoulos
1991 Alfa 33 1.4 IE
2001 Alfa 147 1.6 Distinctive

http://www.alfa-restoration.co.uk
Parts Shop: www.alfa-restoration.co.uk/shop

[tvatavuk]

Hi Thanassis,
Friend of mine had last unit in his 1990 16v and I remember it needed like 5 mins to start cooling car besides that it is in right place for passanger to kick it.

If you have few more pictures of that AC I would appriciate it.
Cheers
_________________
Tino Vatavuk
Little black dress which replaced Alfa Romeo 33 S 16v Permanent 4 GMo

[gritsop]

Hi Tino,

Unfortunately, I don't have pictures from this A/C setup but you may get the idea if you look at the series 3 workshop manual under the air conditioning section.

However if you want pictures of my A/C setup I 'd be happy to share; i ve got loads of them and I am planning to write an article for Bobbber's restoration site.

Regards,
_________________
Thanassis Gritsopoulos
1991 Alfa 33 1.4 IE
2001 Alfa 147 1.6 Distinctive

http://www.alfa-restoration.co.uk
Parts Shop: www.alfa-restoration.co.uk/shop

[tvatavuk]

Hi Thanassis,

I'll take a look at workshopmanual but if you know what are diff between yours and 16v that would help also.
I ment pictures of yours setup. I'm looking forward to article on Bobbers site.

Regards
_________________
Tino Vatavuk
Little black dress which replaced Alfa Romeo 33 S 16v Permanent 4 GMo

[gritsop]

Hi,

Actually the difference between mine and the one off a 16V is basically on the shape and the handling of coolant. As you may know A/C units cut off hot coolant for the heater matrix when A/C is on. In my setup this cutting off is done with the help of a mechanical switch operated via cables. On the 16V version this is done with electrical motors which is far better than the mechanical. Regarding the shape, the 16V version is more round shaped compared to mine as you will see in the pics that follow.

Compressor bracket after wire brushing


Compressor rebuilt:



Evaporator after the rebuilt:


Installation:



Fast Idle Valve:


Freon Charge:


These are some samples from the project. There are loads of pics to describe each section so you will see them at Bobbbers site soon. It was quite a challenging project with many odds to overcome like the wiring harness which was "butchered" and I had to rewire it from the beginning.
In addition I had to buy new condensers since the donor car had a front impact and those didn't survive the accident...

Regards
_________________
Thanassis Gritsopoulos
1991 Alfa 33 1.4 IE
2001 Alfa 147 1.6 Distinctive

http://www.alfa-restoration.co.uk
Parts Shop: www.alfa-restoration.co.uk/shop