So I have been trying to get my a/c working and it is a on going battle.  As I try to identify the A/C parts on my 1981 vette, I can't find an expansion valve.  This valve is pictured in the parts books and I do not see one on my car.  If I understand its fuction correctly this valve controls the flow of R-12 or 134a and through this valve I can increase the flow or decrease the flow.

Have you checked the charge level? Rapid cycling can be a sign of a low charge.

I haqve checked the charge level more than three times. Thanks for the suggestion.

Have you checked the pressure on the high and low sides when the compressor cuts out? It could possibly be one of those sensors is going bad.

I was told the pressure numbers were what they should be when it cuts in and out. Where are the sensors located that you are talking about?  Thanks for your help.

When using a gauge set by a certified mechanic, he told me the pressures were where they should be for cutting in and out. Sorry I don't remember the numbers.  When I used a auto zone refill bottle the pressure was in the high green area when it cut in and the low green area when it cut out so I never added any charge.  Thanks for enlighting me about the orfice tube, it has been removed a couple of times and always looks clean.  I have had three different technicians work on this a/c unit and have to date have not been able to get it to work properly for more than 24 hours.  Any suggestions are welcomed.  I have had it dye tested for leaks and there does not appear to be any, I have had it evacuated and refilled three times and it still cycles on and off every 5 seconds.

On the A6 compressor one of them was located on the back of the compressor and I'm not sure where the other one is. But you have an R4 compressor and I don't know where they are. One of the three places you had it to should be able to tell you though.

Thanks, I will find out, appreciate the help.