Thanks to those who helped. A new timer arrived today and confident that I
understood the circuit I quickly fitted it.

Shock - horror - the compressor wouldn't operate.

I refitted the old timer - manually wound it round - still it wouldn't
operate.

Out with the meter - found the circuit to be open circuit to the motor. What
had I done????


Took the terminal cover off the compressor to see if I could track down the
fault - plugged it in again - and it fired up.

Had I disturbed a connection?


No - I did the job so quick and the motor was so hot that the compressor
stalled when I applied power and then tripped the overheat trip.

Working fine now.