The thermostat signal to circuit breaker is OK.
The compressor tries to start but doesn't. So is the fan.
Could the capacitor be bad ?
The compressor terminals have a resistance of 2, 4.5 and 1.5 ohms as seen in a digital ohmmeter ( i.e. after removing the terminals from ckt breaker and capacitor)
Appreciate any ideas to further diagnose the problem.
Thanks in advance

The compressor TRIES to start? What do you mean, you hear it hum for a second or two and then it cuts out? Do you have an amprobe? Check the LRA on the compressor, maybe it's stuck.

Thanks for your reply,
I think the compressor tries to start.. I can hear a hum for a second or two and then seems to cut out. I don't have an amprobe, I do have a DMM to measure volts. What is the LRA that you refer to, how do I check it ?
The other think I noticed was the contacts of the circuit breaker was not closing properly I cleaned it but was not of much help. I can hear the ckt brkr operate when I turn on/off the ac. I therefore pushed the contacts by a screwdriver to get past this problem and check. It is when I push the contacts that I hear a hum at the compressor. I am planning to change the ckt brkr also. Please. Let me know how to proceed. Thanks again, Srini

Sounds like your contactor is doing it's job.
LRA is an acronym for "locked rotor amps" and should be stamped on your compressor. You need an amprobe to check this buy hooking it around a lead wire to the compressor during that small time frame where you hear it trying to start. If the LRA on your compressor is 40 and the amp probe reads real close or higher than that, then kicks off, your compressor is locked up.
There are some last ditch efforts to try and unlock it, which in my travels has not worked successfully, so I would guess your going to have to get the compressor replaced.

Shunned Just wondering? If the LRA is 40, What should the draw be on a normal unit? Ie- how much under 40?

The amp draw at first might be in the 20's but just for an instant at startup. It should go back down to maybe 5 or 6 amps to run, depending on the size.

I replaced the capacitor and the circuit breaker and it works like a charm. May be the circuit breaker was OK, but the contact was not holding up well because the "leaf spring" structure seemed week. I got a used ckt brkr and decided to replace. Thanks for your help