My Air Conditioning unit cools but later stops cooling for 2 hours, then works again. Why?

The unit works fine initially if it has not been turned on for a while. As long as the compressor stays running, it works great. However as soon as it stops because the right temperature is reached, the compressor will not start up again unless it has been idle for 2 hours.
Update: Well I let the AC run for a little bit and now the problem seem to solve itself... I just wonder if it's because since the AC is old, and maybe there was a lock in the gas somewhere that clears itself when it's been run for a little bit. I just installed another AC with similar problem...
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