Hi....
Sounds like those 2 days of freezing got you! The likely cause of the drip is one of two parts.
The poppet or the bonnet. You can be safe and purchase them as a set here for between $55 and $65 ... http://www.sprinklerwarehouse.com/SearchResult.aspx?CategoryID=230
We can help you on here to replace this part...very easy.
If you prefer to have someone fix it for you, email me I have tons of business associates in the PHX area.... Good Luck
Sprinkler Solutions, Inc.
Arizona and Colorado
www.sprinklersolutions.net