Temperature gauge goes up when air condition on

My vehicle temperature gauge goes up when I turn on the air conditioner, however it does not overheat, air continues to blows cold, and when the air is turned off the temperature returns to normal. I had a blown head gasket that was repaired but the mechanic took advantage of me. Please any suggestions and or comments greatly appreciated to enable me to research before I pay money that I can not afford for services I don't need. Thank you.

Cynthia