98 blazer ac won't blow cold

My 98 blazer will not blow cold air when the ac is turned on. The compressor turns on and it has been recharged and filled. Now I have noticed that when the heater is on it will blow hot and then cold and repeat for quite a long time and then eventually stays hot. Any suggestions, thank you.

Auto or manual controls?
First thing.
Make sure it has good engine vacuum to controls.
Does the compresser run all of the time or cycle on and off?
Does the reciever dryer and low side line feel cold all of the time or go from cold to hot?

It has auto controls I believe. The link below is a picture of it. I don't know if the link will work.
http://http://www.monsterautoparts.com/CHEVROLET/s10/_s10_images/15-72667.jpg

-I bought a controls unit and put it in thinking that might be it and it was not.
-When I got it recharged and filled at Jiffy Lube they found this problem and told me the compressor turns on and off and vaccum was good. They couldn't find why it was doing it. The receiver dryer and low side line I do not know about, I will have to have someone look at it and tell me. I do not know much about vehicles engines.
Thank You so far.

The auto matic control system can be tester with a ac/heater capable scanner.
But you will need to find a good repair shop to test it.
Let us know how it goes.
Good Luck

Thank You I will do that and let you know.