Chevrolet Repair: 99 YUKON AC, teflon tape, dye test

Question
I REPLACED THE REAR AC SMALL HIGH PRESSURE LINE CAUSE IT BROKE DUE TO TIRE TREAD FROM A BLOWOUT. USED A FACTORY LINE. SHOULD I HAVE PUT TEFLON TAPE AROUND THE THREADS? ONE GUY TOLD ME I SHOULD. THEN ANOTHER GUY TOLD HE DIDN'T THINK YOU DID ON THOSE TYPE OF COMPRESSION FITTINGS. REASON I ASK IS STILL IS NOT HOLDING FREON. DIDN'T KNOW IF HAVING TEFLON ON THERE WOULD CAUSE THIS TO HAPPEN. I'VE SPRAYED W/ SOAPY WATER TO SEE ANY LEAKS,BUT FOUND NONE. NEXT I MAY RUN A DYE TEST. IS THE UV DYE TEST OR THE DYE TEST WITH THE RED DYE BETTER? SOMEONE SAID THERE WAS A RED OR SOME COLORED DYE THAT YOU COULD SEE BETTER. OR SHOULD I TAKE IT SOME WHERE? THANKS

Answer
HyeSorry for the delay my dad had a bypass surgery on Tuesday and I am just getting to these messages now.

You don't need teflon because of teh oring on the line.  If the oring doesnt stop the refrigerant the teflon sure as hell wont.  Use tracer dy from a parts store. Its usually green or yellow and picked up with a UV light.  Even a UV diode works.  Soapy water works well too for big leaks and really thick soapy water for small ones.  It will look like cream when it comes out.

w