Intermittent Air Conditioning

Our 1999 Volvo V70 has an air conditioning system that works intermittently. We can turn it on, it will blow very cold air for a short period of time, then revert to outside temp. air. If we turn it off and wait 10-20 minutes, then turn it back on, it will work again for a short period of time, then stop again.



The mechanic we took it to said we put a small leak in the refrigerant system in a part that hangs down under the front bumper. He ordered the part, but we have yet to get it installed.



My question is why, after more than a month, does the a/c still work well for a short period of time. It seems to me if the refrigerant has leaked out, it wouldn’t work at all. Any ideas?



Thanks!