very very low pickup with A/C

while consulting with hyundai service center, they told that there is no compression in one of the cylinder. my car has been crossed 46,000 kms.while driving with A/C. there is no pickup in 2nd gear in speed breakers. if i do so then engine got OFF. bt there is no problem in 1st gear and also my car is going top speed upto 140kms with A/C ON. what can i do nw?