Thanks ladyinbliss! We're currently renting and the landlord won't shoulder the cost. But we would be moving out to our own unit within a year so might as well just replace 1 pipe only. We won't be using the other aircon unit anymore coz it's too expensive already and it's only 1 room that we're using at night. The cost to replace one piping is $300+. Prior to this, we incurred about the same cost for the pressure test to find out what's wrong with the aircon.