Air Conditioning - condenser contactor problem

Yesterday I replaced my condesing unit with a 2 1/2 ton weather king unit. after I hooked everything up, it ran great, I came home later that day and nothing was working. I checked the tranformer and had no voltage coming out. I then replaced the transformer and immediately the other one blew. I then replaced the transformer again and disconnected the two wires running to the condenser unit, the air handler then started working and didn't blow the transformer, I then disconnected the wires at the contactor and checked the wires going to the condenser for a short, but they checked ok, with my ohm meter I show a short when testing the 2 wires that connect straight to the contactor. I was told that it is rare for new contactor to short out, but it seems like this is the problem. Help.....
Richard

You are reading the resistance of the coil if checking the wires connected to the contactor. When you disconnected the 2 wires running to the condensing unit did you disconnect them at the unit outside or close to the transformer?

first thing is put a inlne fuse in the low voltage wire so you dont burn the transformer the contactor could be bad but as stated it is rare for a new contactor to be shorted it is under warranty

if you have a HP and LP saftey on the condenser section they might be shorting the TR.remove the wires going to each one or isolate them so you have 2 pairs of wires just hanging.take your meter on OHMS and touch each pair of wires per safty should read 0.00 now with one lead on one safty wire go to the copper line should rad 1.0 no action or audible on the meter check all 4 wires to ground..but definitly install an in line fuse at the TR and even going into the condenser within the sealed cabinet.

You are reading the resistance of the coil if checking the wires connected to the contactor. When you disconnected the 2 wires running to the condensing unit did you disconnect them at the unit outside or close to the transformer?

Before installing the last transformer, I disconnected the the wires at the air handler and the condenser to see if the wire had a short ( it didn't), the problem starts at the contacter.

Install the inline fuse as was recommended by mrairflow and lets go from there. Ive never seen a shorted contactor come on a new unit in 29 years experience, but hey, theres a first time for everything. Installing the inline fuse will let you troubleshoot this problem without replacing transformer after transformer. You can get one from any electrical supplier and get extra fuses for it. Install in red wire line coming off the transformer.

As your first post reads, it looks like you ran the air handler with the wires disconnected from the condensing unit. Is this correct?
If so look to see if the wires on the condensing unit or the wires coming to the unit have had the insulation torn anywhere and touching any metal.

Just an update: I replaced the new contactor with another new one, and the unit is running like a top. for some reason, when I have a breakdown, it always seems to be something rare. LOL . Thanks guys for all your help. Richard