Air Conditioning - New Install leaking water

Ive read alot but still dont know the answer to this problem!
Just had a new 15 seer 3 1/2 ton American Standard heat Pump on outside, and Air handler in attic. I live in Tampa FL. this was done in may.
I had a friend of the family who owns his own business for 30 yrs. do the install, he cut me a deal at $3850 for the unit, and pay the guys $400 under the table for the side work. Sounded fair since it was nearly the same quality as Trane from what Ive been reading and the estimate was $6000 for the Trane from a diff. company.
It is now july and I noticed under the Air Handler the cieling was turning brown, obviously from a leak, after further investigation, i found it was sweating on the outside of the PVC drain line, and the bottom of the cabinet which is installed horizontally.
I called the company they came out said the drain should have been insulted, the drain was checked and running freely, so they insulted the drain. When they opened the cabinet the entire cabinet was covered in water dripping the insulation on the inside of the doors were completly soaked, and they took it off and let it air dry, told me to just run the fan for a few days to dry out the unit, then they put the doors back on and taped the seams and cracks with electric tape saying that it is sucking humidity from the attic through the cracks.
After one week I went up in the attic to check for leaks and found some dripping, and condensation all along the bottom of the cabinet! There is no drain pan outside the cabinet(dont know that their should be one?)
I am truely frustrated, and have damage in my plaster cieling , with a leak still not fixed. Any suggestions?
Also why did this just start after the unit has been installed for nearly three months. the only maintenance I have done was to swap filters from paper to electrostatic.

We see this alot. Many things can do this. One is a coil that has an oil coating on it, so we wash it down first, then slow down the fan speed. sometimes the condensate get flung off the coil and nevers gets into the pan.
Your duct work is the other half of the installation... have them look again at the duct sizing. Also for a horizontal install, a metal strip should have been installed on the apex of the coil and sealant applied in certain areas I remember reading... Also the trap just outside the unit must be 2" deep if its a negative pan (if the blower is after the coil). Make sure its level too.
Hopefully the pan is not cracked. Read the install instructions and see if they were followed, pertaining to the coil. I remember some coils had to be removed and rotated 90 degrees...they need to relook at the install instructions too to see if they missed something. Check that all duct registers are open, and returns are connected. Check the rotation of the blower too.

First, your system is a good system. I like the 15 SEER AM systems. I don't install them but have nothing but good things to say about them.

Next,
You got to be kidding??! there is no axillary drain pan underneath the air handler in the attic? I don't know anyone who doesn't install axillary drain pans in attic installs. Glad I don't know your friend. Get your buddy to install an axillary drain pan underneath the air handler.

Next how cold do you keep your house? Below 74 I am guessing??
Ask your buddy if the return and supply duct is the right size, under sizing can lead to lack of air flow.

for your condensate pipe it needs to be insulated I normally insulate with thick walled tubing insulation.

Another tip is to wrap the Air Handler with Duct Insulation wrap. Like the insulation wrap they wrap water heaters with.
It's like having a cold coke can sit outside on a hot day it's going to condensate unless you put it in one of your beer cooler holders.

next move your thermostat up to 74- 75 or higher because this helps the unit not become as cold which will make it condensate like it's doing.

in Tampa FL.

Code there calls for a P trap on the unit with a overflow cut out on it or in the overflow pan. Also like said a pan under the unit . The drain from this pan has to go too the outside and come out over a door ,window or sidewalk. I dont get why the unit sweats up there. Is the duct work right??? Is the blower set for the right speed??I have had unit down there in the attic and they never sweat. To put a heat pump down there dont pay. You run the heat so short that the cost of the heat pump dont pay. Just put in the electric that is there any way. The best bet there is to put on a hot water recovery system on that AC. That can give you free hot water for about 8 months out of the year and kick up the seer of the AC. Your attic vents good is there enough.

Too add to the great information I would reccomend that you toss the electrostatic filter and use a $5.00 pleated filter. Those electrostatics are restrictive.

Correct me if I'm wrong, but the unit only sweats once it becomes wet INSIDE FROM THE CONDENSATE saturating the insulation thereby making the insulation a conductor of cold condensate water. This starts the sweating. Also if the trap is too shallow it wont work. We had one that had one of those preformed traps and it was worthless. The draw from the airhandler pulled the condensate back sucking air through the trap, and the pan overflowed UNLESS the customer had the fan switch in auto. Then once the fan motor stopped the pan would empty. The cure was simple make a 4" deep trap. The senior tech with me looked at it, and knew immediately what to do...I learned this as a young tech and it stuck...The sticker on my air handler states if the improper fan speed is selected, condensate will blow off the coil....take heed.