msmc,
Which Pella windows did you have installed, vinyl or aluminum clad, and what type of window (double hung, slider, casement)? Some of Pella's vinyl windows have the weep holes in the accessory groove at the bottom of the window. If the installer bent the capping to fit inside the accessory groove, he could have plugged the weep holes. If the installer had plugged the weep holes, the water wouldn't be draining down behind your wall. The water would back up in the frame and pool in the sash pocket. During any type of large rain storm the pooling water would end up over flowing into the house. This would be something very visible to say the least.

I can't believe Lowes would just walk away and tell you they can't find anyone to do it cheaper than your installer. I've installed for Lowes for many years now and never found them to ever walk away from an upset customer. Lowes has established pricing for all their installed products. All the installers are paid the same amount of money to install various products. They don't have any installers who get paid more or less than the other, it's all the same pay across the board.
Has Lowes sent out their Pella Representative or have you called out your local Pella Service Technician? You have a local Pella distributor in Pittsburgh. You can call this number, 800-222-8771, and schedule a technician to come out and look things over. Otherwise your best bet is to contact Lowes corporate office and put the heat on.

I also have a problem believing that lowes would walk away from a problem, they do stand behind their install jobs 100%, and as guy exterior man stated all installers are paid the same.
Also cover the weep holes is a issue, but i can not see that being the reason for the amount of water infiltration that you are stating there is some other major issue going on there. Also for mold to being growing that quickly and you experiencing problems that quickly with the mold. Something tells me there was an issue with mold before the windows were ever installed.

1.) The windows are Pella vinyl double hung.
2.) The weeps are not in the accessory groove. The installer went out of his way to caulk the weeps closed. He actually argued with me and Pella, insisting that this is how they should be installed. He also claimed, as did Lowe's, that all of Lowe's installers are trained by Pella at the Pella factory. Pella confirmed that they DO NOT TRAIN LOWE'S INSTALLERS.
3.) If water is not able to exit through the weep holes, it will pool in the hollow extrusion of the sill. It will eventually find its way into the wall cavity through any small opening in the extrusion.
4.) Lowe's walked away from the problem. They still employ this installer and he continues to caulk weeps. He admits that he has been doing this for years. Lowe's knows this, and they still give him jobs.
5.) I have contacted via telephone and mail; the Lowe's store manager, Lowe's regional manager, Lowe's consumer relations, Lowe's customer service, Lowe's chief counsel, Lowe's CEO, Pella regional distributor, Pella corporate customer relations, Pella CEO. Pella's reaction was that the windows were installed incorrectly. They have been the only ones interested in resolving this problem.
6.) I was told by Lowe's that they could not afford to lose this installer, because he works cheap. I have no idea what they tell one installer about what they pay another installer, but since they have lied to me throughout this ordeal, I assume they lie to installers too.
7.) Mold can grow in DAYS. I have seen new drywall exposed to moisture and under the right conditions of temperature and humidity grow to the point that it is visible in less than one week. There were no "issues" before the windows were installed.
8.) This is what happens when the housing industry is booming, as it was the last few years - there is such a shortage of labor that any putz with a Sears charge card can buy a hammer and call himself a contractor.

When will people learn?

Michael