My home AC is less than 4 years old (Ruud).
My condensate pan has about 1/2 inch of water int it, the unit is still cooling, and
the condensate line running outside is still dripping water. I can blow thru that line , so it appears to be fairly clear. I poured bleach down it a week ago. Why is my pan still collecting water ?

I assume your talking about the overflow pan under the cooling coil?

If your not, some water laying inside the main drain pan below the coil is common. It could be excessive if the main pan and coil are not level. But not something to worry about.

If you are talking about a overflow pan under the cooling fan/coil unit. There are a few factors that cause the water to collect in the overflow pan.

1. There is no trap on the main drain line leaving the air handler. Without this trap water is drawn back up the pipe while the fan is running and causes the main pan to overflow.
This is the most common cause.

2. Dirty air filter. The fan must pull air through the air handler. It will get it wherever it can. If the filter is dirty the air will be drawn up the drain pipe thus preventing the condensate water from running into the pipe. Check the filter and check the coil for any blockage that may have occured. IN some cases the insulation inside the air handler falls down and partly blocks the coil.

3. Undersized return duct or blocked return ducts. like the dirty filter if air does not come to the fan it creates a lower pressure within the air handler. This causes the air to be drawn up the drain pipe and then overflows.

4. Check the level of the air handler and cooling coil.

5. The condensate drain pipe has moved and is higher then the drain line. Common occurance when attic work has occured and the contractor or homeowner moves insulation and ends up pushing the drain line up a few inches.

Based on your discription my guess is you do not have a trap on the main drain line. This trap is the same as what you would see under the sink. what this does is prevents air from coming up the pipe once its filled with water. When the air cannot be pulled up the pipe it allow the water to proeprly drain out the pipe.
It is very easy to install. You can purchase these traps at your local big box stores. or simply make one out of 90 degree elbows and a short piece of PVC pipe. 3/4" fittings are used on these. Copy the design of the trap under the sink. The outlet must be lower then the inlet not the same level for it to work its best.