Economizers - Settings and basic sequences of operations

[Skyline_GT]

Hey guys, just wondering if anyone can help me with having a better understanding of economizers. I understand the economizers is "free cooling" it works to allow fresh air or cool air to enter through the return of a package rooftop unit. By having an economizers, we can sometimes by pass having to install a low ambient control for the compressor or fan cycling.
I know that Y1 on a two stage system is used for the economizers.
Here a few questions
When the compressor on a two stage thermostat is calling should the damper on the economizer close ?

What settings do most people set the economizers to ?

Guys tell me that set it to "C" for Canada and not to have the damper too open, just enough room for your finger to go through.

I m just wondering if this is right ?
Thx

[Admin]

Using a two stage thermostat with a single stage air conditioner and economizer is fine.  Like you said, use Y1 (1st stage) for the economizer, and Y2 (2nd stage) for the compressor.  With the proper controller and sensors the system should modulate the economizer damper to maintain a certain discharge air temperature.  There are times when the outdoor temperature might be below 65F, but because the indoor humidity is high we need cooling from our compressor.  On colder days we need to control our condenser fan speed to maintain head pressure, so I would always install a low ambient control, or an outdoor sensor that would prevent compressor operation if it's too cold outside.  Typically the economizer damper and return air damper should be mechanically linked.  A discharge sensor, outdoor sensor and return air sensor will allow the controller to automatically control the dampers.