There may be some drag on the AC clutch when it is disengaged as the clutch 'free-wheels' during this time. When you engage the AC ,the clutch 'locks up' and the noise disappears. If the noise gets worse you may need to replace the clutch, if it stays the same and it not very loud, I would not replace it.
why 2003 ford focus stall when air conditioner is turned on
You have no wheels. - Geoff
How do you turn of the engine on a new ford focus
The engine will cause the hood to get hot. That is fairly normal.
There are pages and pages of things that can cause a check engine light. You need to have it checked with a scantool. Then the code can be diagnosed and repaired.
Do NOT use Diesel fuel in a Ford Focus. The engine will stop running and you will have to drain the gas tank to rid the car of the diesel fuel. Gasoline engines are not designed to run on diesel. They do not have enough compression to cause the diesel fuel to combust The only engine used in a 2000 Ford Focus was the 2.0 which is NOT a diesel engine.
The 2010 Ford Focus has an inline 4 engine.
The 2006 Ford Focus has an inline 4 engine.
The 2011 Ford Focus has an inline 4 engine.
The 2005 Ford Focus has an inline 4 engine.
The 2014 Ford Focus has an inline 4 engine.
The 2004 Ford Focus has an inline 4 engine.