hi all,
just having a issue with my air con its been recently gased but started my car this morning and a screeching sound is coming from engine bay and its only when i push my air con button on that it makes it screech.

Any info would be much appreciated

Is it really loud? It sounds like the compressor doesn't want to turn when the clutch is engaged and the belt is just slipping over it.

sounds like compressor may have seized -
was engine cold or operating temperature -
remove belt start turn A/C on...try to turn compressor pulley by hand if you can't compressor will need to be replaced (and maybe tx valve plus dryer gas etc)

may have been over gassed causing it to seize when Hi side pressure builds up to hi but normally doesn't do this until driven for awhile on a hot day (degas and recharge with correct amount)

I looked at the belt going around the compressor pulley and its still turning . Maybe my compressor is counting down its last days of functioning. As you can hear the compressor kick in and seems to be still functioning? but makes the screeching noise as soon as you push the air con button .

is noise from compressor ? - check compressor clutch for slipping /damage /metal filings etc

ok thanks will do

sorry guys but on a closer inspection I've noticed that my tension pulley is slightly on a angle and looks like that might be the cause

Remove the belt and spin the pulley, you will soon know when it is stuffed.

Even if the pulley in knackered it should make no difference if the AC is on or not.

Have you removed the belt and turned the AC Pulley with the AC turned on as suggested by TedW?

Manually spin the front clutch plate (not the pulley), if it rotates without binding, the compressor scrolls are probably okay, if you're saying you're getting cooling.
Sounds like the plate is slipping against the pulley face when engaged, the faces will be probably burnt, so you'll need to pull off the clutch plate, and emery paper on a flat surface/wire wheel them up.
There is a spacer washer for the clutch plate, you can leave it off when assembling - I've found it can cause too much clearance in some instances, causing the plate to not engage properly. Just make sure you can see daylight between the plate and pulley, and the plate isn't catching unengaged.

Finally, if you have a front shaft seal leak, you'll find oil between the pulley and plate, meaning the system is losing gas, as well as squealing.

thanks for the help much appreciated