Civic 2003, squeal sound when cold and heater ON

I have had mechanic replace three belts in my civic, they are all Honda belts. Right after this, I have heard belt squeal sound, so I took it back to shop and the mechanic tightened the Alternator/AC belt. He says there is no more room to go, it still squeaks especially when the car is not driven for 8-10 hrs and the heater blower is ON. AC is off the whole time due to cold temperatures.

In first few minutes of starting the engine, the heat on and off makes the sound come and go. After it is driven for a while then I can not replicate it by turning heat on/off.

Also when the ambient is warm, then there is no squealing. So in nutshell, two things causing this squeal - Engine is not completely warmed up and heater blower is ON. Can you guys throw some light on what might be causing this issue?

Check your radiator and hoses for leaks and also check the fluid level and make sure there's enough antifreeze in it. If all those things are good, it could be a problem with your water pump.

Check your radiator and hoses for leaks and also check the fluid level and make sure there's enough antifreeze in it. If all those things are good, it could be a problem with your water pump.

I don't understand the connection between water pump and squeal?

FYI, water pump was replaced along with all belts.

I don't understand the connection between water pump and squeal?

FYI, water pump was replaced along with all belts.

The connection would be if there were a problem with the water pump that would cause it to seize briefly or slow down despite the speed of the belt, that would cause the belt to squeal. I've only ever seen this happen twice and I'm pretty sure it wasn't a Honda on either occasion.
However, if your water pump is brand new, this is not likely to be the problem (unless the mechanic f*cked up catastrophically)
You said this happens in cold temperatures... define "cold". The reason I say this is if it's cold enough, your car making some funny noises while warming up is just a given. If your car has been sitting in cold enough temperatures for 8+ hours it needs to be left alone to warm up for 15 minutes or so.

What I meant by cold is let's say first thing in the morning or when going home after work. Meaning if the car has been not running for few hours. In the first 5-10 mins after the engine is started, if you turn on the heater fan in defrost mode, you hear this squeal for 5-10 secs and then it goes away. I can replicate this when I turn the heater fan ON, not always only during first 5-10 mins of starting engine.

Now I have a lot more clarity on this than when I began. It seems, when I first turn on the AC after the car has been not running for a while (cold), I hear the squeal for 5 secs and then it goes away. You can replicate this if you turn on and off the AC for first 2 or 3 times, after that you can't produce this noise. Also when the car is warmed up, then turning ON AC doesn't produce this sound. Does this seem like a AC clutch problem?