No pressure is there a removable pressure restrictor?

Most modern shower restrictors are permanently fixed and require some prying with a pick or small screwdriver and possibly drilling. Be careful that in removing some of the pressure reducing stuff you do not slip and put a hole in yourself. You don't have to get it all out, just enough to allow full pressure to the head.

Hi Fran:
Most shower faucets now are equipped with flow restrictors. It is possible with some units to remove the flow restrictor plate from the shower nozzle. It has to be dis-assembled to do that.
Regarding the lack of hot water, that would usually be a different problem and will be related to the hot water source.
Hope this helps.

The problem is that all shower heads sold now have to be low water volume. You can take the restrictor out and see if that helps. Look for a blue or white plug type insert in the fixture that has a slot on it. Pull it out and you should be good.
http://homeguides.sfgate.com/remove-water-restrictors-showerheads-27817.html
and http://www.ehow.com/how_5189790_remove-flow-restrictor-shower-head.html

My assumption is this is the A/C compressor, First remove the freon for the system, you will need a special tool to disconnect the A/C lines, The parts you will need are new Compressor/w clutch and dryer, freon and refrg oil o-rings for a/c lines new restrictor for high pressure line. remove comp and dryer replace with new and proper amount of oil in compressor, replace high pressure restrictor and o-rings on lines once the system is completely together you will need a A/C vac pump to create a vacuum in the system be for the refrig is added to proper pressure for vehicle Compressor

I don't think it is the flow restrictor. I am guessing your water pressure is on too high. That would cause the whistling.

Elisa Jed ' http://www.kookaburrakitchens.com

Your problem is in the water restrictor located inside the shower head. All plumbing manufacturers install these small plastic internal blockers to reduce water down to 2.5 gals per minute. In your case, this restrictor is most likely filled with sediment which is restricting it even further. Remove the shower head from the curved shower pipe. Look inside where the water goes through it. You should be able to see the restrictor. Maybe you can flush out the sediment. Otherwise, remove it and I'm sure you'll get more pressure then originally installed. Because most restrictors are sort of plastic screens or cones, I usually put a wood screw through the center of this product and then once a few threads bite in, I use a plyers on the head or the screw and pull outward while holding the shower head in a stable position. If you are able to get it out, technically your "out of code" because now your going to get all the water it can really supply.Most people are delighted to have it gone.
Nimsgame

Your issue could be caused by the water restrictor in the shower head. To know for sure, remove the shower head and then turn the water on.

Very tough water restrictions have manufacturers using plastic water restrictors in the shower heads.

Although you are not supose to, some shower heads can be taken apart to modify, or remove the restrictor.

I hope this helps you.

How I remove them is take a drywall screw and screw in to the flow restrictor. Then grab it with a pair of pliers and pull out.

yes it should have a flow restrictor in the end of the spout. You might need to clean it out

All you should need to do is remove the shower head and make sure that their isnt any dirt obstructing the opening ,also if their is a restrictor like you said you need to remove it.This should make a big difference.