Where can i get a copy of the parts that make up the air suspesion of my 2001 grand marquis. sometime it works and other time it will not.

SOURCE: 2000 mercury grand marquis air conditioning won't work

1st Thing,
Located Someone With a Set Of A/C Gauges 134A Freon,
Make Sure Your A/C System Has Enought Freon In It, There Is a Low Freon Pressure Switch
In The Electrical System, Usually, 50-60 PSIG or Less On The Gauges, Will Indicate Low Freon, When Freon Is Low The Compressor Is Dis-engaged To Prevent Compressor Damage.
1] Low Freon
2] Bad Low Pressure switch
3] Blowen Fuse[s]
4] Electrical Problem[s]
[a] Digital Climate Controlled ?
Climate Control Self Diagnose From Button's On Unit, OEM Manual Explains This,
If Yor Auto Has Digital Climate Control.
5] Bad Compressor DC Coil

Note: Does The Compressor Engage, Click-On When Button Is Pressed, But Getting
Only Warm Air?
Is One Of The Compressor Aluminum Tube's Cold, Be Careful Other Is Really Warm/Hot,
If Cold and or Sweating, Dripping Water [Normal], You Are Blending Hot Air w/Cold
Air At The Heater Blend Box, Making Warm Air.
If This Is So, If A Vaccum Controlled Temp Unit, Check For A Vaccum Hose Bad,
Should Be Either 1or 2 Vaccum Lines Going Into Firewall To Feed The Controller
Unit, If OK, Might Be a Bad Blend Box Diaphram, [Control's A/C air, Blocks Off
heater Coil Hot Air].
If Your Auto Is Vaccum Controlled, Can You Changed From Bottom, Dash,
Defrost Air Flow?, Yes, No Vaccum Lost Feeding Controller, Still Might Have
Bad Diaphram Blending Hot Air w/Cold If Your Have Cold Alum-Tubing In
engine Compartment.
If Digital Climate Controlled, Might have Diaphram's, Vaccum Controlled or
electrical Servo's Controlled vs Diaphram [Vaccum] Controlled.
This Might Help, Hopefully, This Is Just For Starter's, There More To Some System's
and Without The OEM Mgr's Manual[s] You/Be Would Be Lost, especially w/Electrical.
Later, God Bless

SOURCE: When I set the thermostate temperature for heat it

Sounds like your heater core is plugged. I would recommend having your coolant system flushed by a certified garage.

SOURCE: my 2001 mercury grand marquis blows only slightly

check the thermostat values if correct to manufacturer,

SOURCE: Does a 2001 Mercury Grand Marquis Ls Have Stock

Yes It is standard on Top end versions and optional on the base models.

SOURCE: Is it a fair price

That's way to much, here at my repair shop, we charge $550.00 with tax, take it to an indenpened shop for repair's, you will get the same warranty, if not better, and no not a fair price, you could almost buy two fuel pump's with labor if you let the dealer do it.