My 2000 Grand Marquis switches to hot air at various times and stays hot and will not return to cold. It will only return to cold after I do the EATC diagnostic check and the code is either 024 or 025. I hit the blue button so the codes disappear and then hit the Max Air and it will blow cold sometimes for days and sometime only for a few minutes (seems like it goes back to hot when I slow down or stop). Is this the blend door actuator?

There is a motor on the blend door that may have went bad and needs repaced this can be accessed by dropping the glove box. It is behind it.

Yes there is a door, and yes it could be stuck.
If one of the ac lines is cold and the other is hot, I would have someone check the blend doors under the dash.

If the blower works but no cold air, a mechanic would check to see if the system is low on freon, then check for voltage at the low pressure switch and the ac clutch as needed.

the blend door in the lwr air vents is stuck it should be down by the squerrl cage also it could be electronically controlled

Is this an automatic temp. control or manual heater control? if it's automatic control,it can be an expensive circuit board which has gone bad. don-ohio

Sounds more like a control valve is not working correctly.. probably stuck in one position because you should always have heat from your heater core...like when you chose fresh air or recirculated air...it switches a valve to allow the change...well from cold to heat there's a valve also that switches the vent inside dashboard

u need to replace the engine thermostat, it is stuck open and the coolant never gets hot.

Have some one watch the heater control valve, under the hood tapped into the feed hose for the heater core, and while you switch from hot to cold they should see movement, if not it has to be checked for vacuum feed and or replaced.

needs re-gassing because one line should be hot (feed) and the return cold , This is a specialist job do not attempt to do it yourself because its extremely dangerous with very high pressures involved

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