My wife's 05 Malibu Maxx heater has gone out. fuses good. blower good. no warm air. makes weird noise under dash when i play with AC/heater vent control. i am thinking the blend door actuator may be bad but i don't know where it is or how to get to it for that matter. what is a good source to go to for a schematic so i can repair/replace this thing?

you unhooked it underneath

Test the electrical circuits ! Manual HVAC or automatic HVAC ?
Do you know the difference ? Heater / A/C blower motor electrical control diffrent . Manual has resistors an a relay for different speeds , automatic has a blower motor control module .Free wiring diagrams here http://www.bbbind.com/free-tsb Enter vehicle info year , make , model and engine size . Under system click on HVAC ,then under subsystem HVAC controls will pop up . Click the search button , then the blue links . First off you need to know what system yours has , manual or automatic.
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First check all the fuses. There should be one for Blower or Heater. If all fuses are good, It is likely a bad blower motor or a switch to turn on the blower motor. Try all fan speeds in non auto mode and see if you get any activity. If you get activity on some fan speeds then it is the switch or sometimes called the blower motor resistor. If no activity, its time for a new blower motor. They are under the dash usually on the passenger side, shouldnt be too hard to pull out.

HI. Here is a complete check list that will help you trouble shot this issue. You will find the problem in one or more of these areas stated below.

1. Check Drive Belts - The air conditioner utilizes a drive belt that supplies power to rotate the compressor, which is basically a refrigerant pump. If the belt fails the compressor has nothing to drive it, inspect and replace as needed to restore operation. If belt is intact proceed to the next step.

2. Check for Compressor Clutch Engagement - Turn the air conditioner to the "on" position and set controls to the coldest setting. Start the engine and allow to idle. Then open the hood and inspect the clutch at the front of the compressor, is it turning? "Engaged" if so, the system has enough refrigerant to activate. If the system is low on refrigerant it will not work properly. In this case an air conditioner recharge kit is needed to recharge the system. If the system is low on refrigerant it could cycle on and off, making a ticking noise. If the compressor clutch is not turning proceed to next step.

3. Inspect for Refrigerant Leaks - If the system has a large leak and no refrigerant remains it will not activate. First test system for a static pressure charge, with the engine off attach an ac gauge to the low side pressure port and check the state of charge. Depending on outside temperature there should be between 50 psi and 80 psi. (Cool and warm). A refrigerant leak detector is needed to inspect for leak, but if you do not have a leak detector there is an alternative method. The air conditioner system is designed to run with oil suspended in the refrigerant to lubricate the system. Check for oily residue outside the system by inspecting all hoses, compressor, condenser, evaporator or receiver drier and replace any component that has failed.

4. Inspect Fuses - Check under dash panel and under hood power distribution center. Replace failed fuses as needed, recheck system. If the new fuse fails when reinstalled a short circuit is present and requires diagnosing with a wiring schematic, follow circuits to locate short, repair as needed and recheck system.

5. Check Temperature Control Vents - The vents inside your car are controlled by a cable, electrical servo or vacuum servo. If the temperature blend door is not functioning properly it will cause warm air from the heater to exit the vents. To check this start the car and allow the engine idle, next turn the blower motor speed on low, switch the temperature control from warm to cold while your ear is close to the vents. You should hear the door move inside the heater box as it swings from open to close. If not, insect for a vacuum leak or a shorted motor in the servo, repair the leak or replace the servo motor.

blower relay or resistor bad.also the AC and HEATER control switch could be bad.

i had this exact same problem with my 98 explorer. your blend actuator (blend doors) are not morking. these are on the passenger side under the dash. getting to them will be dificult, but it can be done. you will need to take apart the heater box, to fix them. (the big black box under the dash).

sounds like the blower motor, Get a test light and hook it up to the wires going to the motor this will tell you if power is getting to the motor . Hopfully it is , Just pull the panel off on the pasangers side under the dash and you can see the motor . It's easy to change and should fix the problem. If you get no power it check for power at the switch on the dash . It could have gone bad !!

Potential easy solution; check whether there is a vacuum operated valve in the heater supply or return lines. My old v8 '84? Malibu had one. It kept coolant from circulating through the heater until the motor warmed up; helps warm the engine quicker; BUT it was stuck closed and I had no heat. Rather than purchase a new one or mess wqith the vacuum lines, my solution was to use a piece of wire (nylon zip tie might work also) to hold the thing in the open position. So the motor takes a minute longer to warm up. Else might be air embolism in the line, which could indicate combustion leak or insufficient purging of air from the system after you changed the t-stat. Good luck.

One suggestion. Have you checked the fuses ?

I would check the AC or blower fuse to start with. If you have the drivers manual it will show you where the fuse box is. Typically there are at least two boxes to check. One in the Engine compartment and one in the passenger cabin.

Look inside the lid of the fuse box to see which fuse may apply to the AC circuits or the blower and check to see if they are blow. the metal link between the two posts that plug in. If the link is missing you need to replace the fuse with one of the same rating. Make sure you know where you took the fuse out from and put it back in the same slot if its good. Check all the main fuses if possible to see if any have blown and replace if they have.

The blend door in the heater box itself is what directs the air to where it needs to go as per selector switch. The heater box is located under the dash.