I know this is covered several times but... Even if your AC is dead you likely still need to clean before crap causes a fire from junk in/near the resistor pack.
I've clean my heater/ac box before (a few years ago) and still get crap in there even when I don't drive much and don't park under trees.
Found because I had to replace the blower today... Doesn't look bad right? (Pictures from a small camera turn sideways thru heater blower hole then rotated/etc to show here.)

Remove resistor and carefully stirred up the crap... Looks worse now because shape of box hinds more.

then carefully used a vacuum thru the blower hole.
end result (Little out of focus but not taking blower out again.)


Note the bend fins from earlier cleaning...
Many don't have a screen to protect the AC evap and very easy bend the fins even when you're careful.

Best way to clean w/o taking the box completely apart:
Remove the blower and use a camera to look at resistor area. Use the camera to see your work too. Any small camera w/ a screen to show pictures taken make this easier.
When cleaning is needed then:
A. Remove 2 screws and the resistor pack to clear the space to clean.
B. Carefully stir the crap using blunt piece of soft wood or plastic. Avoid hitting the AC even then.
C. Suck out the junk. Slide nozzle/hose against the floor and/or front wall to prevent AC fin damage.
Repeat B and C as needed.

If you have mold etc stuck to the AC then try soft brush to loosen that but make sure vacuuming in done outside or have HEPA filters. You don't want to breath this.

After you're done turn on blower at full speed out side and doors open to blow out the box. Many times you still get loose crap blown out the vents after work on the box.

I tried just removing resistor pack but even with something to stir up crap can't reach all then suck out the resistor opening.

I have a heat only box in a parts car that I'll take picture inside later. Not sure if they have same level of this problem.
AC Evap is slanted in the box so airflow forces most junk to the resistor side. Heat only boxes are different.
Even if heater only box doesn't push crap to the resistor like above, you want to clean them anyway.
Sometime a leave get into the resistor then fries and ashes/embers falls into other junk and starts a fire.

Another note:
Cleaning the AC box helps smells after using AC. Moisture run off quickly grows mold to start then add rotted leaves etc...
You can use same method on many cars not just Fiero. Even some cars w/ blowers under the dash in the car.

------------------
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(Jurassic Park)

The Ogre's Fiero Cave

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[This message has been edited by Spadesluck (edited 10-25-2018).]

Here's heat only box inside, pic thru blower opening on my parts car... There is a door, hot/cold door I think, that closes heater core there. (Control head inside of car is missing.)



Seem like heat only box is more open to let a lot of crap thru unlike AC/heat box above that pushes crap towards the resistor. I would clean it if you pull the blower for any reason but doesn't look as bad as a fire hazard for most things.
Resistors look better because how it's made but small junk may get stuck, pic shown some burn crap (and some cob webs) on the resistors, and so cleaning out all crap can help.
If mice etc moves it you must clean and use Lysol etc too.
Not sure how you can clean the door... Old Foam likes to fall off making a bigger mess to deal with.

You can pull the blower on both boxes in minutes so checking/cleaning is fairly easy. 5 7mm hex head screws and 2 power connectors. Both have same blower and fan but is a bit tighter to remove in AC car w/ spare tire in. You do not have to remove sun roof shelf to remove the blower or the resistor set. AC cars can be easier when you have a long 7mm nut driver or socket extension. Magnetic tools help too.

If you can, remove the blower nut to check under the fan. Sometimes things get stuck between motor and fan and rub the fan and can be intermittent noise problems.

[This message has been edited by theogre (edited 10-26-2018).]

Are other types of cooler operating resistors available that could replace the original incendiary style?
The debris should still be removed but the fire hazard might be mitigated...

[This message has been edited by David Hambleton (edited 10-26-2018).]

[This message has been edited by Spadesluck (edited 10-26-2018).]

quote Originally posted by David Hambleton: Are other types of cooler operating resistors available that could replace the original incendiary style? The debris should still be removed but the fire hazard might be mitigated...

Not really. This setup is still used but have thermal fuse(s) to cut power for overheat from low/no airflow. The fuses often won't blow for a leaf getting stuck in/on them. Some add a metal "screen" to keep out such things and maybe could make that but make sure the screen can't cause a short or reduce airflow over the resistors.
Others just use better, often more expensive, resistors that's close to many problems but many are bigger then the resistors here.
Still Others have MOSFET(s)/transistors to act as resistors but changing to this setup much harder.
google heater blower resistors and look at many images. (Thermal fuses are small cans size of 1/2w to 1/4w resistor.)

Finding a replacement resistor set w/ right values is tough because no-one publish that data for selling parts. Often not even in FSM and other books covering repairing heat/ac. The blower speed affect airflow to rest of systems and cool the "resistors." DIY Replacement/"Upgrade" may cause too low speed and that can cause other problems and oven heat the "resistors." "resistor" here because including MOSFET and other method to control blower speed and need blower air to cool.

Many current vehicles have 2 speed rad fan same as 84 Fiero w/ AC w/ a better resistor somewhere on rad fan motor or fan shroud.
Example: from a wreck 2007 Kia, resistor was in the corner of the shroud.

CLICK FOR FULL SIZE

ETA--> Heat is a function low resistance and amps used in the resistor. Is why rad fan resistor above is likely rated < 1Ω @ 50w or more. (Resistor is 1 5/8" long, 1" diam.) Even 84 Fiero rad fan resistor is 0.3 Ohm @ 50 Watts, Wirewound in Ceramic shell. Heater blower resistors is similar w/ most or all < 1Ω. MOSFET etc doing same job puts out a lot of heat too and quickly fries w/o blower airflow to cool the small heatsink. All need a lot of air to cool and w/o that would likely need to double or triple the watt rating and mounted the part to heavy metal far for plastics etc.
Even Fiero Dash Dim transistor is bolted to dash frame away from plastics that can melt or worse. Than only handles ~ 5 amps of dash bulbs and still can burn you if touch it.
Many have use 6Ω 50w w/ aluminum case for LED "upgrades" that eat ~35w at 14v. Most are only rated at 50w with mounted to a heatsink but most buyers don't used them in a car and can melt or burn things near by because they are overheated.

[This message has been edited by theogre (edited 10-27-2018).]