Window air conditioners at our repeater sites are at great risk for plugging and possible burnout due to critters gaining access. Millers are especially troublesome, since they enter the condenser area through the exterior side vents. The fan grinds and disperses remains over the rear condenser core. This inhibits freon cooling and places great strain on the compressor, making it susceptible to burnout.

This was the case at our Baculite repeater site where millers plugged the condenser. A bat and mouse had entered the side vent slots, where their sticky remains further coated the fins. Millers also found a way into the building thru small holes around the AC and were ground up by the inside fan, plugging both the evaporator core and filter. This miller ‘dust’ will make its way into ham radio equipment, possibly causing harm. TIME: 2 at ~4 hours…

Remove the AC to an outdoor table and pull the shell. Open evaporator (inside) circulating fan cavity. Remove motor/fan assembly and its mount. Remove condenser core fan hood.

Compressed air was barely enough to remove debris (be sure to have brushes along and use caution so you don’t bend the fins). A garden hose is much more efficient and thorough. Clean entire AC. After re-assembly, but before installing the shell, ensure the condensate drain hole is open and tape anything that could allow air leakage into/around the interior air flow (evaporator fan) area. Replace shell and ensure AC works properly. Be sure to close the fresh air damper (set to recirculate). If some of the shell vent slots are inside the wall, tape only that portion over so critters can't get in from the wall cavity.

Install AC and thoroughly foam all gaps around it, inside and out. Re-foam later to ensure there are no leaks. Fashion a box of 1/8” wire mesh screen to surround the exterior portion of the AC. NOTE: window screen inhibits air flow, is too flexible and prone to damage! Generously overlap screen joints to avoid gaps. With 1/8” rivets, sandwich the screen between 2 washers. With the board as a guide, bend 2” to 3” flanges in the screen for mounting to the wall. Attach screen by screwing cut 1x2’s over the flanges for strength and so millers can’t enter through gaps. Again, ensure there are no gaps in the screen joints.