Replacing the Dual Run Capacitor
How I replaced the dual run capacitor in my AC unit.
2 minute read · 281 words
For the last few days, the AC would turn on and push air out but the air was not cold. Replaced the intake filter, and the issue still persisted.
Went outside and checked the breaker for the compressor, and it was fine, not tripped, a quick off and on didn't help.
So then I opened up the central AC condenser unit and everything looked fine, did a bit of googling, I found out the most common issue is something called the "Dual Run Capacitor".
Couldn't find the specific model but found one that was similar enough to be a working replacement, the only issue was that it was smaller in diameter than the original.
So I replaced the capacitor and the AC started working properly again, but now how do I make sure that the replacement isn't hanging around inside the casing, and possibly shorting out or causing other issues?
There was already a hose-style clamp inside the casing that was holding the original capacitor in place, but it was too big for the new one. I didn't want to just leave it floating around inside the casing, so I needed a way to secure it in place.
The best solution I came up with was a 3D print, and a little bit of creativity.
All I needed was a circular adapter to make the smaller diameter capacitor into the larger diameter original, with a way to secure it in place with that hose-style clamp.
The following design is a C-shaped adapter that fits around the smaller capacitor. A single slit lets the adapter compress slightly as the existing clamp is tightened, holding the capacitor snugly in place.
// Dimensions (mm)
outer_diameter = 63.5;
inner_diameter = 50.3;
height = 10;
slot_width = 2.0;
overlap = 0.5;
// White lip dimensions
lip_height = 1.0;
lip_out = 1.0;
// Green wall dimensions
inner_wall_thickness = 1.0;
inner_wall_height = 20; // <-- shared target height
union() {
difference() {
// =========================
// FULL BODY (everything that must be cut)
// =========================
union() {
// =========================
// Main ring (orange)
// =========================
difference() {
cylinder(
h = height,
d = outer_diameter,
$fn = 200
);
translate([0,0,-1])
cylinder(
h = height + 2,
d = inner_diameter,
$fn = 200
);
}
// =========================
// Inner wall (green, 20mm tall)
// =========================
translate([0,0,height])
difference() {
cylinder(
h = inner_wall_height,
d = inner_diameter + 2 * inner_wall_thickness,
$fn = 200
);
translate([0,0,-0.05])
cylinder(
h = inner_wall_height + 0.1,
d = inner_diameter,
$fn = 200
);
}
// =========================
// 180° TOP LIP (white)
// =========================
translate([0,0,height])
intersection() {
difference() {
cylinder(
h = lip_height,
d = outer_diameter + 2 * lip_out,
$fn = 200
);
cylinder(
h = lip_height + 0.1,
d = inner_diameter,
$fn = 200
);
}
translate([-200, -200, -1])
cube([200, 400, lip_height + 2]);
}
}
// =========================
// SINGLE SLIT (cuts EVERYTHING)
// =========================
translate([
inner_diameter/2 - overlap,
-slot_width/2,
-1
])
cube([
(outer_diameter - inner_diameter)/2 + overlap,
slot_width,
height + inner_wall_height + lip_height + 5
]);
}
}