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Old 07-13-2021, 11:51 PM   #1 (permalink)
Ol' Skooler
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Join Date: Jul 2009
Location: Tyler, TX
Posts: 1,176

Beater Echo - '00 Toyota Echo
90 day: 42.67 mpg (US)

Hondizzle - '97 Honda Civic DX
Team Honda
90 day: 46.55 mpg (US)
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I need a bit of scrappy electrical help to get my AC running again

So, things have happened and I am often employed in a pretty hot place, out in the elements, which is medium physical. For the first time ever, I genuinely want my AC to work, and it hasn’t for about a year and a half.

Not sure how to describe what my diagnosis process has been so far. I did a basic resting pressure test yesterday, 100psi at 80*f but after driving it and getting the engine warmed up. It may be low on refrigerant but not low enough for that to be my main issue. Basically I have traced it, so far, to what is marked as the condenser fan fuse, a 20a circuit in the underhood fuse and relay box. It feeds the load side of not only the condenser fan relay, but the AC clutch relay as well. My own paranoia led me to swap relays while I (wastefully) idled the car on my one known good circuit for the cooling fan. No surprise as I got a click from all of them in any position, and all of them ran the cooling fan when requested by the ECM. I pulled the dash fuse for the AC, a 7.5a and it visually checked out. The same paranoia prevailed, so I ohm’d it out and it had continuity.

It had a 30a fuse in the underhood box for the condenser fan already (bought it this way), which was blown. Key on, engine off, a fresh and correct 20a fuse brought the condenser fan online when the blower was turned on and the ac button was activated. However, start the car, and the 20a instantly blew. Car still running, I pulled the 20a and inserted another which again blew the moment it made contact.

I went against my own advice and put in another 30a, curious as the AC worked for a year and a half on that 30a and the car didn’t burn down. Fuse inserted, voila, I got condenser fan and the ac clutch engaged. Compressor seemed to spin with no noise. But that lasted about, eh, 20 seconds.

At this point, if something which is supposed to be nerfed at 20a blows a 30a fuse that quickly, something bad is afoot.

I basically have three possibilities:

Condenser fan is drawing too much current; I’ll have to hand spin the blades tomorrow as a basic check to see how freely it spins. Given that it ran KOEO quite well, I’m fairly confident that it isn’t the problem.

Compressor clutch coil is drawing too much current: this seems borderline. It should kinda act normally until the engine warms up and pours heat into the circuit, and it has to cycle again and again, building up its own heat.

A short to ground in either one of those circuits. This seems the most likely, and not having isolated either circuit, I suspect the compressor clutch circuit given that engaging it is what leads to the swiftest death of the fuses.

Given that I don’t have a scope with amp clamp, any relay jumper tester things (the relays are fine), and I don’t have a Power Probe, how do I go about testing this further? The equipment I do have is the ol’ “scope on a rope” test light, and a fairly basic autoranging multimeter.


'97 Honda Civic DX Coupe 5MT
'00 Echo - dead 2/17
'14 Chrysler Town + Country - the better half's car
'67 Mustang Convertible - gone 1/17

Last edited by jcp123; 07-14-2021 at 12:31 AM..
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