A One-Day Job Turned Into A 2-Week Job Because Of A Single Word

This is a story about how something can be right in front of your face the whole time, but you can’t see it because you’re looking for it by a different name...

About 1.5 months ago, the A/C compressor on my wife’s 2009 Mazda 5 seized in a belt-breaking, bearing destroying disaster. I was a bit annoyed as I had just replaced it 14 months prior with a new replacement. Unfortunately, it was a China made hunk of junk that was the cheapest I could find. I got what I paid for.

Not my Mazdaspeed5, but I wish it was....And I needed a catchy photo for clicks.

So I ordered a new compressor (Still made in China, but this one looked a little better of build quality) and all other associated parts (drier, expansion valve, belt, oil, refrigerant). A couple weeks ago I once again replaced all the parts, ran a vaccuum pump on the system for an hour and held it for another 1/2 hour to ensure no leaks. I then added the refrigerant and expected everything to be back up and running, blowing out nice cool A/C to combat this unusually hot Buffalo, NY summer.

That turned out not to be the case. Try as I might, I could not get the A/C compressor to engage. I checked, and rechecked everything I installed. I had 112psi on the low-side which is more than enough to start cycling the compressor. I checked both the underhood fuse panel and the dashboard fuse panel to ensure no blown fuses. The ‘A/C’ fuse in the dash was fine, but I couldn’t find any ‘A/C’ fuses in the underhood box. I also checked the relay and replaced it with a known good one. Nothing I tried worked.

I had to give up the fight for a few days because my wife need the car for work and to take the kids to Pittsburgh. In that time I started doing internet research to see what was wrong. I wasn’t able to find a whole lot pertaining to the Mazda A/C system. This left me thinking that it’s either something quite simple or something incredibly rare and complicated that I’ll probably never find.

Our Mazda 5 in all it’s dirty and (now A/C operational) goodness

Over the next 1.5 weeks, I started testing all the wiring. I discovered that if I bypassed the relay with a jumper wire right from the battery, I could engage the A/C clutch. At least that confirmed that my new compressor wasn’t the culprit. I also tested the low pressure switch and that was working as I could get the fan running at both low and high speed.

I started to get serious about tracing wires and I finally ran across THIS THREAD on the Mazda 3 forums (The Mazda 5 and Mazda 3 are pretty much the same car wiring-wise). I printed off the diagrams and told myself that I’m going to get this figured out. I will be the first to admit that I’m not a big fan of electrical work and reading wiring diagrams is a bit confusing. I managed to determine that the relay gets its power from both the dash controls and the battery. Both need to be sending power to the relay to get it to work.

Wiring Diagram: These things work!

So yesterday, I finally get a chance to look under the hood and start going over and inspecting the whole circuit. After some playing around, I realize something:


I never found a fuse in the underhood panel, but this diagram indicates a 10a fuse in there ........

I look over the ‘map’ on the fuse panel cover over and over and I still can’t find anything A/C-related other than the relay, which I have checked multiple times already. While I understand that this is a Mazda 3 diagram, I still think to myself ‘There’s obviously a fuse here and I’m just missing it’.


I decided to start pulling out every fuse and checking them one by one. I get about 3 fuses in and something catches my eye...


The wiring diagram I have indicates the fuse as ‘A/C MAG 10a’. I look back at the box and I see the fuse location for ‘MAG’. I start laughing out loud followed by a ‘You’ve got to be fucking kidding me!’ and I pull that fuse out. Not surprisingly, the fuse is blown. I replace it and the A/C clutch engages and my wife’s car is now blowing nice and cool air inside.


Now while I am laughing at my own stupidity that something so simple took me so long to discover, I am also absolutely flummoxed as to why Mazda did not label that fuse in some other way. Sure I understand that ‘MAG’ is probably short for the electromagnetic clutch that engages the A/C compressor, but seriously, they couldn’t mark it ‘A/C MAG’ on the panel-map??

‘MAG’, because ‘A/C’ would make too much sense.

With that one simple change, I would have diagnosed and discovered the blown fuse in a matter of seconds because ‘A/C’ is what I was looking for! Who looks for the word ‘MAG’ when trying to diagnose A/C issues (Besides a Mazda-tech of course)?

Oh well. At least the A/C is fixed. Of course its after all the family trips are done for the season and the weather is now cooling off.....

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