Automotive fuse in place of glass BUS? Ok?

Old 11-10-15, 05:23 PM
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Automotive fuse in place of glass BUS? Ok?

An HVAC technician replaced an older Trane fuse holder, and the fuses that went into it - "Time Delay; Amperage Rating (A): 3-2/10; Voltage (AC): 300; Bussmann One Part Number: GMQ-3-2/10"

With an automotive, modern fuse holder and fuse (3A). He explained that the older ones are about $8 a piece and these are $0.30, and it was cheaper to replace the blown fuses as we kept diagnosing the issue.

While it worked for the A/C, now when I switch to heat that fuse keeps blowing. I've gone through three, and then from a 3amp to a 5amp, and it blew also. Not wanting to try higher amperages, I wanted to ask if this is a legit fuse/ fuse-holder replacement and if this fuse setup should work. And if the 'heat' setting is drawing more current and thus causing the fuse, which seemingly worked fine for A/C, to now blow. Also, what impact does the "time delay" descriptor for the older fuse have in my case, and could that be the culprit.

Thank you for any advice, suggestion.

Old 11-10-15, 05:47 PM
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Automotive fuses are rated at 32 volts and should not be used for line voltage applications. Not sure if your case is 120 volt or 24 volt. You can't trust a 32 volt fuse to not arc over (if used on 120 volt) after blowing and maintaining current flow when it shouldn't.

But your problem is probably caused by not having a time delay or slow blow fuse. This type of fuse resists blowing on short surges and overloads as might happen when a motor is started, etc.

Without knowing what the fuse is protecting, it's hard to say whether higher current draw in heat mode is normal, but it's certainly feasible. For example, the gas valve may be on the circuit and wouldn't be operated in cool mode.

If you have a multimeter with a 10 amp range could try measuring the actual current flow to be sure this is a transient condition blowing the fuse and not some real problem.

If I were you, I'd go back to the factory style fuse, assuming you have the original problem solved.
Old 11-10-15, 06:30 PM
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I agree with kpytoi1 's tech. It is a great idea to replace that odd GMQ-3-2/10 fuse with an automotive 3 amp fuse. I have done this many times.

( prices ~ 7 years old)
Old 11-10-15, 09:36 PM
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The ATC-3 fuse is perfectly ok. DO NOT sub in a 5A as you risk blowing the transformer out.
You need to figure out what is causing the short. A Trane heat pump requires 24vac to switch to the heat mode. That would be what I'd be checking. A shorted cable from air handler to condensor or even a shorted reversing valve wire right inside the condensor.

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