Airflow on Quest M3s

Discuss roast levels and profiles for espresso, equipment for roasting coffee.

#1: Post by TonyC »

I see many folks with Quest M3 discussing airflow management techniques, including the opening of the bean chute or the back cooling tray to minimize/stop airflow during soak/dry phase. On my M3s (2017) fan still runs with knob in fully off position, so stopping airflow is of interest.

Has anyone noticed a difference between opening bean chute door vs. back cooling door to stop airflow on M3s? Is one preferred over other for some reason?

Also, some recommend clipping the the wire on the resistor on the airflow circuit, and if so, does this accomplish the same as opening either door on machine? Would be interested in any thoughts with these three ways to stop/minimize airflow on the M3s, and when you most often do this. Thanks all!

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#2: Post by Nunas » replying to TonyC »

Opening the 'back door' effectively results in no blower, as the low pressure needed to suck the air through the roasting chamber can only be created with the lid closed on such a huge opening. With the bean chute door open, you'll still get a bit of air, as the size of the aperture is about the same as the size of the hole in the back/bottom of the roaster (on Mk-2s anyway).

Cutting the resistor gives a true no-fan setting, as once it is cut, the fan will only begin to turn when the control gets near a setting of 4. That said, I'm not of the opinion that this is a good idea. It essentially allows the MET to reach extremely high levels. It also allows moisture from the drying beans to remain in the roast chamber potentially 'steaming' the roast. I believe my idea for a modified fan control is better A Better Quest Blower Control Mod In essence, the resistor you are referring to is replaced with a trimpot. With careful adjustment, one can have nearly no fan (or no fan) at zero on the control, and a high fan at the other end of the control. This is a lot finer fan control, as the speed varies gradually over the whole range of the control, instead of from 4 to 8 (the max position of the control).

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TonyC (original poster)

#3: Post by TonyC (original poster) »

Thanks for response, and have seen this post, and looks like a good solution. Unfortunately, I am not 'overly handy' w/soldering things. Could you share a good source for the 470k pot, and perhaps a close up or two w/additional detail on where to specifically connect on the back of the fan pot (recall I have 2017 M3s, but think the pot looks similar to your M6? Also, not sure what a 'wiper' is ... and/or locations to attach. I will be doing a deep cleaning on my M3s in a couple of weeks and can send pics if that would make this easier?
Thanks for follow up!

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#4: Post by Nunas » replying to TonyC »

Probably Radio Shack. If you don't have one near you Amazon has them by the dozens. Here, for example, ... GMQV&psc=1 The value is not important, anything over about 300k will do.

As for wiring, it's dirt simple. Here is an image of a trimpot/potentiometer (same thing but trimpots are tiny versions).

So, to add this to your Quest, if you have a resistor across terminals 1 & 3 of your blower control (i.e., your fan has no off position), clip it out. The trimpot takes its place. Solder either pin 1 or 3 of the trimpot to one end of the existing control and solder pin 2 (the wiper) to the other end. Nothing gets soldered to pin 2 (the wiper) of your existing control. Once you have this installed, then turn on the Quest and set the existing control to zero and the heater on full. Then turn the trimpot control until the fan just starts (or just stops if you want an off position). The fan speed will vary a bit when changing the heater control, but not much. I hope this helps!

TonyC (original poster)

#5: Post by TonyC (original poster) »


Thanks, so that I am clear here, the left image is the blower control (or similar) on the Quest M3s and the right image is the trimpot? My M3s still has fan blowing with the control turned all the way off (counter-clockwise), so that means I should have a resistor between terminals 1 and 3 in left image? Clip this out. Then solder tab 1 or 3 from the trim pot (right image) to tab 1 or 3 of the blower control (left image), and then pin 2 on the trim pot (e.g. wiper) to the other end on blower control (tab 1 or 3 that was not previously used). Does this sound correct? Also, does it matter which direction the trim pot is wired in (e.g., tab 1 from trim pot to tab 1 on blower control, then tab 2 on trim pot to tab 3 on blower control, OR tab 2 from trim pot to tab 1 on blower control and tab 1 from trim pot to tab 3? Key is to make sure tab 2 of blower control does not have anything from trimpot wired to it. Sorry, for lack of understanding, but want to sure I have it right before cutting things out.

Also, since I have not attempted this before, are tabs on trimpot pretty obvious?

Thanks again and assuming all of this is correct, will just make changes during next deep clean! Will report back....

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#6: Post by Nunas »

Hi, I think you've got it. The left is a standard potentiometer, and the right is a sort of schematic diagram of how they work inside. From pin 1 to 3, the resistance is fixed at the value of the pot. From 1 to 2, or from 3 to 2, the resistance varies according to the rotation of the shaft (wiper). No, it does not matter where you put the wiper, nor does it matter whether you use pin 1 or 3. Hooked one way, clockwise will be up and hooked the other, the reverse. Once you get it adjusted, it won't really matter which way you turned it. It does not matter what brand you buy; the middle pin will always be the wiper. The tiny ones have one pin offset; it's the wiper. The pins are reasonably robust. You can clip out the resistor and solder the trimpot in its place.