Mosquito Magnet Forum

So here's a question I've never seen asked here (okay two questions): what could cause a MM to burn too hot, and how hot is that?

I've got a couple of Defenders (both 5-6 years old) and have been playing the "mix & match parts to make one working one" game. I assembled all the guts on the bench, and managed to make it run "manually" by hooking the components to power supplies etc.

While doing this, I also put a thermocouple just inside the exhaust port of the aluminum casting. The temperature I measured there was way higher than I expected, it eventually (after about 5 minutes of running) made it up to 660 degrees F and was still slowly climbing!

But not knowing how hot is too hot, I decided to proceed - put the thing all back together, stuck it out in the back yard, and started it up. About 1/2 hour later, the unit was running and the LED was on steady. But the next morning it was not running and the LED was fast-blinking. My guess is that the controller detected an overtemperature condition and shut down. I've seen some things online that say a MM can overheat when sitting in the sun on a hot day but it was nighttime during this entire run.

What I can't figure out is *why* the temperature would be so high? The unit is completely clean and the mosquito net is empty so airflow is not obstructed (and was even less obstructed when I was running it with the covers off on the bench). Since both air and fuel for combustion are metered, I can't see how it could "burn" too hot unless it was getting too much fuel *and* too much air. The propane nozzle is in good shape, the regulator is new (and I got same results with another regulator), the fan is original...? The aluminum casting is well sealed so I can't imagine extra air is somehow leaking in.

Anyone a) have any ideas what might be going on here and b) ever measured the temperature coming out of the combustor to determine what's normal?

Eric Law

Update: I've been running one unit on the bench, fooling around with "faking out" the control board by using resistors / potentiometers in place of the thermistor.

Found that during startup, when the resistance drops to 13.5K, the LED comes on steadily. So presumably that represents the "low temp limit", above which the controller knows the unit is "burning".

Continuing to lower the resistance, when it hits 3.85K the controller shuts the gas off and the LED starts fast-blinking. So I'm figuring that's the "overheat" point.

Actually running the unit on the bench while doing this, with a meter hooked to the thermistor, the resistance got down to 2K before I shut it down.

So it definitely seems to be running too hot... if only I could figure out why!