A few days ago, while acquiring data, I inadvertently interrupted the AC power to the old Defender, resetting the trap. Power interruptions happen all the time here, but this one somehow changed something, I don’t know what, and the normal operating temperature rise from the intake to the exhaust increased dramatically from ~85°C to ~94°C. Surprised, I tried cooling the trap to near ambient and restarting, but the thermistor temperature rose and stayed high, in the 130° range, close to the 140° limit I had set.
Puzzled, I reviewed my notes and blog entries, and discovered that this was a very typical range 2 years ago. I might have been using the wrong nozzle at that time. Since the change, during the last two days, the trap had caught only 20 mosquitos (although I didn’t see any around), compared with several hundred in the previous day (although just after a rain). The trap was running at about 128° with an ambient of ~34°, for a 94°C rise.
I then tried the electric tire pump on the Schrader valve, and it read 105 psi, which is very high. I ran the pump for several minutes, but there was no change in pressure – nothing was dislodged. Restarting the trap, the temperature rose even higher to almost 135°C. I had made it worse. It may not be a good idea to use an flaky auto tire pump to clear out a hot trap. Perhaps the contaminants from the worn-out oil-free pump have really clogged the nozzle, although the pressure went up high and stayed there. In any event, the nozzle had to be cleaned or replaced.
I found an old nozzle that had been cleaned and had a like-new 40 psi test fixture result. I was determined to change the nozzle as quickly as possible, no frills. Fortunately, I have a high torque electric screwdriver, so with that plus 2 large slot screwdrivers to open the combustion chamber, and nothing else, away I went.
Fortunately, the awful top case screws are long gone to a better place. Power off, remove the basket and top cover, unzip the 3 sheet metal screws into stripped plastic supports, unscrew somewhat the two hose clamp screws, remove the power jack, remove the solenoid from the valve, and it all lifts out. Turning the assembly on its side, remove the 3 machine screws holding the plastic exhaust port from the combustion chamber, then the last 5 screws holding the chamber together. Taking care to not break the circuit board, NodeMCU and other stuff, I used the two large slot screwdrivers to pry the case apart, and it popped open without too much effort. (I had a few times back in the past given up on applying new gasket sealer to the case, the old stuff seemed to work just fine, and nothing looked like it was leaking out, so there.) The nozzle assembly came out with some rotation, and then I replaced the nozzle. Reassembly occurred, but not before using the hose to spray the awful remains the last couple of year’s catches.
A bit of DeOxit on the power connector to try to address the intermittency, and, amazingly, the trap started without issue. The connector is still intermittent, however, but this was not the time to fix that. The mosquitos scored 2 bites, maybe real, perhaps imaginary bites. Not bad.
The trap with the cleaned nozzle went up to 127°, a 96° from 31°C rise, but has since calmed down to 124.6 – 33.1 = a 91.5°C rise. I don’t know whether this is a better operating point or not, only the catch rate can tell this, but at least a clogged nozzle has been changed. I have been measuring tank weights and catches for 3 days now, another post will provide some results.