Good job coming up with a test power supply.


Didn't you say earlier you'd measured 13.6 Vdc at the solenoid leads, yet now it only switches with an outside source of ~12 Vdc, so I'm still a bit confused.

I actually used a variable supply, it seemed like it was switching at about 14.5V, but when I replaced the connector (with 13.6V) it worked just fine. Maybe it was stuck and the little bit? Time will tell if there is deeper problem with the solenoid itself, or it was simpy poor contact in the connector. But I've cycled 2nd stage (from the thermostat) several times with repeatable results.

I vote for the loose connector.

On several occasions I've driven as far as 500 miles, tightened one or two coaxial connectors a quarter turn or so, resolving a critical manufacturing control system's communication problems, and then driven home, billing each such customer $2-4k per my employer's rates. Customers are happy, and I stay well stocked in steak and beer without having to don coveralls and work a real job.

This may be perfectly normal. At stage 2 the fan speed is higher than stage 1. meaning that there is a higher mass flow of air going across the heat exchanger. So while the temperature differential may be less, the total energy flow is higher. The best way to check is probably to measure the time it takes for a temeprature rise using stage 1 and compare it to stage 2 (from the same starting point under steady conditions).