I have a Danfoss/Isotherm air-cooled icebox
conversion system, which i think is pretty common. It has worked fine for the 5 years that i've owned the boat
, and for a long time before that as far as I can tell, but recently it has begun acting up.
I have been searching the forums
and reading Richard Kollmann's website and posts here, but I don't see anything that matches this exact problem. I am wondering if it is a problem with the thermostat or with the controller perhaps.
Symptoms: quick-cycles when it reaches the set temperature.
IE: everything seems fine, but when it hits the set-temperature, it cycles on-and-off every 30-seconds to 4 minutes or so (seems like random timing) - it will start up and run, then shut off abruptly, then start up immediately again, then shut off, etc. If the thermostat is turned to a higher number, it runs longer, makes the box colder, and then cycles quickly again. Set it to a lower number?
It appears as though whatever tells it to wait a little while once reaching the set temperature is no longer waiting, just trying to always hold it at exactly the right temperature?
problems with the installation
- The thermostat is installed _outside_ of the icebox - normally it shoud be inside, correct?
- the thermostat sense wire was not mounted directly on the evaporator - it was mounted on the plastic "back" of the evaporator... moving it to be in direct contact with the evaporator has not caused any change
- the insulation isn't very thick, particularly in the lid
- the batteries are very weak, but i have the same problem on shorepower, I don't see the "low battery" code flash from the Danfoss controller, and it runs fine if I jumper around the thermostat - it's happy running, just having trouble choosing when to run and not run...
- the sense tube was touching the evaporator in one place, i imagine it has for years without any problem, but i've re-done the routing so they can't touch anymore, no change.
i have tried:
- Install LED on + & D terminals (no errors indicated)
- Jumper past the thermostat using C & T terminals (appears to run fine by taking the thermostat out of the loop) - it'll run and run and run without shutting off
- disconnecting the fan (no change if the thermostat is connected but the fan isn't - still cycles)
- running on shorepower - no change
- connecting the sense tube directly to the evaporator instead of to the plastic back of the "o" shaped evaporator - no change
- made sure the sense tube can't touch an evaporator line before it touches the evaporator - no change
Thank you all very much for any help