domestic frost free control methods

hello , im building my own control board for a whirlpool american style fridge freezer using arduino , i wasnt sure if i should post here or in the domestics section seeing as its quite technical

i just wanted to run it by someone how this thing actually operates so i can get the coding right

my understanding is so

- read freezer temp , if temp ok do nothing if temp above preset amount start compressor and evaporator fan and condensor fan -

- when freezer down to temp shut off compressor and leave evaporator and condensor fans running for a couple more mins - 15 or so?


as for fridge - check temp - if above preset open baffle and start evaporator fan

if below close baffle stop evaporator fan


if fridge door opens close baffle to stop wastage
if freezer door opens stop evap fan

if doors open for long period shut off compressor and alarm



i have a few questions

- whats the method to start compressor , i realise there is a ground and two lives and a cap.. is it a soft start option? you start up on one live and switch to the other after a few seconds?

how frequently can the compressor be cycled - ie how long between stop and restart - plus how long can it run for without a rest

is there ever a situation where compressor is running without evap fan? and why




i didnt get to the defrost code yet but i realise something will have to be done

Rickbu. When freezer at temp, leave evap. fan running. 2. fridge baffle is either electric or manual. Easier to set it manually...3, fridge or freezer door opens, turn off evap. fan. Some manufacturers turn off evaporator fans when at temperature but i like constant air flow. Evap fan only switches off when in defrost and should not turn back on untill fan delay thermostat reaches temperature... 4. Capacitor is to help start compressor, CSIR. No softstart available that i know of, YET, Relay on compressor does the job. Appliance runs as required so could run a few hours initially to get temperature and could cycle, say 4 times/hr, sometimes more. 5. Compressor will run without evap fan after defrost(as above) and when either door is opened.. Mike.

Hello mikeref and thanks for your reply , ive finally got all the hardware hooked in and the software side of this project all done , the front display panel of the fridge has been replaced with a blue backlit lcd and everything is up and running and under control including the ice maker and the water dispensor but now i have a few questions in order to just tweak the software to perfection

what kind of hysterisis should i be looking at on the freezer .. i understand its not good to have the compressor cycling often correct?

how often should i start the defrost cycle.. i read that some fridges use a timer and some do it on a door open and close count , which system do you believe to be the best as i can implement both ( i am monitoring door open signals as well as run times in the software ) and how long should the defrost cycle run for - just until the defrost thermostat cuts off?

one other thing , i think the refrigerant in the unit may be low lucky for me the unit is already fitted with a brazed on service valve( it must have been serviced at some point in its life) . can i top it up using the automotive r134a cans available? it seems they have the same fitting .

the reason i suspect low refrigerant is it seems to take a long time to get down to temp - although it Does get to temp. but while the compressor is running every 15 seconds or so i can hear it sucking air - i think , like when an aerosol can is running out and starts just spraying gas and not liquid and its my understanding that the compressor should be pumping liquid gas am i right? and my other samsung freezer seems to drop temperature much faster than this . although it is a smaller unit to be fair.




anyway its getting late and im sure i forgot to mention something but thanks for your help so far mikeref

Rick

Rick, Defrost is usually every 6 hours for around 21 mins. Defrost termination thermostat or probe is in current position so if freezer coil defrosts prior to that time, then heater power is terminated and fridge waits it out for the 21 mins before cooling cycle resumes. Now this proceedure is not written in stone these days as some fridges use more powerful heaters and defrost can be done in as little as 10 mins every 8 hours so you'll have to go back and find out this fridge specs on defrost.... fridge might cycle 3 times/hour on thermostat, depending on load/door openings and ambient temps....and before you tinker with gas charge, check suction line temp to compressor when freezer is down to -18c. Line should be cool only, not frosted or warm when compressor is running. No liquid refrigerant will be pumped if you do not add gas, and the noise is liquid/vapour exiting the capillary tube and going into evaporator to boil off...Mike.