View Full Version : AC Jr temperature freaking out

05/26/2007, 01:57 AM
I have my AC Jr set up to cool the tank with a fan when the tank gets too warm and the heater to come on when the tank gets too cool.

It has worked wonderfully for the year that I have had the unit.

Until tonight. My fan is staying on and the temperature is jumping up and down on the unit like crazy. It says that the tank is in the low 90's but there is no way. It is changing temps constantly.

Does anyone know what is going on and how I can fix it?

update. It now says my tank is 106 degrees F!!!!!
I even took the temp sensor out of the water and it still says this :eek2:

It is about 70 up here in this room if that.

05/26/2007, 03:36 PM
This is most likly a failed tempature probe.
I have had 2 of them... and they seem to always fail HI and the chiller keeps running and it is a mess..


if you unplug the probe from the unit it The AC should read aproamatly 20 deg F... ( at least on the AC3 I dont have ACjr should be simular)

This will vary a little due to the temp calibration...

good luck and always have a analog thermomiter in your tank ...

I bought an expansion module to add a 2nd temp prob just because of this .. ( and I have a glass therm. in the tank also)

Roy G. Biv
05/26/2007, 04:15 PM
It's funny how people always recommend an external temerature controller instead of a heater because it might fail and stay on cooking your tank, but many people here say these probes fail, seems like more frequently than heaters.

05/26/2007, 05:13 PM
I think Fail safe is the key here!

have a heater with therastat plugged in to your controller...
that way if something fails then you are better off ..

05/26/2007, 05:42 PM
this is the first I have heard of these things failing. I am really disappointed as this thing didn't even last a year. Lame.

I now feel that I can no longer trust this expensive piece of equipment.

I would like a response from neptune. My cheap $10 coralife thermometer still works 3 years later so what gives?

up until now I thought this was the single best investment I have made. Now I feel like it is a disaster waiting to happen and it would have been if I would not have been here to catch it.

I don't understand what it is that could cause these things to go bad.

05/26/2007, 10:26 PM
oh I agree ... I was completely freaked that this happened..

I am where you are with the reliability..

all Curt would tell me is there must be some trauma to the probe to cause it to fail

My probes are stationary in the sump ... no trauma un less it happened in shipping ...

And I had 2 fail I had to buy the 1st one and then the replacement failed in less then 2 months. and Curt replaced it ...

the 2nd one contribuited to a pipe fish to dieing ( it was new to the tank and stressed anyway)

after the 1st one I lost a coral cant be sure of the cause of that except the stress of the temp plumiting couldnt help matters

so I understand your frustration

05/27/2007, 01:43 AM
Weird... Going on three years with the some probes, pH and temp, that came with my jr. Not a single problem, just calibrate the pH probe every 6 months or so...

At least you got a good answer CeeGee! Much better than my guestimate last night:lol:

05/27/2007, 02:40 AM
No trauma here either. Unless it occurred on the chinese assembly line where I am sure this was made.

I am so sick of buying stuff that breaks.

05/29/2007, 01:16 PM
Clean the temp probe. worked for me. Mine freaked out after about 8 months as well. soaked in some vinegar/water, took a toothbrush to it for a second and plugged it back in and worked fine. Now I add it to my quarterly cleaning schedule.

05/29/2007, 04:29 PM
Will try that. I ordered another from premium aquatics.

Thanks for the tip Dr. Evil!

05/29/2007, 08:07 PM
Mine did the same a while back. I ended up buying a replacement from Kurt. Make sure you buy the temp probe for the ACjr if its the jr, they are different I believe.

05/30/2007, 07:56 PM
Thank you to everyone who helped me out since 5 days later and no response from neptune.

New probe should be here in the next day or two and in the meantime I am going to clean the one I have now.

05/31/2007, 08:29 AM
Cleaning the current probe did absolutely no good. Just as I figured I have a piece of equipment that failed in less than a years time. Seems to me that someone needs to check into the quality of these probes. I can understand a ph probe going bad as it is a known fact that they need to be replaced but a temp probe? come on!

as a matter of fact my pH probe is still functioning normally. It should be the other way around. I guess on the bright side the temp probe is cheaper than the pH probe. Although I am sure the pH will be failing here shortly.

David Grigor
06/01/2007, 05:09 PM
Best to keep the temp probe cord totally away from any other power cords etc. any excess temp probe length should be neatly looped ( about the same size loops as it comes packaged ) and secured. If your anything like me, the power cords can get to be a tangled mess. You pull on one and it tangles together can crimp the temp probe.

Also, if you have any lids on your sump or any sharp edges ( arcylic ) corners can be sharp unless your filed them down or rounded the ends with a router. Any occasional rub from moving equipment, lids etc. can slowly cause wear. It can be such that even days/weeks after you do the damage that it causes an issue so don't just assume that since you didn't touch it today that it wasn't already damaged. Rarely will you see any physical marks or damage to the wire as it can happen inside the insulation.

Do these things and you shouldn't have an issue. I had one fail before I knew how careful you should treat it.

I would like to see more heavy duty insulation around the wire but with care you will be fine.

Lastly, since when they fail usually with very high temp readings, you can program to turn off the fans when temp is > 100 since that will most likely be in error. Set up an audible alarm as well. So at least your fans won't keep cooling the water making matter worse as it did in my case. Of course your heater won't cut on either but better then nothing.

06/01/2007, 07:01 PM
Lastly, since when they fail usually with very high temp readings, you can program to turn off the fans when temp is > 100 since that will most likely be in error. Set up an audible alarm as well. So at least your fans won't keep cooling the water making matter worse as it did in my case. Of course your heater won't cut on either but better then nothing.

I had actually done this..

however the rest of what you say is valid, ( dont cut the wire etc.)
but these are not failing due to any trauma of any sort.

I am well aware of how to care for this stuff and short of wrapping the probe in stirophome insulitaion I dont know what can be done to make the probe safer.

I ended up purchasing a spare to have on hand.

this along with the expansion module And the code mentioned above ( if Temp >90 then Chiller OFF ( at 90 everything is toasted anyway ) I also added a supper low fail safe figuring there is no way tha tthe tank would still be alive at 60 deg so HET off

06/01/2007, 07:59 PM
cee ce I am in Knox and I have the jr 3 and it has been great for me and curt has always taken good care of me hope all works out for you

06/01/2007, 10:52 PM
hawkeye haven't heard a word from old curt ;)

Why am I not surprised? It seems like nothing is going my way these days. I ordered the new probe from premium aquatics on tuesday should have been here at the latest today. Never got a confirmation email or a tracking number. It hasn't shown up :rolleyes: My bank account has been charged though :rolleyes: sent a email this morning to them and guess what? Never heard back from them :rolleyes:

have you met fishdoc11 yet? Super cool guy and has some good frags every now and again ;)

David G,

I installed both probes very carefully and haven't touched them since. Haven't had to. Thank you for your input though maybe it will help others. Also thank you for taking the time to try and help me out.

06/02/2007, 12:34 PM
FWIW- My Jr temperature probe worked great for 3 months or so. Then the temperture started to jumppretty fast +-2 degrees. I moved the temperature probe to the other side of the tank away from the pumps and it stared working fine again. I have no clue why it worked fine for months without any chages and then started acting up. It's still working fine after the move. Very strange.