Isotherm Fridge Problem - no green

[Tintin]

The new (to me) Beneteau 325 has an Isotherm 3000/3500 fridge, circa mid 90's.

On battery power I can switch the ASU (the old type - 3 LED's and a switch) between On and Freeze, but on "On" no green LED comes on, only the yellow "economy" LED, the fan does not run, but the compressor does seem to run and the fridge gets cold'ish. But it sucks about 5 amps continuous. If I switch to Freeze the red freeze LED comes on, the fan comes on, and the compressor runs (but no noticeable noise increase which I would expect with it supposed to be running at a higher rate, and eventually (after several hours) the collector plate gets to a level of cold that I would expect.

When the engine is charging the batteries and I have 13.8v+ knocking around it does exactly the same in both modes. I believe what should happen is that in "on" and at that voltage I should see a green light and the compressor should kick in with the fan, with the compressor running at high speed until the fridge gets down to a low temp, when it should switch into economy mode (low compressor speed and no fan).

Any idea what may be broken?

 

[corinthmistral]

I had a similar(ish) problem with my isotherm fridge and the problem was with the three way switch. When in auto or freeze mode one of the lights came on but the unit didn't run properly. I eventually discovered that when I held the switch on it worked ok and it had a dodgy connection. I removed the face plate housing the switched, hosed it in wd40, worked the switch on and off lots of times and it's worked fine ever since. A bit of a long shot but might be worth trying that to start with.

 

[john_q]

My 2 pennies worth

Do not jump the gun and spend a fortune on Isotherm parts

After many years of paying Isotherm’s ridiculously high prices for spares. I now have what I guess you would call an Isotherm Hybrid

The unit started life as Isotherm 4200 ASU water cooled unit. Long story short, current configuration is as follows:

• Removed Isotherm electronics unit ($350) from the Danfoss BD50 compressor,
• Bypassed the Isotherm 3 way switch,
• Rewired as per the non ASU model
• Fitted a separate thermostat control ($10)

Unit now only runs at low speed (but this could be changed) and draws 3 amp, comes on 6 times a day for 2 hours a time and this is in the tropics. It has been working like this since 2011

Good luck

 

[Chris_Robb]

When the engine is charging the batteries and I have 13.8v+ knocking around it does exactly the same in both modes. I believe what should happen is that in "on" and at that voltage I should see a green light and the compressor should kick in with the fan, with the compressor running at high speed until the fridge gets down to a low temp, when it should switch into economy mode (low compressor speed and no fan).

Any idea what may be broken?

No idea on the fridge, but your battery voltage at 13.8 is far too low whilst the engine is charging, you should be seeing 14.4 to 14.8V or otherwise your batteries are seriously flat and perhaps the low voltage circuitry is stopping the fridge working. What ever the problem on the fridge, you really should be seeing at least 14.4V on a reasonably charged battery.

 

[Tintin]

No idea on the fridge, but your battery voltage at 13.8 is far too low whilst the engine is charging, you should be seeing 14.4 to 14.8V or otherwise your batteries are seriously flat and perhaps the low voltage circuitry is stopping the fridge working. What ever the problem on the fridge, you really should be seeing at least 14.4V on a reasonably charged battery.

Errr, no. I dont want to turn this into a battery voltage discussion but13.8v (and note i wrote 13.8v plus sign) is a normal float charge voltage. 14.6v is about the safe max for the bulk charge phase with bog standard lead acid batteries and without a smart or external regulator most will only see 14.2v for a brief time at the start of charging with a normal alternator.

If your "reasonably charged" batteries are showing 14.8v you either have a problem or a faulty voltmeter.

The fridge low voltage circuit (danfoss standard) cuts out at something like 10.5v and back in at 11.7 (i dont have the exact spec to hand).

Sorry for correcting you re: voltages but someone may have read it and wondered why their batteries were "only" reading 13.8v.

 

[john_q]

Do you have the manual for the unit?

My manual for a 4201 which is a BD50 water cooled unit but I think uses the same type of switch says the following about the lights (if you do not have a manual but want a PDF file of my one, drop me a PM)

Indicator lights

Green
Power and system on, the compressor is stand-still due to sufficiently low temperature of the holding plate.

Green + yellow
Compressor running within the higher temperature range.

Green + red
Compressor running within the lower temperature range.

Green + yellow + red
Compressor running at lowest possible speed to reach selected temperature in MAN.TEMP working mode.

Flashing yellow + red
Error signal from the electronic unit. Automatic re-start after 1 minute.

Flashing yellow
Low battery voltage sensor has stopped the compressor. Automatic re-start occurs when engine is started to charge batteries again.

I wonder if the Green bulb has blown?

 

[Chris_Robb]

Errr, no. I dont want to turn this into a battery voltage discussion but13.8v (and note i wrote 13.8v plus sign) is a normal float charge voltage. 14.6v is about the safe max for the bulk charge phase with bog standard lead acid batteries and without a smart or external regulator most will only see 14.2v for a brief time at the start of charging with a normal alternator.

If your "reasonably charged" batteries are showing 14.8v you either have a problem or a faulty voltmeter.

The fridge low voltage circuit (danfoss standard) cuts out at something like 10.5v and back in at 11.7 (i dont have the exact spec to hand).

Sorry for correcting you re: voltages but someone may have read it and wondered why their batteries were "only" reading 13.8v.

Ok - I missed the + but even then the alternator only goes to float charge (if its clever enough to do so) after a considerable time. I made an assumption that this was normal running volts.

I did not say 14.8 for a reasonably charged battery, I said 14.4V. And where did you get the idea that batteries cannot be charged to 14.8V, Provided they are the right batteries of course you can. If you want to read E-nex recommendations you can - and they are sealed batteries. So no I don't have a faulty volt meter.

If people are only seeing 13.8 at their batteries then they do have - not necessarily a problem, but a very slow charge rate indeed. So they should take note.