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Old 14-03-2018, 20:52   #1
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Isotherm CR165 Compressor Fridge

Hi to All.
I’m another newby to this forum.

Having a problem with my new Isotherm CR165 compressor fridge that I would appreciate some guidance with.

Because of the problems I had with my previous fridge I decided to test this one out of the box before installing it.

The issue I am having is that the compressor runs continuously if the ambient temperature is above 28C.
The “box temperature” continues to decrease while the compressor runs.
If it continues long enough, it will start to freeze the box contents.
The compressor will turn off only after the ambient returns to 28C, regardless of how low the box temp gets.

I note also that the thermostat differential seems to vary depending on ambient temperature. With the thermostat set to 4.75, the compressor “turn on” point remains constant at 5C while the “turn off” point decreases with an increase in ambient.

This fridge has condensers as part of the side walls as well as a separate small, fan assisted radiator next to the BD50.
The thermostat is located in a recess on the internal side wall behind the fridge light. A capillary tube extends from the thermostat, inside the fridge wall to make contact with the evaporator at the rear. I’m using Elitech RC-5 loggers for the temperature measurements.

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Hoping someone can explain why I’m seeing what I’m seeing.
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Old 15-03-2018, 01:24   #2
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Re: Isotherm CR165 Compressor Fridge

I do not see the typical ASU normally used by Isotherm to increase compressor speed. I believe compressor speed is too low for that ambient high temperature.

Compressor appears to be running always at minimum 2000 rpm speed. By adding a resistor in thermostat wire you can compensate for high ambient temperatures. See Slide Show on my web site for compressor speed resistor at Kollmann Marine.
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Old 15-03-2018, 02:59   #3
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Re: Isotherm CR165 Compressor Fridge

Quote:
Originally Posted by Richard Kollmann View Post
I do not see the typical ASU normally used by Isotherm to increase compressor speed. I believe compressor speed is too low for that ambient high temperature.



Compressor appears to be running always at minimum 2000 rpm speed. By adding a resistor in thermostat wire you can compensate for high ambient temperatures. See Slide Show on my web site for compressor speed resistor at Kollmann Marine.


Hello Richard,

thank you for the link to your web site. I’m on a steep learning curve so all that information will be very useful.
I checked and there is actually a resistor in the in the thermostat wire.
It measures 1488 ohms. Looks to be a .25 watt and is hidden under shrink wrap.
Of the 5 or so separate tests done, with one up to ambient of 41C,
I consistently see that the compressor will only turn off when the ambient reduces to 28C. What puzzles me is why 28?

The other question mark I have is the aparent drift of the thermostat differential with ambient increase. Would this be typical with this type of thermostat?
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Old 15-03-2018, 06:35   #4
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Re: Isotherm CR165 Compressor Fridge

There is a wire connected to P terminal in picture the battery's low voltage protection resistor terminal. The 1488 ohm resistor installed in wire to T terminal will run compressor at 3500 max Rpm producing amperage above 5.5.

Are you sure that each wire does not have a resistors and they are on the correct terminals?
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Old 15-03-2018, 09:04   #5
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Re: Isotherm CR165 Compressor Fridge

Hello,
In your case I´d ask all my questions to the producer, I´m sure you will receive the correct answer.
https://www.indelwebastomarine.com/int/

Regars
Rolly
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Old 15-03-2018, 12:45   #6
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Re: Isotherm CR165 Compressor Fridge

The answer to question why compressor reaches an equilibrium at ambient temperature of 28 degrees C is because compressor's Btu output is close to the Btu heat load for that size insulated box. A major improvement will happen when compressor Btu output is increased. Amperage of 4.2 amps confirms very low output from compressor.

If you want to confirm compressor preset speed open refrigerator circuit breaker. Set thermostat to full cold. Disconnect wires from module terminals C and T and using an ohmmeter check the resistance of thermostat and wiring with meter between the two wires. No resistance compressor will run at 2,000 Rpm, Increase resistance with a 1,488 ohm resister compressor will run at 3,500 Rpm.
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Old 15-03-2018, 15:46   #7
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Re: Isotherm CR165 Compressor Fridge

Hi RV, Speeding up your compressor will NOT resolve this problem it will make it worse! Your data log charts and pictures of that refrigeration unit tell the story.
Assuming that being a new mass produced fridge the gas charge is correct, that air cooled system is grossly under condensed. Therefore as the ambient increases the refrigeration unit is unable to reach the thermostats cut out temperature, (at the thermostats sensor where it reads the last of the evaporator line, not cabinet temp.) Your data logger confirms this.

If you could log the temperature exactly as the fridge thermostat does you would see that while thermostat cut off temp is reached in moderate conditions it is not reached in the higher ambient causing the unit to run on lowering the cabinet temperature excessively.
Increasing the compressor speed will only make your problem worse.

Again assuming the gas charge is correct, (and I suspect it may not be!) the best remedy is to improve the systems condensing ability but to do that properly would mean replacing that tiny air cooled condenser with a properly sized one. An easier fix that may work would be to increase air across the existing condenser by fitting a stronger fan. The fan now is a most likely a 120 - 120- 25 and you could replace with a higher wattage one or if space allows go to a 120 - 120 - 37 but make sure the fan is less than 5.5 watts.
And an easier yet suggestion is to move the thermostats sensor back towards where the refrigerant flow comes from. To identify this, view the sensor area when the problem is occurring and move to the frosted part of the pipe.

BTW, looking at your pictures makes me shudder as a refrigeration engineer! Not only is that condenser grossly undersized but the discharge pipe runs virtually straight from the compressor (which moves slightly) to the condenser. A recipe for a broken pipe in the future, so if you get a decent condenser fitted make sure there is allowance for movement in that pipe run. In my opinion that cheap cabinet and refrigeration system set up is terrible.

Cheers, OzePete Ozefridge | 12 Volt Refrigeration Systems
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Old 15-03-2018, 16:07   #8
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Re: Isotherm CR165 Compressor Fridge

Man, listening to you guys talk is like listening to guys talk about rocket science....Thank Goodness there are guys like RK and Oze who do this for a living.
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Old 15-03-2018, 16:39   #9
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Re: Isotherm CR165 Compressor Fridge

Pete, you have really out done yourself this time, attacking Isotherm a competitors engineering in an effort to sell your product.
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Old 15-03-2018, 18:05   #10
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Re: Isotherm CR165 Compressor Fridge

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Originally Posted by Richard Kollmann View Post
Pete, you have really out done yourself this time, attacking Isotherm a competitors engineering in an effort to sell your product.

Richard yet again you ‘jump ship’ to avoid discussing the actual topic at hand. It is also almost comical as to how quickly the subject is diverted whenever I correct blatantly wrong information.
You say the opinion I expressed regards that poorly built refrigerator / system was an attempt to sell my product? We have never ever built Ozefridge refrigerators, we only build refrigeration systems!
I will never avoid pointing out issues or blatantly incorrect refrigeration information from who-ever especially when correction is needed to help users resolve or avoid problems.
You say I attacked a competitors engineering! Richard, have you looked at the photos supplied? Surely you can identify the issues from the pictures that should be obvious to any refrigeration engineer.
To help you out let’s list what I believe should be pointed out to potential users / buyers of such products:
1. The condenser is grossly undersized. This means that disposing of heat from the system is limited especially on hotter days.
2. The discharge pipe from the compressor to the condenser is virtually straight offering no relief from movement. This is something any refrigeration person knows not to do as that pipe is very likely to crack and lose all refrigerant followed by system contamination. All to save a few cents by having a longer looped pipe!
3. The suction line pipe is connected to the ‘Process coupling’ on the Secop compressor and the process valve is connected to the ‘Suction coupling! (See Danfoss / Secop manual)
4. The use of a cheap spun copper so called filter dryer which is really a strainer dryer as they have no felt filter at all! Should use a 032 true ‘Filter dryer’.
5. The use of ‘paper for wall linings!! Etc etc...
So Rich for a simple fridge you surely would agree with my opinion that it is very poorly built item.

Cheers, Ozepete Ozefridge | 12 Volt Refrigeration Systems
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Old 15-03-2018, 18:12   #11
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Re: Isotherm CR165 Compressor Fridge

Quote:
Originally Posted by Richard Kollmann View Post
There is a wire connected to P terminal in picture the battery's low voltage protection resistor terminal. The 1488 ohm resistor installed in wire to T terminal will run compressor at 3500 max Rpm producing amperage above 5.5.

Are you sure that each wire does not have a resistors and they are on the correct terminals?
Here is a better pic of the terminations
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That red heatshrink on terminal T conceals the resistor. I can confirm that when I remove the wires from C and T and measure back thru the thermostat contacts I am reading 1488 ohms
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Old 15-03-2018, 19:11   #12
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Re: Isotherm CR165 Compressor Fridge

Quote:
Originally Posted by OzePete View Post
Refrigeration Systems[/url]
Hi OzePete,

thanks for looking at this.

Quote:
Originally Posted by OzePete View Post
that air cooled system is grossly under condensed
The side walls of the cabinet are also condensers but I have no idea how effective they are. I guess its still undersized taking them into account?

With the question mark over the gas pressure, would it be advisble to get that checked first?

I can certainly buy a higer volume fan for sure.

With regards to moving the sensor, I'll check it out but I dont think I can gain access to that point. The capillary tube just disappears into the sidewall of the cabinet and the sensor area and pipe seems to be embedded somewhere in the isulation ( I think).

With regards to the build quality, I must admit I had some concerns. Its not obvious from the photos but the radiator is not actually secured to the chassis. Its only supported by the copper piping at one at one end and a few cable ties. I can wriggle it without much effort. One of the compressor mounting nuts is also missing. The thing is I'm stuck with this fridge cabinet because its not possible to modify the cabinetry in the caravan for an alternative.

Neal
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Old 15-03-2018, 19:43   #13
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Re: Isotherm CR165 Compressor Fridge

Ok OzePete,

re read your post again about moving the sensor. If it's not accessable, as I think, would it be a viable alternative to replace the existing thermostat with a digital one that monitors the internal cabinet temperature?

I don't know what the downside, if any, would be.

Given that the cabinet temp will actually reduce to the desired level, even when the ambient is very high, it seems to me that the object of the exercise is achieved?

Neal
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Old 15-03-2018, 19:44   #14
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Re: Isotherm CR165 Compressor Fridge

Quote:
Originally Posted by rvlandlubber View Post
Hi OzePete,

thanks for looking at this.


The side walls of the cabinet are also condensers but I have no idea how effective they are. I guess its still undersized taking them into account?

With the question mark over the gas pressure, would it be advisble to get that checked first?

I can certainly buy a higer volume fan for sure.

With regards to moving the sensor, I'll check it out but I dont think I can gain access to that point. The capillary tube just disappears into the sidewall of the cabinet and the sensor area and pipe seems to be embedded somewhere in the isulation ( I think).

With regards to the build quality, I must admit I had some concerns. Its not obvious from the photos but the radiator is not actually secured to the chassis. Its only supported by the copper piping at one at one end and a few cable ties. I can wriggle it without much effort. One of the compressor mounting nuts is also missing. The thing is I'm stuck with this fridge cabinet because its not possible to modify the cabinetry in the caravan for an alternative.

Neal
Hi Neal, shocked that the condenser (radiator) is virtually relying on the discharge pipe and cable ties!! You may be able to fit a mount under it and use non acetic silicon to 'bed' it down. A silicon bed will at least allow it to flex with any compressor movement! The incorrect fitting of the suction and process pipes I mentioned is not a big issue and will not effect anything.

The suggestion of relocating the sensor probe is because where it is it is effected by a reduction in refrigeration when the ambient increases. It is located near the end of the evaporator pipe run and needs to be a little earlier so that the reduction of ability to refrigerate all the evaporator to where the sensor is now, will not cause it to sense warming and keep the compressor running.

I mentioned the possibility of gas shortage because when a system is short the first indication is that the amount of evaporator pipe run to get refrigerated is reduced and that reduced area is where your temp robe is.
If it is possible you might get a fridgie to add a 'sniff' of gas to extend the freeze run and possibly resolve the problem, but watch to make sure it doesn't freeze back to the compressor (too much gas)

Good luck with that.

Cheers, OzePete
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Old 15-03-2018, 19:56   #15
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Re: Isotherm CR165 Compressor Fridge

Quote:
Originally Posted by rvlandlubber View Post
Ok OzePete,

re read your post again about moving the sensor. If it's not accessable, as I think, would it be a viable alternative to replace the existing thermostat with a digital one that monitors the internal cabinet temperature?

I don't know what the downside, if any, would be.

Given that the cabinet temp will actually reduce to the desired level, even when the ambient is very high, it seems to me that the object of the exercise is achieved?

Neal
Hi Neal,
Absolutely that would be an ideal solution and you will have a constant temperature read out to monitor the fridge along with programmable cut in and cut out settings. Suggest a 12 VDC STC8000 from Elitech (Buy on Ebay about 20.00
Best solution so far.... now why didn't I think of that!

I don't suppose you need a job Neal!

Cheers OzePete
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