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Old 22-12-2018, 22:21   #1
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Fridge is cooling, but less than before....

So last week our water cooled Isotherm fridge started dripping water. I figured it was just the seals on the water pump going bad, as they all seem to do after about a year and a half. When I pulled things apart it became apparent that the leak was coming from the condenser coil/ water jacket. The hose barb for the condenser coil had corroded away and there wasn't enough left to make a good connection. In researching options to fix it, a local refrigeration shop suggested switching over to an air cooled system. They said they had a larger than normal condenser that still would work fine in the tropics (we're currently in Phuket). This seemed like a good idea, as the water cooled system is always needing attention to unblock lines, de-calcify the condenser coil, swap out pumps, etc. So we went ahead and made the switch.

The new system utilizes the same compressor and control unit (BD 50 compressor) and replaced the water cooling with a fan cooled fin-type condenser. The unit is cooling, but not as well as before. The evaporator plates are at about 12-16 degrees F (not certain what they were before), and this is just holding the box around 34 degrees, but the unit runs constantly. Previously the unit could easily freeze the box and had about a 50% cycle rate. The capillary tube side of the system is pretty warm to the touch, even after it comes out of the condenser. The unit is mounted below the floor, but it has pretty good ventilation. Taking a temperature reading of the surface just in front of the fan intake shows about 90 degrees, which is just a couple of degrees above the ambient temp, so I think the compartment is getting adequate ventilation. The complete system (fan + compressor) is pulling 5.3 amps at 12.8 V. I'm wondering if this is a case of:
  • Not having a large enough condenser unit or,
  • Perhaps the unit may be slightly undercharged (they vacuumed the system out and refilled it) or,
  • Something else happened during the install when they brazed the parts together.

Any thoughts on why the system is not cooling as well as before?

Cheers- Matt
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Old 22-12-2018, 22:26   #2
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Re: Fridge is cooling, but less than before....

Water cooled systems , perform far better than aid cooled .
Probably the system can't extract the heat .
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Old 22-12-2018, 22:40   #3
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Re: Fridge is cooling, but less than before....

Quote:
Originally Posted by teneicm View Post
So last week our water cooled Isotherm fridge started dripping water. I figured it was just the seals on the water pump going bad, as they all seem to do after about a year and a half. When I pulled things apart it became apparent that the leak was coming from the condenser coil/ water jacket. The hose barb for the condenser coil had corroded away and there wasn't enough left to make a good connection. In researching options to fix it, a local refrigeration shop suggested switching over to an air cooled system. They said they had a larger than normal condenser that still would work fine in the tropics (we're currently in Phuket). This seemed like a good idea, as the water cooled system is always needing attention to unblock lines, de-calcify the condenser coil, swap out pumps, etc. So we went ahead and made the switch.

The new system utilizes the same compressor and control unit (BD 50 compressor) and replaced the water cooling with a fan cooled fin-type condenser. The unit is cooling, but not as well as before. The evaporator plates are at about 12-16 degrees F (not certain what they were before), and this is just holding the box around 34 degrees, but the unit runs constantly. Previously the unit could easily freeze the box and had about a 50% cycle rate. The capillary tube side of the system is pretty warm to the touch, even after it comes out of the condenser. The unit is mounted below the floor, but it has pretty good ventilation. Taking a temperature reading of the surface just in front of the fan intake shows about 90 degrees, which is just a couple of degrees above the ambient temp, so I think the compartment is getting adequate ventilation. The complete system (fan + compressor) is pulling 5.3 amps at 12.8 V. I'm wondering if this is a case of:
  • Not having a large enough condenser unit or,
  • Perhaps the unit may be slightly undercharged (they vacuumed the system out and refilled it) or,
  • Something else happened during the install when they brazed the parts together.

Any thoughts on why the system is not cooling as well as before?

Cheers- Matt
Hi Matt, a few things to check:
1: Are the evaporator plates refrigerating completely top to bottom? If only partly it may be low on refrigerant.

2: Is the suction line (pipe from evaporator to compressor) sweating or frosting? If yes there is too much gas in the system. (I suspect this as most likely the problem)

3: What is the size of the new condenser (Fin area width x height x number of coil passes) and fan model?

4: Your new condenser has a pipe with hot refrigerant gas from the compressor entering at the top and warm liquid refrigerant pipe leaving at the bottom.
The bottom pipe should be approx 8C warmer than the ambient so wrap your hand around that pipe and it should be slightly warmer than body temp if all else is correct and the condenser is effective.

Response to the above will be a good start to diagnosis of your problem.
If possible a picture of the new condenser / fan would help!

Cheers OzePete
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Old 22-12-2018, 22:59   #4
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Re: Fridge is cooling, but less than before....

Quote:
Originally Posted by OzePete View Post
Hi Matt, a few things to check:
1: Are the evaporator plates refrigerating completely top to bottom? If only partly it may be low on refrigerant.

2: Is the suction line (pipe from evaporator to compressor) sweating or frosting? If yes there is too much gas in the system. (I suspect this as most likely the problem)

3: What is the size of the new condenser (Fin area width x height x number of coil passes) and fan model?

4: Your new condenser has a pipe with hot refrigerant gas from the compressor entering at the top and warm liquid refrigerant pipe leaving at the bottom.
The bottom pipe should be approx 8C warmer than the ambient so wrap your hand around that pipe and it should be slightly warmer than body temp if all else is correct and the condenser is effective.

Response to the above will be a good start to diagnosis of your problem.
If possible a picture of the new condenser / fan would help!

Cheers OzePete
Thanks for the reply Pete. Still owe you a beer for helping with the freezer about a year ago!

OK, here we go:

1) Plate seems to be cooling uniformly. There is frost over the entire plate and the temperature variations between different areas on the plate are less than 5 degrees F.

2) Hard to see, as this line is wrapped in several layers of insulation, but it does appear that there is some ice just at the point where the suction line leaves the box.

3) Condenser area is 15cm x 13 cm and there are 8 passes through the condenser.

4) The pipe you are talking about is the one that connects to the capillary line, correct? If so, that pipe is quite a bit above ambient: roughly 125 to 130 degrees (hard to get a good reading with the IR gun).

So the capillary line should be quite a bit cooler, right? Sounds like the condenser isn't getting the job done?

Cheers- Matt
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Old 22-12-2018, 23:10   #5
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Re: Fridge is cooling, but less than before....

Click image for larger version

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Hard to get a good shot....
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Old 22-12-2018, 23:18   #6
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Re: Fridge is cooling, but less than before....

Cheers Matt,
That condenser is the problem, it is far too small specially for use in the tropics. If stuck with this inefficient condenser you may help it if you replace the 120-120-25 fan with a 120-120-38 but if you do change it the stronger fan needs to be less than 6 watts otherwise power it via a relay.

Cheers OzePete
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Old 22-12-2018, 23:23   #7
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Re: Fridge is cooling, but less than before....

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Originally Posted by OzePete View Post
Cheers Matt,
That condenser is the problem, it is far too small specially for use in the tropics. If stuck with this inefficient condenser you may it if you replace the 120-120-25 fan with a 120-120-38 but if you do change it the stronger fan needs to be less than 6 watts otherwise power it via a relay.

Cheers OzePete
So the black box can handle up to 6 watts? What size condenser should I be looking for? Kinda annoyed as I specifically addressed this issue and was told that it would be sized appropriately... At least I'm not stuck in the backwoods this time!
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Old 23-12-2018, 00:50   #8
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Re: Fridge is cooling, but less than before....

Here is the condenser we used for BD50 systems for tropical use:

Click image for larger version

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ID:	182657

Cheers OzePete
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Old 23-12-2018, 01:32   #9
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Re: Fridge is cooling, but less than before....

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Originally Posted by teneicm View Post
So the black box can handle up to 6 watts? What size condenser should I be looking for? Kinda annoyed as I specifically addressed this issue and was told that it would be sized appropriately... At least I'm not stuck in the backwoods this time!
I wonder what they will say if you go back and tell them the issue .
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Old 23-12-2018, 09:59   #10
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Re: Fridge is cooling, but less than before....

I too got tired of servicing the Isotherm water cooled units, switched to Cold-Eh system (Canadian), much more efficient, a lot less current draw and no filters.....one Danforth 50 for the refrigerator and two 35s for the freezer
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Old 23-12-2018, 18:15   #11
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Re: Fridge is cooling, but less than before....

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I wonder what they will say if you go back and tell them the issue .

Yep, me too... waiting for a reply but it'll be a few days as they are closed for the holidays. They were very good to work with initially, so I'm hoping for a good outcome. The major pain is that they will only work in marinas and all the local marinas are filled up at the moment.
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Old 23-12-2018, 23:01   #12
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Re: Fridge is cooling, but less than before....

Just eaves dropping all the above.
Aren't Isotherm eutectic?
I thought one would use eutectic when there is a large capacity compressor.
Wouldn't a 50W compressor would run more efficiently with a cold plate?
I can't see the point of running a small compressor 50W for hours trying to make ice in a eutectic plate. There's no really a hold over because the compressor never seems to stop in most that I've seen or heard about.
Another opinion / point of view would be excellent while we are on the subject.

Cheers.
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Old 24-12-2018, 07:17   #13
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Re: Fridge is cooling, but less than before....

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Originally Posted by MIRELOS View Post
I too got tired of servicing the Isotherm water cooled units, switched to Cold-Eh system (Canadian), much more efficient, a lot less current draw and no filters.....one Danforth 50 for the refrigerator and two 35s for the freezer

Thanks Carlos.

We designed the system to be strictly air cooled in all climates .

This picture shows the size of our condenser with twin fans. All 1/4" tubing .

Regards John.
Merry Christmas everyone.
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