Fridge evaporator plate has no frosting after coolant recharge

[claptrap]

Our fridge had only partial frosting on the evaporator plate for a few weeks (so low on coolant).
I've recharged it and now, the evaporator plate does not show any frosting (even after one night of running) and sits at about 10C.

Did I overcharge?

The pressurized hose is warm to the touch, the return line from the evaporator cold, but not frosting, the compressor is warm and running.

[Bellinghamster]

How did you determine how much refrigerant to add and what was your setup used for adding it?

Yes, overcharge is possible. Or you might have introduced some air w/ moisture into the system that's freezing in the capillary tube blocking the flow. Or accidentally let refrigerant out.

What model compressor and what is the compressor current draw (and voltage) when it's running? (deduct fan and/or water pump current and report compressor current only)

[claptrap]

The setup was to add it with a purged hose and connector from an R134a tank. To be honest I just guessed the amount.

The current draw of the compressor is 5.4A (measured at the compressor). The compressor is an isotherm G150 rated at 72W.

The evaporation/return side of the pipe is cold and does form some condensation, so it seems like some evapoeration is actually happening.

[Bellinghamster]

So that's a Danfoss BD35 compressor. From (questionable) memory, it should draw about 3.5A (compressor current at 12VDC, not including fans) so you're likely significantly overcharged and the evaporator is flooded with refrigerant. When charging, you should add vapor (can right side up) VERY slowly and intermittently while monitoring current and evaporator frost line, or better, use an IR gun to measure temperature drop "progression" through the maze of passageways, letting things stabilize before adding more. It can take a long time for things to stabilize (like 15-20 minutes!). Add until you reach rated current or "cold" region is close to the evaporator exit tube.
Total capacity (filling an empty/evacuated system) is only a few ounces of refrigerant, so very easy to overfill. If you had partial evaporator frosting you were probably less than an ounce low. Did you weight the can before and after adding so you know how much you put in?
Ideally you'd have someone with the right gear come recover some refrigerant, as you shouldn't vent it to atmosphere.

[claptrap]

I deducted the fan current (0.4A) from the measured current at the compressor.
But how is the compressor that is rated at 72W supposed to only draw 3.5A at 12V? That does not seem to add up.

[Emmalina]

Funny thing I have 2 BD35 compressors one with the old style control box (heatsink) draws 5-6 amps. The other one with a new style controll box (no heatsink) draws 4.5 ! Both work very well.

[wholybee]

Originally Posted by claptrap

I deducted the fan current (0.4A) from the measured current at the compressor.
But how is the compressor that is rated at 72W supposed to only draw 3.5A at 12V? That does not seem to add up.

You can change the resistor to set the compressor speed. The speed should be matched to the plate and size box you have. So, with a resistor for a slower speed, the compressor will only draw 3.5A. But if you swap that resistor, you get a higher speed and more current would be used.

The 72W rating is for max consumption, not what it might be setup for.

[Bellinghamster]

The nameplate wattage of the "system" would include the fan power. Fan current (therefore power) likely increases with voltage. The fridge compressor current will decrease with voltage, so I find it easiest to consider compressor current only when troubleshooting/tuning. I've found most "fridge" BD35s I've dealt with to draw around 3.5A at 13.8V, (or closer to 4A at 12V). Freezers typically run higher RPM and around 4-5A.

[Bowdrie]

Originally Posted by Bellinghamster

so you're likely significantly overcharged and the evaporator is flooded with refrigerant.

Ideally you'd have someone with the right gear come recover some refrigerant, as you shouldn't vent it to atmosphere.

Yes, probably overcharged, little expansion of refrigerant taking place.
A tech with the recovery equipment doing a service call might charge what?
Probably a hundred bucks at least, maybe more, for a couple of ounces?
That's called "minimus" by the EPA.
The guys doing work on 100 ton chiller units have more than that just occupying the volume in the hoses.

[claptrap]

Thanks people for all the replies so far. You've helped us tremendously!
I've got the evaporator temperature down to 1C now, so it's definitely going in the right direction. I'm also closely monitoring power consumption by the compressor in the next few hours.

[Bellinghamster]

Glad to hear it! Ideally, when things are stabilized (running for half hour or so, box reasonably cold) you want the "cold progression" (i.e. frost line) to cover the whole evaporator, but not down the suction line leading back to the compressor, indicating all the expansion is happening in the evaporator.
Frost down the suction line is wasted energy.

[claptrap]

The evaporator is now sitting at -4.5C (basically all over the plate), but there is no frosting yet. I shut down the fridge over the night because of the curiously high current draw, so I think it first needs to cool down a bit for the frosting to show up...

[GordMay]

How to Check the Refrigerant Charge in R134a Fridge or Freezer Systems
➥ https://penguinfrigo.co.uk/wp-conten...ant-Charge.pdf

The BD35 uses a dual voltage system [12 & 24V]. Max. voltage is 17V DC for a 12V DC system, and 31.5V DC for a 24V DC power supply system. It has an automatic Low Voltage cut-out, for when the battery voltage drops below 10.4V [12V], or 22.8V [24V].
See Electrical Connections, page 2:
➥ http://www.melody-in-blues.org/downl...ss%20BD35F.pdf

Danfoss BD 35 and 50F Fault Diagnostic
➥ https://penguinfrigo.co.uk/wp-conten...-Diagnosis.pdf

[claptrap]

That PDF is a trove of information, thanks for linking it.

[claptrap]

Now the evaporator is sitting at -13.5C and no frosting on the return line, so I supposed I've hit the right amount of coolant.