Condenser restriction

[Darakuta]

Hi all,

Had a 404a secondhand installed a couple weeks ago. It was running fine for about a month, then had it switched off for about a month. After restarting, the system wouldn't function. Hooked up the guages, high side slightly low (175 psi), low side very low (10 psi). Added charge till high side was 210 psi. Low side did not get higher than 15 psi. Changed the liquid line filter and cleaned the TXV screen - no change. View glass dry, flash gas only from time to time.

The liquid line coming from the compressor going to the condenser gets extremely hot after only a few minutes (130 °F). Because of this I can only run the unit for a few minutes, not sure if compressor can handle the heat - so superheat and subcooling are probably not useable. Except for the first few loops the rest of the condensor stays at room temperature.

I would expect the sight glass to be full of liquid if the restriction would be at the TXV, correct? I checked the solenoid valve too. Am I overlooking something, or is the logical conclusion that I should try to clean the condensor?

Any help or suggestions are much appreciated as I am located in the middle of nowhere in Tanzania - the nearest technician is about 700 km away and due to his workload may have months before he has time.

Thanks and best regards

Florian

[seanf]

Do you have a access valve on the liquid line you could connect your gauge to?

Is there a point anywhere along the pipework before the TXV that is frosting/got condensation on it? Or is it just the TXV thats got frosting/condensation on it?

[RANGER1]

Florian,
You mention 130 deg F on liquid line between compressor & condenser.
Are you sure this is not discharge line?
This is normal for discharge line.
I think add a bit more refrigerant & see what happens.
Seems like you have a leak somewhere.

[Darakuta]

Hello Ranger , thanks a lot for your feedback, it was very helpful. Yes I was measuring the discharge line instead of the evaporator temp! This made me realise I have to research more!

Basically the unit was low on charge as suggested - I found a leak on the inlet low side valve.

However, the saga goes on... the salesman who sold me the unit told me that, although it was a freezer, it could be used as a chiller. Now, after checking the specs for the correct charge, I believe this is not true. It's a Tecumseh TFH2511Z, which is described as a LBP unit that is supposed to run below 14 °F.

I guess this means I would damage the compressor if I run the unit at a box temperature of 35-39 °F?

Second problem: I can't clear the sight glass. There is no headmaster valve installed. The unit has a cycling condenser fan and a receiver. When it restarts after pump-down, the low side pressure increases to about 50 psi, high side to 250 psi. Then the fan kicks in and levels the low side out at 40-45 psi. The high side drops to about 220 psi, sometimes to 210 which causes the fan to switch off. A few seconds later psi rises again causing the fan to switch on again. The sight glass never clears, though it gets better when the fan is off. This is at an outside temperature of 82 °F and a box temp of around 37 °F. I assume these pressure values are toxic for the compressor?

If I switch the compressor to a MBP, would I also need a new TxV? Sadly name plates on the condensor and evaporator.

Thanks again,

Florian

[RANGER1]

Florian,
Try running lower discharge pressure.
Lower cut in & out, as 220 psi cut in 190 psi cut out, see what happens.
Compressor probably has thermal overload to protect it.
As previously suggested check or ideally change filter drier.

Check amps if close to maximum, if okay let it run, add more refrigerant.
82 deg F not to hot, condenser fan will work itself out then.
Again check for more leaks.


Note R404a has to be charges as a liquid, preferably into liquid line, not compressor suction.
If you have had a few leaks & topped up, best change complete refrigerant charge.