Some help for me please.

[Frikkie]

Hello everyone,

I'm new to this forum and look forward to reading more about refrigeration. I am not a fridge repairer by school but I have been repairing my fridges for forty years.

I have a walk in cold room which is 1 horse power compresser using r12 gas. It had a gas leak. I have repaired the pipe work and my gas bottle was finished and there is no more available anymore. I have used lpg gas which I flushed through the loose pipework first then gassed the machine until the sight glass was full.

The fridge is working well, it is actually colder than it was now i have set the pressure switch and the suction pipe at the compresser is wet with condensation when the machine is running for a while.

My question is that on my blue guage it shows that it is almost on zero when the machine runs and the room is cold. When it was using r12 gas the guage was around 100kpaskals when it was this temperature. Will this damage the motor or do you think it will be fine.

Thanks for reading and halping.

The compresser is an 220 volt Electrolux but the numbers have gone. It is definitely one horse power.

[coolstuf]

Hi Frikkie,

Please be very careful. Only use LPG for systems specifically designed for that gas. Rather use a drop in replacement like R413A.

Moenie kanse vat nie!:p

[carlfoster]

Why are you using LPG? This can not replace R12 and you won't get the same results, and seeing it is a fuel I'd be worried about it coming in contact with the electric motor in the compressor!!!

[Frikkie]

Hi coolstuff, thanks for the advice, the only drop in we have around here is 134a but I was told that it causes oil problems. I used it on one of my bitzer compressers and had to rebuild it wit new bearings after less that a year. Until I have other gasses I must take the chance.
Dankie boet.

Hello Carl Foster
We often use lpg on the r12 machines without problems now r12 has finished. It is fuel if it burns with air only but there is no air in my cold room refridgeration or compresser motor. I was just worried about the pressure being so low on the cold side. Usually the pressures are almost the same as r12 but not this time.

I can increase the pressure by blocking some of the condenser off. In winter like now that can be fine but I do not want to do this in summer when the temperatures are vary hot.

[Brian_UK]

Why are you using LPG? This can not replace R12 and you won't get the same results, and seeing it is a fuel I'd be worried about it coming in contact with the electric motor in the compressor!!!
Without oxygen there will not be a combustible mixture.

[coolstuf]

Hi Frikkie,

You can use R134a as a drop in for R12, but you have to make sure you have POE or PAG oil in your system. Thats what's handy with a dropin, no oil change. I understand,the dropins must be very expensive in SA.
I don't understand your statement of no air in the coldroom?

[philfridge]

You could try fitting a pressure switch onto the reciever/ high side and wiring the condenser fan motor to operate through this switch which could stop the gas overcondensing causing low suction pressure.

[Frikkie]

Hi coolstuff,

An oil change is difficult with the black dome compressers, also they stopped the f11 we used to use for flushing out the old oil. It's funny really, with all the new gasses we need it more now but it has also been given the chop.

The LPG works ok as a drop in with the old oil which is why we use it. I don't think the new gasses are expensive in SA from reading on this forum but there are too many gasses now for us to keep our own stocks locally especially with the oils as well. I am worried for when our 502 gas will be finished because it will start over again with the freezer rooms which is already problems on some other farms.

Hello philridge,

The pressure switch that is on this cold room has a high side and a low side switch inside it. It was from a freezer room previous. The high switch is spare because this machine has a thermostat on the condenser for over heat shut down. Can I use the spare high side switch to do what you are suggesting. Do you think it is necessary? Will the low pressure at 100 Kilopaskals cause the machine to damage?

[philfridge]

Can I use the spare high side switch to do what you are suggesting. Do you think it is necessary? Will the low pressure at 100 Kilopaskals cause the machine to damage?

I think you would need a seperate pressure switch as the contacts are combined on a dual pressure switch . I think this may only be neccesary in winter if the condenser unit is outdoors in a low ambient temperature. The pressure you have got on the low side 100 Kilopaskals is not going to damage the compressor anyway.

[Frikkie]

Thank you for all the help. I am very glad to have found this forum. I am looking forward to some reading and learning at another time. Can I also use another computer to come here with my same name and password or can I only come here from this computer only?

[Gary]

The characteristics of propane are very similar to R22. You may need to change to an R22 TXV and change the pressure settings accordingly. Of course, this assumes that your LPG contains a high proportion of propane.

[coolstuf]

Hi Frikkie,

You can use any computer. :D

[Frikkie]

Thank you for the ideas. You have all been very kind.

Hello Gary,
If I use a r22 expansion valve would I keep the same orafice inside it or would the size change? I already tried opening the expansion valve a small amount to make the low pressure higher but it then makes frosty on the suction pipe and some on the compresser.
The LPG we get is only propane gas and I have used the old f12 valve always in the past with LPG. I thought that if the machine made cold and sweating on the suction pipe at the compresser the valve was correct size and settings good. The glass is clear and the filter is not above body heat maybe 25 C. The fins are clean on the condenser and evaporater. The room is working beautifully except for the cold side pressure lower than I had expected.

Mnr Coolstuf, Thank you for you offer, I am at my daughters house when I came to this forum. I also have a computer at home but the internet is on my telephone dial up and is slow. We are too far from the exchange to have a faster internet. Can the forum work from any computer?

[coolstuf]

Hi Frikkie,

You can use any computer, all you need is access to the internet.

[coolstuf]

Frikkie,

Google hydrocarbons21.com. Read all the safety info and max charges.

[Gary]

Hello Gary,
If I use a r22 expansion valve would I keep the same orafice inside it or would the size change? I already tried opening the expansion valve a small amount to make the low pressure higher but it then makes frosty on the suction pipe and some on the compresser.


You may find this thread helpful:

http://www.refrigeration-engineer.com/forums/showthread.php?t=19701

[Frikkie]

Frikkie,

Google hydrocarbons21.com. Read all the safety info and max charges.
Thank you for the site. I will take time there to read more and hopefully learn more.


You may find this thread helpful:

http://www.refrigeration-engineer.com/forums/showthread.php?t=19701
I read the page here and it is very helpfull, I will leave the valve without adjusting in the future.
I also looked for information about the expansion valve with google but I now have more questions.

The valve on my machine is a internaly equalised valve. I have read in one place that the sense bulb on the valve has a gas charge that should not be similar to the gas in the refridgeration system or it can make problems with hunting at some temperature ranges. Is for this reason the r22 valve better to use with propane than the r12 valve ?

Sorry if my questions are obvious answers. Thank you again for your help and long patience I have much to learn about this and many other things.

Frikkie.

[Gary]

Different refrigerants have different pressures. The TXV controls the flow of refrigerant through the coil by balancing the pressure in the coil against the pressure in the sensing bulb. Given a different refrigerant the pressure in the coil is not what the TXV is designed for, so the TXV is unbalanced and will overfeed or underfeed the coil as the heat load changes. At the very least this will reduce the efficiency/capacity of the system and can possibly damage the compressor.

The pressure range of R22 is very close to the pressure range of propane, so an R22 TXV will work much better.

[carlfoster]

Without oxygen there will not be a combustible mixture.

Of course:o How stupid of me.

If the pressure of R22 is very similar to propane, then why not just use R22? You can get that in SA still can't you? And it will use the same oil as R12 so no need for a change there.

[Frikkie]

Hi Gary,

I took your advice and fitted a r22 expansion valve and also new filter. When the machine first ran after the change valve the room was still cold (about 10C) inside. The top pipes on the evaporater were slippery ice, the bottom pipes rows on the evaporater were not cold and the suction pipe at the compresser was body warm, the sight glass was clear. The suction pressure was just a little in vacuum.

I know I probably should not but I adjusted the valve to get the suction of the compresser cool, the sight glass was bubbly for some minutes but went clear on its own and I left it to ran for 20 minutes. Then the suction was at 290 Kpa and the suction pipe was just a little wet.

The coldroom is faster to come down in temperature with this valve I notice. I will watch for a few days for problems but I tyhink it is right.

Hi Carlfoster,
r22 is the cheapest gas other than LPG in South Africa. It was getting cheaper last year when I bought some. I think it will be cheaper again when they no more use in Europe. I did not use r22 in r12 fridges because I was told propane was better for the r12 machine. Propane is used here for a long time for r12 fridges with few problems. Why only this coldroom was low suction I do not know. The coldroom compresser is 15 years old so I think in a few years it will no longer be a problem for us when it stops working and I must buy a new one.

All the people here have been very kind with information for me, I was lucky to come here. I have learned a lot from the information her and I will try to help in the electrical section sometime if I can. I am electrical qualified for many years with experiance in teaching railways and industrial but only little refridgeration.

Thank you everyone.
Frikkie