Refrigerant Gas

[Moody Mike]

Hi all,
I run an all electric boat and my refrigeration is eutectic driven by my Onan generator on 240 volts. I recently lost the gas from the system due to a corroded valve. The gas that was in the system is now illegal as its harmful to the ozone layer. The new gas the technician put in was marked general purpose. Not sure of the exact type at the moment. Now the problem is previously my freezer would pull down to minus 20 centigrade. Now it only pulls down to minus 10 which is not enough to run a eutectic system efficiently. Does anyone know if there are specific refrigerant gasses that are more suitable to Eutectic refrigeration . Any help graciously accepted. I cant find anything on Google about it.
Mike

[ranchero76]

First, try to find out what was original gas in the system (any markings on the compressor, try to find manufacturer etc). Big chance it was R-22. There are replacements for most types of refrigerants, very cheap DIY cans. Yes, some (not all) replacements might have worse characteristics than original gas.
Other possibility - using propane as refrigerant. Propane actually has better characteristics, but use it on your own risk. While propane is safe when used with care, modern world is totally crazy about safety, responsibility concerns etc, etc, so it's definitely not for everyone.

[Moody Mike]

Originally Posted by ranchero76

First, try to find out what was original gas in the system (any markings on the compressor, try to find manufacturer etc). Big chance it was R-22. There are replacements for most types of refrigerants, very cheap DIY cans. Yes, some (not all) replacements might have worse characteristics than original gas.
Other possibility - using propane as refrigerant. Propane actually has better characteristics, but use it on your own risk. While propane is safe when used with care, modern world is totally crazy about safety, responsibility concerns etc, etc, so it's definitely not for everyone.

Thanks . There is a sticker somewhere with the gas code.

[Sailmonkey]

I would actually bet that if the system is old enough it's r-12.

There are suitable replacement gasses available, but the charge will also be different than before. Not all of the replacements will cool as much as the originals. If it is r-22 you should still be able to find some of this.

[brianlara 3]

R12/22 and 134A are all pretty efficient with 12 being the best but illegal.
I've air conditioned probably 70 motor vehicles and it's possible that your system was not completely evacuated prior to regassing ( insufficient vacuum) Also possible that insufficient gas was loaded into the system. Unfortunately you need gauges to read the high and low sides of the system and you need to know the specific pressures. Not that simple unless trained.
Really, if you want it right then a fridge mech should be employed.
Probably nothing wrong with compressor or TX valve....just incorrect amount of gas. And too much gas will cause multiple problems.

[SV THIRD DAY]

Ah...but if you are changing from lets say R12 gas to R134a and have a TXV valve, you can't just swap out the refrigerant and be on your merry way. Two things have to also be done.

1. The old R12 compressor oil is not compatible with the R134a gas. So you must change the oil in the refrigeration loop. Drain, rinse out, refill and vacuum down. Of course what I just described in two sentences is a royal PITA if you don't have the equipment to do it.

2. Your TXV MUST match the gas you are using. Why...because the TXV has a sensing bulb that is filled with the refrigerant gas to actuate the TXV. If the gas in the TXV is not the same as the gas flowing in the system the relationships between temp, pressure, and refrigerant flow will be off and your system will never work right.

We do these R12 to R134a conversions literally 3-4 a month and if you don't do the two things above...you will never get the system working correctly or worse.

[leftbrainstuff]

Depending on its age it was probably R12 or R22. R12 was more common in domestic applications.

I assume its been topped up with R134A which is marginally less efficient than R12.

Your temp delta would have me looking to baseline the system in terms of any other leaks and correct refrigerant charge.

I'm also assuming the regas was completed properly and not just topped up. You can't mix gases and lubricating oil. You might also have incompatible or end of life seals throughout the system.

You might have other incompatible components in the system. Without specifics about the whole system I can't comment.

[Moody Mike]

Yes it was done properly by s reputable company . The original gas was all vacced out new dryer fitted & the cracked pipe/flange replaced. The system has shut off alarms for high & low . I saw the label on the bottle he used to refill it said general purpose. It just doesn't pull down to minus 20 centigrade like it used to. So I'm thinking the gas is not as efficient as the old stuff but what is available. That would match the R12 for performance. If I can't find anything I may have to go to a danios 12 volt system. I'm running a car 60 liter fridge / freezer for back up & it pulls down to minus 16 centigrade.

[Moody Mike]

Originally Posted by SV THIRD DAY

Ah...but if you are changing from lets say R12 gas to R134a and have a TXV valve, you can't just swap out the refrigerant and be on your merry way. Two things have to also be done.

1. The old R12 compressor oil is not compatible with the R134a gas. So you must change the oil in the refrigeration loop. Drain, rinse out, refill and vacuum down. Of course what I just described in two sentences is a royal PITA if you don't have the equipment to do it.

2. Your TXV MUST match the gas you are using. Why...because the TXV has a sensing bulb that is filled with the refrigerant gas to actuate the TXV. If the gas in the TXV is not the same as the gas flowing in the system the relationships between temp, pressure, and refrigerant flow will be off and your system will never work right.

We do these R12 to R134a conversions literally 3-4 a month and if you don't do the two things above...you will never get the system working correctly or worse.

Thanks will check the invoice to see if this was done

[Moody Mike]

I found the invoice and the gas now in the system is R437A previously was R413A with Ester oil this was done in 1999 by the sticker I found on the unit. No mention of new oil on invoice.

[SV THIRD DAY]

Originally Posted by Moody Mike

I found the invoice and the gas now in the system is R437A previously was R413A with Ester oil this was done in 1999 by the sticker I found on the unit. No mention of new oil on invoice.

Have you checked the top of your TXV to see if it's matching the gas?
Oftentimes that's overlooked.

[Moody Mike]

Txv whats that ?

[Moody Mike]

This is what was done last May .

[SV THIRD DAY]

Originally Posted by Moody Mike

Txv whats that ?

If you have holding plates it will be attached to the plate and it meters in the refrigerant. It always lists the type of refrigerant it is calibrated for on the flat top of the round disk. You can see the TXV (Thermally Adjusting Valve) in the photo above on the left side of the plate.

[Get-away]

The TX Valve as mentioned in the image posted above this post has an acorn nut on the left side as you look at it. Remove that nut and there is a slotted screw for super-heat adjustment inside. In short it modulates the opening & closing of the TX valve relative to the sensing bulb when the unit is running.

Ideally to maximize efficiency, the TX valve needs to be closing down right at the threshold of your low pressure cutout. With the system running from relatively warm, the valve will be open further and you'll often hear the TX valve hissing this gradually drops off as the holding plate cools down.

You can adjust the super-heat to balance the system - never adjust more than a quarter turn. Without gauges its difficult, however frosting on the suction side return can be used as a guideline when the unit is at its coldest. Use the low pressure switch setting as the fixed known pressure point - (more on that further down)

You do not want the frosting to reach close to the compressor - TX open too much. Likewise the outlet of the plate should be frosted if its not, the the TX valve is probably closing too soon. All of this needs to be done at the end of the cycle. Thermostatic controls will often cut the compressor too soon so set it to max or the equivalent of always on for adjustment purposes. Additional factors are the distance between the outlet of the plate how much of the return is insulated and if you have a receiver in the system or not.

Back to that low pressure switch - most, you can see the set point - for your system -20C is 6.38PSI on the return vapor line - I'd set the LP switch to 5PSI which will be about -21C.

Keep the compressor running by maxing the thermostat. Let the system pull down to as cold as you think it will currently go, afterwards adjust the super-heat gradually 1/4 turn at a time and waiting (always with compressor running) 5-15 minutes. If you close it down too much the pressure will drop and the LP switch will shut off the compressor too early, if open too much icing will form too close to the compressor putting it at risk of damage from liquid refrigerant and the pressure will not drop. Its a balancing act between amount of icing on the return and super-heat adjustment. Not for the faint hearted but doable without gauges if careful & making slow incremental adjustments.

If you can determine whether there is a receiver in the system or not, that would help - its better to have one, you can use it as your frost reference point - adjust super-heat until frosting has reached the inlet of the receiver only, no further. The receiver is used to pump the system down and as a large expansion tank to prevent liquid refrigerant reaching the compressor - basically a large can allowing any liquid slugs to boil off in the largish open space and last component on the return side before the compressor.

A couple of pics of the compressor and associated pipework close by would help me show you where I would find acceptable as my frost cutoff point if you can't find a receiver in the system.

In summary, r437a should be quite capable of pulling a hold over plate system down to -20C and needs to be set up accordingly. See the pressure chart linked below.

https://www.agas.co.uk/media/2418/r4...s-pt-chart.pdf