Refrigerant Gas

[Moody Mike]

Thanks

[Moody Mike]

I can't see the Tx valve st the moment the blue box with grey top is a solenoid this was replaced due to corrosion .

[Get-away]

Originally Posted by Moody Mike

I can't see the Tx valve st the moment the blue box with grey top is a solenoid this was replaced due to corrosion .

Your system might have a fixed orifice or capillary tube setup instead of TX valve and no adjustment - I assume you're looking for it in the ice box right?

The image you just posted only lets me see mostly high pressure side piping, no low pressure or return is obvious, unless the return is the insulated pipe that looks like its running behind the condenser (box with fan).

Another thing that might help, the blue canister above the sight glass is the drier and both are installed on the high pressure side of the system. Charged properly when the comp is running (and has been running a while 10 min's or so - not first start) there should be very few or no bubbles visible in the sight glass. The aim is a solid column of liquid refrigerant reaching the expansion device whether thats a TX valve or fixed orifice / capillary tube. If there are constant bubbles or just occasional slugs of liquid showing in the sight glass, the systems likely undercharged.

[Moody Mike]

I have found a knowledgeable fridge mechanic to come have a look. Apparently I have a common problem with several of his customers having the same issues. We are looking at changing the gas to R404A which is more efficient than R437A currently being used. It will require new Tx valves & filter dryer. I'm going for a new digital thermostat as well.hopefully should get it down to minus 20 .

[Moody Mike]

Originally Posted by Get-away

Your system might have a fixed orifice or capillary tube setup instead of TX valve and no adjustment - I assume you're looking for it in the ice box right?

The image you just posted only lets me see mostly high pressure side piping, no low pressure or return is obvious, unless the return is the insulated pipe that looks like its running behind the condenser (box with fan).

Another thing that might help, the blue canister above the sight glass is the drier and both are installed on the high pressure side of the system. Charged properly when the comp is running (and has been running a while 10 min's or so - not first start) there should be very few or no bubbles visible in the sight glass. The aim is a solid column of liquid refrigerant reaching the expansion device whether thats a TX valve or fixed orifice / capillary tube. If there are constant bubbles or just occasional slugs of liquid showing in the sight glass, the systems likely undercharged.

Found the TX valves

[Moody Mike]

Originally Posted by Moody Mike

Attachment 140641
Found the TX valves

[Moody Mike]

Originally Posted by 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

There is frosting on the pipe at the top of the compressor when starting from ambient temp. But this goes away when it's pulled down & running . I had a look for the adjust but on the TX but couldn't see it. Lots of insulation glued around it.

[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.

I finally found a good Refrigeration mechanic yes he said the same going to 404 gas new TX valves etc.

[giant]

Originally Posted by 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

Great post.... thanks for explanation and link.

[Moody Mike]

Ok i had the fridge mechanic come take a look .we are booked in next month to swap the gas over to R440 along with tx valves & dryer etc. also a second solenoid for the freezer & 2 new digital thermostats plus a high pressure cut out switch. I found out the current mechanical thermostat only worked on the fridge side not the freezer. After all the work above is done i will be able to control the temps of both boxes separately. So i can have fridge freezer or two fridges or two freezers. The 440 gas is supposed to be as close to R12 as we can get. I will be very happy to have this sorted.