reach in R134a cooler

[bluefitness]

A friend of mine has a reach in to keep flowers. The setpoint of the cooler is 47 degrees. It will maintain this temperature for a few days and then it will not drop below 70 degrees. It uses a cap tube system. It was originally R12 that was converted to R134a. The data plate does not have the weigh in charge and there is no high side port. I didn't have my tools on me when I looked at it a month ago. The condenser seemed to have a gradual decrease in temperature. There was little difference in temperature from the top of the condenser to the bottom. The temperature was higher than ambient temperature. I also could hear flashing in the evap. I initially suspected it to be low on charge. My friend told me there is a large amount of condensate that came out of the unit after it was shut off for a while. I'm assuming the unit is icing up. With no weigh in charge data, I am going to have to charge the unit using a different method. I'm ruling out a restriction based on the fact that there doesn't appear to be refrigerant backing up and the lack of subcooling. I know POE systems with cap tubes have problems with restrictions.

My problem has to do with charging a critically charged system accurately. I was taught to charge a system using a 15 degree SST below desired set point. For example, if you the box temperature was 40 degrees, the SST would be 15 degrees lower. Therefore, a 134a system would be have a low side reading of around 29 psig (25 degree saturated temp). Another way to charge it would be through superheat (20 to 30 degrees). Is this a proper way to check the charge of a unit or was I taught incorrectly?

[james122964]

best this is call the manufacturer tech support they will tell you the orginial charge weight.

If if works for a couple days then stops could be water in the system making its way around then freezing up and shutting the unit down.

Jim

[icemeister]

...I also could hear flashing in the evap. I initially suspected it to be low on charge. My friend told me there is a large amount of condensate that came out of the unit after it was shut off for a while. I'm assuming the unit is icing up...

That sound of flashing is a good indicator that you don't have a solid column of liquid to the evaporator. The large amount of condensate water after shutdown would indicate an evaporator freezeup, as you suspected.

My problem has to do with charging a critically charged system accurately. I was taught to charge a system using a 15 degree SST below desired set point. For example, if you the box temperature was 40 degrees, the SST would be 15 degrees lower. Therefore, a 134a system would be have a low side reading of around 29 psig (25 degree saturated temp). Another way to charge it would be through superheat (20 to 30 degrees). Is this a proper way to check the charge of a unit or was I taught incorrectly?

That rule-of-thumb may get you in the ball park but remember, it's just an approximation. As has been said, the best way is to get the proper charge weight for that box and charge accordingly. Short of that, use the superheat method.

One old-timer's trick to get an initial charge approximation is to charge the system with the evaporator fan(s) off and charge until you get a frost line which just reaches the compressor. then restart the fans and complete the charge by superheat.

Another one I use often, is to charge liquid to the high side (with the compressor off) until the flow stops. Then start the compressor and adjust the charge by superheat.

[bluefitness]

Thanks for all the help. I called my friend to get the model number, but half of it is not legible. Since the design temp of this box is at a lower temperature 35 to 40, should I bring the box temperature down to this point before checking for a 20 to 30 degree superheat (I'm assuming I do). The box only needs to maintain 47 to 53 degrees; it is currently set to maintain 47 degrees. Another problem with this box is the ambient temperature can reach 95 plus degrees (located in unconditioned space). I doubt the cooler was designed for this temperature range. I will bring a saddle piercing valve (braze on type), since there isn't a high side port.

I meant to write 22psig at 25sst in the original post.

[bluefitness]

I looked at the unit yesterday:

94 ambient
33 psig suction (R134a)
liquid line temp 114 to 122
Temp difference through condenser 20 degrees
Compressor running right at RLA

The unit seemed to hover around 55 to 60 degrees. He said that it wouldn't go below 70 degrees after running for a couple of days, but he didn't remember the room temperature. I cleaned the condenser to no avail. I sprayed the condenser and the pressure dropped to 25psig and cycled off within a few minutes. The box temp is only set to 47 degrees. I pretty much told him that his problems were due to the high ambient conditions. Since I haven't done much commercial refrigeration work (mostly residential HVAC), I just wanted to make sure I'm not missing anything. I didn't add a high side fitting due to the liquid line temp. I guess I jumped to a quick diagnosis. I'm hoping someone can add some input, as the diagnosis leads to little to no solutions (other than moving the refrigerator).

[bob_scheel]

I looked at the unit yesterday:

94 ambient
33 psig suction (R134a)
liquid line temp 114 to 122
Temp difference through condenser 20 degrees
Compressor running right at RLA

The unit seemed to hover around 55 to 60 degrees. He said that it wouldn't go below 70 degrees after running for a couple of days, but he didn't remember the room temperature. I cleaned the condenser to no avail. I sprayed the condenser and the pressure dropped to 25psig and cycled off within a few minutes. The box temp is only set to 47 degrees. I pretty much told him that his problems were due to the high ambient conditions. Since I haven't done much commercial refrigeration work (mostly residential HVAC), I just wanted to make sure I'm not missing anything. I didn't add a high side fitting due to the liquid line temp. I guess I jumped to a quick diagnosis. I'm hoping someone can add some input, as the diagnosis leads to little to no solutions (other than moving the refrigerator).

Get some more air on the condenser. Put a fan or an exhaust duct near it and make sure that none of the hot air is recirculting.

You mentioned the unit was originally R-12 converted to R-134a. There is always capacity lost when this conversion is done and head pressures are usually higher. You could convert to R414b (hot shot) it has lower head pressures and less of a capacity loss. It will also work with either the POE or mineral oil.

[james122964]

I looked at the unit yesterday:

94 ambient
33 psig suction (R134a)
liquid line temp 114 to 122
Temp difference through condenser 20 degrees
Compressor running right at RLA

The unit seemed to hover around 55 to 60 degrees. He said that it wouldn't go below 70 degrees after running for a couple of days, but he didn't remember the room temperature. I cleaned the condenser to no avail. I sprayed the condenser and the pressure dropped to 25psig and cycled off within a few minutes. The box temp is only set to 47 degrees. I pretty much told him that his problems were due to the high ambient conditions. Since I haven't done much commercial refrigeration work (mostly residential HVAC), I just wanted to make sure I'm not missing anything. I didn't add a high side fitting due to the liquid line temp. I guess I jumped to a quick diagnosis. I'm hoping someone can add some input, as the diagnosis leads to little to no solutions (other than moving the refrigerator).

Your suction pressure is too high, 33psi 134a equals 38 degree coil = discharge air of 48 degrees.

I will look back and see if you mention high side pressure, I suspect you are over charged by a good bit.

Jim

[Airmechanical]

One old-timer's trick to get an initial charge approximation is to

charge the system with the evaporator fan(s) off

charge until you get a frost line which just reaches the compressor

then restart the fans and complete the charge by superheat

never thought of that one but i like the concept!

what about the old, charge it until frost just barely comes out of the evap

what about the old, "if the box is warm" charge it until you feel heat all the way down the condenser



.

[ammoniadog]

1st, check the door gaskets and make sure the door is closing properly. If that don't work....

Has this thing ever worked since someone replaced the R12 with R134a? My bet is on the cap-tube being partially plugged up with burnt POE sludge. This would require a new cap tube, filter drier, and oil replacement and/or a new compressor. Like Bob says, R134a has less capacity than R12 did, and it runs at higher discharge pressures. R134a also is supposed to have POE oil which is much more prone to problems than other oils are, especially with the high ambients you are dealing with.

If you are just messing around with this thing for the experience and challenge, and the customer is willing to pay for a bunch of parts with no guarantees, I say good luck! If you do try to fix it, try using Hot-Shot like Bob said, or R409a. Otherwise, it may be wise to try to get them to spring for a whole new flower cooler and send this one to the junk heap.

[ammoniadog]

Something else that may be going on with this thing is since the temperature control is set so high, it may reach set-point and try to short cycle too quickly. If this happens, the little fractional horsepower compressor won't be able to start up and it will trip on its overload for a few times before it's able to get going again. If this is the case, you could wire in a delay-on-break timer or a different temperature control with a wider differential to try to help. This is probably in addition to the cap tube, filter drier, and oil replacement and/or new compressor. Have fun!

[bluefitness]

Something else that may be going on with this thing is since the temperature control is set so high, it may reach set-point and try to short cycle too quickly. If this happens, the little fractional horsepower compressor won't be able to start up and it will trip on its overload for a few times before it's able to get going again. If this is the case, you could wire in a delay-on-break timer or a different temperature control with a wider differential to try to help. This is probably in addition to the cap tube, filter drier, and oil replacement and/or new compressor. Have fun!

I did notice that it cycled on within a few minutes of cycling off, so I should add a delay on break timer. It is located in a very hot area, so heat gain will cause the thermostat cycle off time to be shorter at a 95 degree ambient than 75. I also noticed the door gaskets were not in the best of shape.

The cooler is a Perlick 3 sliding door reach in. The serial number is partially rubbed off. Should this reach in be able to reach its setpoint with 95 plus ambient?

[ammoniadog]

If you have a partially blocked cap-tube you will have high superheat and flashing at the end of the cap-tube. A lot of people will see this and think the unit is low on refrigerant. Then they add more refrigerant until the suction pressure and superheat are closer to what they think it should be.

In the above scenario (which I think is very likely what happened to your cooler), the unit will be overcharged, but can still have high superheat. Also, YOU STILL DON'T KNOW WHAT YOUR SUBCOOLING IS. You need to get a guage on there (and fix the door gaskets), or tell them it's time to buy a new POS used beer cooler to keep their flowers in

As a side note... I'm sure some people have converted from R12 to R134a without changing the oil and have gotten it to work, but it's not something I think any one would advocate. R134a does not mix well with mineral oil, so it will not carry it around the system and the compressor will not get proper lubrication over time. If the compressor is on the bottom of the unit and the evaporator is on the top, it will probably work for a while, but it still is not good. Yes, R409a would be the better choice, and it would work with either type of oil.

[bluefitness]

If you have a partially blocked cap-tube you will have high superheat and flashing at the end of the cap-tube. A lot of people will see this and think the unit is low on refrigerant. Then they add more refrigerant until the suction pressure and superheat are closer to what they think it should be.

In the above scenario (which I think is very likely what happened to your cooler), the unit will be overcharged, but can still have high superheat. Also, YOU STILL DON'T KNOW WHAT YOUR SUBCOOLING IS. You need to get a guage on there (and fix the door gaskets), or tell them it's time to buy a new POS used beer cooler to keep their flowers in

As a side note... I'm sure some people have converted from R12 to R134a without changing the oil and have gotten it to work, but it's not something I think any one would advocate. R134a does not mix well with mineral oil, so it will not carry it around the system and the compressor will not get proper lubrication over time. If the compressor is on the bottom of the unit and the evaporator is on the top, it will probably work for a while, but it still is not good. Yes, R409a would be the better choice, and it would work with either type of oil.

Why would someone over charge a restriction to a point that the suction pressure is too high? The flashing can be heard now. I actually heard it. When I sprayed the water on the condenser, it went away or was less noticeable. I guess I need to put a high side access on there. Is having a 120 degree liquid line not an issue? It was hot to the touch. I measured 147 at the filter drier using an infrared thermometer. I was getting around 120 with the infrared and my fieldpiece clamp on accessory at the liquid line prior to the filter drier. I wasn't sure if the filter drier was picking up extra heat from the discharge air blowing over it. I guess I botched my diagnosis and need to relearn a lot of things.

It seems like the consensus is that it is overcharged, restricted, or both. I still don't see how it could be a restriction with a proper charge. Thanks again

[KB Cool]

Now it sounds like your condensor is dirty.

[james122964]

Why would someone over charge a restriction to a point that the suction pressure is too high? The flashing can be heard now. I actually heard it. When I sprayed the water on the condenser, it went away or was less noticeable. I guess I need to put a high side access on there. Is having a 120 degree liquid line not an issue? It was hot to the touch. I measured 147 at the filter drier using an infrared thermometer. I was getting around 120 with the infrared and my fieldpiece clamp on accessory at the liquid line prior to the filter drier. I wasn't sure if the filter drier was picking up extra heat from the discharge air blowing over it. I guess I botched my diagnosis and need to relearn a lot of things.

It seems like the consensus is that it is overcharged, restricted, or both. I still don't see how it could be a restriction with a proper charge. Thanks again

Ok, here goes.
They do not overcharge until suction pressure is to high, only high head pressure.
Your box is warm/hot, your liquid line is hot, all or nearly all the refrigerant is flashing to gas, with no or little liquid left for phase change. You will not have low superheat and high subcooling when overcharged on a hot pull down.
No high side access, compressor changed from 12 to 134, maybe all of the r12 was not removed, maybe the oil was not changed, maybe the 409a was charged with the cyclinder right side up as gas and the system is full of gas that is mostly r22, but you will never know without knowing the high side pressure.

Jim

[Tater9466]

I'm guessing you are icing back to the compressor like a mofo way overcharged

[Tater9466]

I did notice that it cycled on within a few minutes of cycling off, so I should add a delay on break timer. It is located in a very hot area, so heat gain will cause the thermostat cycle off time to be shorter at a 95 degree ambient than 75. I also noticed the door gaskets were not in the best of shape.

The cooler is a Perlick 3 sliding door reach in. The serial number is partially rubbed off. Should this reach in be able to reach its setpoint with 95 plus ambient?

It ain't gonna work being 95 and making the dude pay for gaskets that you will have to have made for him will be a waste

[james122964]

A friend of mine has a reach in to keep flowers. The setpoint of the cooler is 47 degrees. It will maintain this temperature for a few days and then it will not drop below 70 degrees. It uses a cap tube system. It was originally R12 that was converted to R134a. The data plate does not have the weigh in charge and there is no high side port. I didn't have my tools on me when I looked at it a month ago. The condenser seemed to have a gradual decrease in temperature. There was little difference in temperature from the top of the condenser to the bottom. The temperature was higher than ambient temperature. I also could hear flashing in the evap. I initially suspected it to be low on charge. My friend told me there is a large amount of condensate that came out of the unit after it was shut off for a while. I'm assuming the unit is icing up. With no weigh in charge data, I am going to have to charge the unit using a different method. I'm ruling out a restriction based on the fact that there doesn't appear to be refrigerant backing up and the lack of subcooling. I know POE systems with cap tubes have problems with restrictions.

My problem has to do with charging a critically charged system accurately. I was taught to charge a system using a 15 degree SST below desired set point. For example, if you the box temperature was 40 degrees, the SST would be 15 degrees lower. Therefore, a 134a system would be have a low side reading of around 29 psig (25 degree saturated temp). Another way to charge it would be through superheat (20 to 30 degrees). Is this a proper way to check the charge of a unit or was I taught incorrectly?

Now that I read again your original post, with the additional information you have provided I can tell you that the unit is why over charged.
The original r12 had mineral oil which is not as problamatic as poe. I would remove the charge from the system. Start over, I can not tell you the exact amount of refrigerant but for the most part these have less than 12oz of refrigerant. I would go with 6oz to start, and make sure you have access to the high and low sides of the system and pump down, I would change the oil but that adds work. after adding the 6oz wait for at least 10 min then check super heat at the compressor suction line, then add 2 more oz, wait, and so on. You are looking for around 20 degrees superheat at the compressor.
If you call around or post compressor model it will be easier to tell were you should end up.

Or you could just remove gas, wait, remove wait and so on also. I personally would rather remove the gas and start all over.

Jim

[KB Cool]

Put a high side access valve on it. And charge to 30 over ambient and then finish off with 20° SH at the compressor. Whats your high side pressure? 250?

[Dowadudda]

Now that I read again your original post, with the additional information you have provided I can tell you that the unit is why over charged.
The original r12 had mineral oil which is not as problamatic as poe. I would remove the charge from the system. Start over, I can not tell you the exact amount of refrigerant but for the most part these have less than 12oz of refrigerant. I would go with 6oz to start, and make sure you have access to the high and low sides of the system and pump down, I would change the oil but that adds work. after adding the 6oz wait for at least 10 min then check super heat at the compressor suction line, then add 2 more oz, wait, and so on. You are looking for around 20 degrees superheat at the compressor.
If you call around or post compressor model it will be easier to tell were you should end up.

Or you could just remove gas, wait, remove wait and so on also. I personally would rather remove the gas and start all over.

Jim

I have been not here much lately. seems you have come on the scene.

Nice skills. welcome to the forum