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OROA head pressure control problem?

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Rich Traupmann

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Discussion starter · #1 ·
We replaced a 3 hp rooftop condensing unit for a medium temp walkin refrigerator.

It worked all winter, this summer we had a problem with the box being warm 45° I replaced the expansion valve with a 3 ton valve, it only had a 1.5 ton valve in it and we had very high superheat. The temp dropped down to 35°

But I had to add 20# r22 to get the sight glass to clear up , we didnt recover any gas I pumped it into the reciever ,presure tested and vaccumed the line before opening. The first day it went to 90° outside I had to recover about 5#to keep the unit from going off on high head.

Here is my question I trying to figure out wether its the OROA head pressure control or do i have a reciever with no dip tube to the bottom or am I missing something. There is no trouble shooting guide for the OROA.
Thanks
Rich Traupmann
 
#5 ·
the changing to a three ton valve worries me. It is likely that the valve may definately not supposed to be three ton, as this is a medium temp box. Size txv to evap load and btuh at design temp, not condenser HP.


r404a
 
#7 ·
Size the TX valve to the evaporator coil..makes sense, I can't count the number of units that I come across in the spring with an overcharge. This is not always the mechanics fault, typically I see receivers undersized as a cost cutting measure, or the length of the piping run exceeds manufactures specs, either way your flashing in the winter or overcharged in the summer.
 
Discussion starter · #9 ·
2 ton expansion valve

The problem turned out to be that the 3 ton expansion valve is to big for the job its allowing to much gas through. The manufacturer of the evaporator coil told me to use a 2 ton valve, a 1 1/2 ton valve is to small ( they dont make a 2 ton valve). I removed some refrigerent and undercharged the unit, it worked fine throgh out the summer of 2010. I may put a crankcase pressure regulator on it in the spring or not.
Rich Traupmann
 
#11 ·
a balanced cpr valve wil give you a much better range for your load demands. but why the cpr valve? is it overloading for amp draw, or is it flooding back. if it's flood back you need to adjust or replace your txv.
 
#12 ·
I STILL think you have problems at the receiver.

Yeah, the valve sizing is an issue, but this isn't adding up.

I would put the 1 1/2 ton valve back in it (What was there when you started) and start troubleshooting all over again.

You missed something, friend.
 
Discussion starter · #13 ·
I did this job over a year ago so I dont have all the information. When we had a 1 1/2 ton valve on we couldnt maintain temperature on a hot day, and the suction pressure was low about 30# on a r 22 system.
I installed the 3 ton valve and the suction pressure went up to 60# and I had good superheat. The coil is a larkin LF-190 (thank god for smart phones, i still have info on my phone) about 18000 btu according to Larkin. If I remember correctly I had over 20° super heat on the suction line before the condensing unit so its not flooding. What I think I did by installing a bigger valve is increased the capicity of the evaporator. This evaporator is over 6' long and has 2 fans in it. Sort of like matching a 3 ton air handler on a 2 ton condensing unit. You end up overloading the condenser.
Rich
 
#15 ·
Rich Traupmann said:
I did this job over a year ago so I dont have all the information. When we had a 1 1/2 ton valve on we couldnt maintain temperature on a hot day, and the suction pressure was low about 30# on a r 22 system.
I installed the 3 ton valve and the suction pressure went up to 60# and I had good superheat. The coil is a larkin LF-190 (thank god for smart phones, i still have info on my phone) about 18000 btu according to Larkin. If I remember correctly I had over 20° super heat on the suction line before the condensing unit so its not flooding. What I think I did by installing a bigger valve is increased the capicity of the evaporator. This evaporator is over 6' long and has 2 fans in it. Sort of like matching a 3 ton air handler on a 2 ton condensing unit. You end up overloading the condenser.
Rich
Click to expand...
Last I checked, 18000 btus was 1.5 tons.

If you put too large of a TXV on the coil, all it is going to do is flood your compressor, not increase the BTU capacity of the coil itself.

You aren't overloading anything, you are overlooking something.

A CPR valve isn't likely to do anything for you in this case.

Install the correct valve, charge to 90-30-1 that I posted earlier and see what happens.
 
#16 ·
jpsmith1cm said:
Last I checked, 18000 btus was 1.5 tons.

If you put too large of a TXV on the coil, all it is going to do is flood your compressor, not increase the BTU capacity of the coil itself.

You aren't overloading anything, you are overlooking something.

A CPR valve isn't likely to do anything for you in this case.

Install the correct valve, charge to 90-30-1 that I posted earlier and see what happens.
Click to expand...

X2
 
#18 ·
12,000 btu's in a ton, 18,000 is a 1.5 tons, you origally had a bad txv. Second we dont know what the superheat was when the unit was origally charged, high superheat but possibly still maintaing, that was till it hit 90 O.A. Now you replace the txv and likly set superheat to 10-12 deg, now properly flooding out the evap, hence needing more gas. Keep in mind you likey over charge the unit due to charging by sight glass, you must torch the reciever, I don't now how long it took to complete charge but a warm box with a large load and the txv was likly wide open for the most part, and once it started to maintain and pinching off txv, coil would have less liquid in it. Bottom line is, bad valve and we don't know what we started with for liquid.
 
#19 ·
Nutz said:
12,000 btu's in a ton, 18,000 is a 1.5 tons, you origally had a bad txv. Second we dont know what the superheat was when the unit was origally charged, high superheat but possibly still maintaing, that was till it hit 90 O.A. Now you replace the txv and likly set superheat to 10-12 deg, now properly flooding out the evap, hence needing more gas. Keep in mind you likey over charge the unit due to charging by sight glass, you must torch the reciever, I don't now how long it took to complete charge but a warm box with a large load and the txv was likly wide open for the most part, and once it started to maintain and pinching off txv, coil would have less liquid in it. Bottom line is, bad valve and we don't know what we started with for liquid.
Click to expand...
Sorry, friend, but I've got to call you here.

You are completely incorrect about what happens when charging a hot system.

Charging a refrigeration system like this one by a sightglass and the 90-30-1 document that has been posted is the ONLY way to do it.

When the evaporator is warm and running a high superheat there is LESS liquid in it, NOT more. Think about it for a little while.

Now, once the system starts to reach temp and the superheat comes down, there will be MORE liquid in the evaporator, requiring MORE refrigerant in the system.
 
#20 ·
I have seen many receivers undersized on condensing units. This means that when u clear the sight glass in the winter time with a flooded condensor, it may be overcharged in the summer. We have added additional receivers on many units. Other unit were just charged with as much gas as possible and they flash in the winter but still make temp. Hope this helps.
 
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