what problems can arise from using a TXV designed for R22 that is now converted to R4

[sabbathkeeper]

My problem is this; I have been assigned to repair a small commercial reach in freezer that is not cooling properly that originally contained R22 and was recently converted to a R404 refrigerant, including a new condensing unit plus filter drier, but no sight glass. The tech kept the original TXV in the system per the supervisors orders. I know from reading about retrofitting refrigerants, that it is recommended to change the TXV to match the new refrigerant. The evaperator is the original and since a TXV regulates superheat, what problems can arise from using a TXV designed for R22 that is now converted to R404, if any?

I do suspect that the TXV became plugged since the superheat was very high and the subcooling was high at 16* along with a hissing sound coming from the TXV. The evaperator fans would not even start since the evaperator did not get cold enough to activate the fan delay switch.

[bungalows]

Does it have a replacable power head?

[sabbathkeeper]

I do not know yet. I need to examine the system more closely, but think it might be changeable.

[fruecrue]

sight glass is a necessity on this system. The hissing sound could be due to the fact that there is not a solid column of liquid entering the TXV. Your subcooling doesn't sound too high to me, especially if there was a TXV restriction. More details would be helpful, ie. run pressures, line set length(if remote), relationship of units (rooftop, basement, under/over evap.), Load, condenser ambient, etc.

Was the original system's oil charge AB?

[jpsmith1cm]

R22 TXVs on an R404a system will tend to underfeed without attention.

Replacing it with the correct TXV is the best option.

[r404a]

jp is right. sounds like a clogged txv. makes sense to swap it now with proper txv for 404 and size it for evap btuhs not condenser hp


r404a

[jayguy]

let's think about this (i had an R22 txv installed on an R134a system before...and it worked perfectly...if it was R22).

let's assume several things:

A. -10F saturated evap temp
B. the txv is set for 10F superheat

1. at -10F, the txv will see a pressure of 24.5 psig (R404a conditions) and it will control the refrigerant to 20.5F of actual superheat which is 0.5F actual temperature BUT the R22 txv will think that it is 10F superheat

2. therefore, you can see that the evaporator will actually be starved of refrigerant...that is if the system could actually get to these conditions

[DPinst]

Would'nt the valve flood the system .
At -10 sst and 10 s/h that would give you a pressure of(0 F) 33pounds for 404.
R-22 would only exert 24 pounds.
As this is an opening force would it not flood the compressor?

[fruecrue]

Would'nt the valve flood the system .
At -10 sst and 10 s/h that would give you a pressure of(0 F) 33pounds for 404.
R-22 would only exert 24 pounds.
As this is an opening force would it not flood the compressor?

the bulb would contain R-22, which is the lower of the two pressures, as an opening force. Therefore spring and evap. pressure would throttle the valve closed more with an R-22 charged bulb than with an R-404A charged bulb.

[captinsano]

put a 502 or 404 powerhead on the valve,when I did markets I carried 2 different body size powerheads for 502 and you could use em on 404 also!While you got it pumped downe puul the guts apart and clean up the moving parts!The r22 and mineral oil would form wax so the guts can be stuck in the wax.

[Some Dude]

Just wondering why the heck anyone would replace the condenser on a reach in?

[DPinst]

You are right ,I should not write posts after consuming a few rum and cokes ,my mind goes to mush. Thank you for pointing out my mistake

[Airmechanical]

makes sense to swap it now with proper txv

it made sense to eliminate the incorrect metering device as soon as it was noticed



.

[r404a]

I remember an article a while back that said you could get by with this set up, but I always say eliminate as many possible failures that you can before they cause an issue.

r404a

[Airmechanical]

I remember an article a while back that said you could get by with this set up, but I always say eliminate as many possible failures that you can before they cause an issue.

r404a

i have gotten by with some crazy temporary set-ups but those were temporary

if you use 404a

your TXV should have an orange 404a marked on it

these days i see TXV's that allow for 2 and 3 different flavors of refrigerants

just make sure it's marked for the refrigerant that you use

however, experience will tell you the rest of the story

for example if you have an old r-12 TXV

you can use atleast 4 different refrigerants on it



.

[soonera/c]

Someone correct me if I am wrong. R-22 and R-404a are two very different chemicals with different btu capacitys for a given volume. I would think that the CV ratings of the TXV's are going to be different.