Water cooled condenser pucture problem

[jayryu]

Walk in cooler in R12 system, I found some gas shortage problem. I doubted and checked water cooled condenser for leaking, but I thought it was no problem. Just after that I had to change the compressor and txv for modifying the system from R12 to R404a due to compressor trouble.
After modifying the system, it worked fine about 8 hours, but later I found the coaxial water condenser punctured. I had to replaced the coaxial condenser and it took me some days to remove water inside the system.
All the job was finished fine and the walk-in cooler is working fine.

But problem is the owner is not going to pay me the job cost of replacing coaxial condenser and water removing works etc. The reason is it was my fault to make the water cooled condenser punctured. The punctured coaxial condenser was used in R12 system and after modifying the system to R404a was punctured. Do you think it was my fault?
How can I explain to the owner it was not my fault?

[frank]

Look at the difference in discharge pressures for the types of refrigerant used

[jayryu]

About 70 psi difference. The maximum allowable pressure endurance of coaxial condenser was 500psi indicated on label.

[frank]

From the charts I am using, R12 @ 35.6C = 109.8 psig, R404a @ 35.6C = 223.4 psig

You have changed the system from LBP to HBP

I would be surprised if a condenser rated for R12 has a test pressure of 500 psig?

[jayryu]

There was some misunderstanding "frank".
500 psi in not actual pressure. it is max. allowable press. of coaxial condenser indicated by manufacturer.
Actual pressure was , R414b ; 160psi, R404a ; 230psi.