Our -80 freeze just "exploded" in the lab

[Eternalightwith]

Our -85oC REVCO freezer made a pop and this nasty smell filled the lab. I was lie, it's just aerosolized oil. The service guy ran up here and I asked him what refrigerant. he said probably is propane. I was wondering, what refridgerant besodes propane could it be, was that nasty smell oil. and I wanted to know, if a girl in our lab noticed right after the pop, that the freezer was at -45 and not -82+, why would it pop? I figured it was the safety valve popping open, but why would the high side pressure be that high if the fridge was at -45oC and trying to chill it to nominal temp?

[Xeon th MG Pony]

could be the electrical?

[jinu117]

It could be at -45c instead of -85c as system overloaded (why? I don't know but could be oil logging, could be system going down hill).
When this happens, high side pressure must have been darned high to be honest if it was designed to go down to -85c and system somehow struggled to keep operating.

[star882]

Has it tripped on high pressure before?
Most likely a high pressure control failed to operate and there was a fault causing high pressure. Has the condenser ever been cleaned?

[Eternalightwith]

the whole unit is encased in sheet metal to keep away curious lab techs.
So yeah I assume it was trying to get it back down to nominal (-80ish).
I'm pretty sure the high pressure relief valve is what popped. But weird that the pressure would rise that high. I'd think the compressor would have smoked first, if there was a leak, sausing the reduction in cooling power.

[boshuter]

I think it's all a lot of guessing until someone actually looks at the unit and determines what went wrong. I've got 2 commercial cascades here (Neslab CC-100 lab chillers), and they have cutoff's that would shut them down long before pressure got high enough to blow a relief valve, I'm fairly certain that freezer would have the same protection. Keep in mind that a commercial unit is designed to be operated by people who have absolutely no knowledge of phase change.

[marru]

Another thing could be the ice buildup on the evaporator that could cause a crack on the pipes ;)
Frequent stuff if the defrost is not working right.

[Xeon th MG Pony]

Thats true high density ice makes an impressive sound when cracking!