What causes this APU problem

I’m about to have my thermo king tripac evolution APU worked on for the 5th time in the past 3 weeks, because the a/c still cuts out in the middle of the night. This is accompanied with the ! Icon near the controls.

They cut the drainage tube first, which seemed to solve the problem for 2 weeks. During that time they also did an oil change. When the problem resurfaced they checked for leaks, added more freon, and replaced a shraeder valve that the mechanic said was leaking. Third time out of the shop that same night the error happened again.

After the 4th and latest attempt...one night okay (temps dropped to 60 degrees that night, so I didn’t need the a/c to run very hard). Next night (last night) a/c cut out again.

Motor still runs despite a/c cutting off.

I spoke with another driver who said he had the same issue with his apu last year. They tried many different things, that didn’t work until they replaced the circuit board, which solved the problem.

Any other ideas?

This seems to happen after the unit has been running for six hours. If I switch to fan mode for a few minutes, then Turn the unit off, then turn it back on. I can get another five or six hours of a/c.

If I just turn it off for a few seconds, then immediately turn it back on to a/c mode, it cuts out within ten minutes.

 

So the Thermo King technician got under the bunk and moved temperature sensor on coil closer to the small pipes where freon enters.

He also set the low temperature to 60F. It was at 40F.

His reasoning is that the coil is freezing up, since the system isn’t being triggered to defrost the coil.

Well this theory is probably wrong, because the A/C & fan cut out again last night with the ! Icon.

 

No, usually only about once a month.

 

Ok thanks for the suggestions. The unit has now worked successfully 2 nights in a row. I don’t know why, because 3 nights ago (the night after leaving the thermoking) it failed. Since then we haven’t done any work to it, so I’m not sure why it’s worked 2 nights in a row.

Of course I left it in the shop in El Paso last night to show them. Not sure what to do now.

I think it might have something to do with the outside humidity, since it’s never messed up when I’m in the western USA.