APU coolant leak ... below freezing temps

I had my 2019 Kenworth in the shop last weekend when the highs were in the low 20s .. I have a Tripac Evolution APU unit on it ... when I picked it up they had turned the APU off at the motor switch ... I started the truck to let it warm up and I noticed a leak coming from the APU box ... opened it up and couldn't really tell where the leak was coming from so I shut the valves off to keep the coolant from going back to the unit ... today it was warmer and I pulled the top and bottom covers ... I could see coolant but couldnt tell where it was coming from so I wiped it off and tried to recreate the situation ... coolant valves open APU off truck running ... but I had no leak that I could see anywhere ... left the valves open truck off and turned the APU switch to on and on the inside as well ... APU started ... still did not see a leak

could this have been from the frigid temperatures ... maybe an overflow (but I didnt notice any wetness on the overflow tube) ... I went ahead and shut the valves back off and turned the APU switch off for now but Im not sure where to start looking

any ideas ...TIA

 

Couldn't get a great look at it for where the APU is mounted but I didn't see any leaks after recreating the situation ... Wouldn't it have leaked now if it was a hose or the pump itself... I mean it was a pretty good leak

 

When I initially found it after picking it up from the shop the truck was still cold ... It had only been running for a minute or two ... Wasn't warmed up yet