Apu wont start

so I've got a thermoking apu. I got a pm don't at ta a fewhile months back and every time the apu would try to start the reset under the bunk would trip for the first try then after would start right up and run great. Every start up it would for the first one try but not start then start fine after the first try. Today just now got another pm because I was getting worried as ta. so they did the pm and now my apu wont even try to start. the guy said that the filter that's located in the back hard to get to was loose and causing air to get into the fuel line but did not understand why apu wouldn't start up after this pm. no fault codes come up. it just clicks and then the power box turns off the ac and fan and then I try again but no fault code. I tried it under fan mode same thing won't start. No one knows why under the bunk the fuses are not blown or the one on the apu. the reset fuse is not out. any ideas?

 

yes sir that's the switch on the right side. Yea it's in the on position.

 

they tried all of those even replaced starter apu still won't start

 

no at thermoking they can't figure it out. they tried a new ground still same issue

 

they have looked at all electrical and nothing is wrong electrical. it tryst one time to crank so a quick crank and then won't try any longer