actually ,B737MRG, pack trip off NNC, has no mention of isolation valve....what QRH are you using?
only temp select to warmer,and trip reset switch push.....
The pack should not be selected off.....it is closed automatically due to temperature exceeding limits.No mention for pack selected off.
It's the same for classics or NG.
I wonder what qrh are you using guys?
Now,for a bleed trip off,after pushing the reset switch,with no effect,you should select the affected pack to off.
You'll say now,what if the other pack fails?....what if?....
You should read page CI.2.4.....it's in all types of planes I know off:
'pilots must be aware that checklists cannot be created for all conceivable situations and are not intended to replace good judgement.In some conditions ,deviations from check;lists may,at captain discretion,be needed.'
So,select second pack off,first bleed off,first pack on....work for you?
Or,if you want to do it by the book,follow the both pack trip off light..no pack available....(if you doesn't feel too safe on your knowledge about the aircraft)
Brgds