This version will send only the target temperatures.
It should send "S" followed by carriage return
Then it should send 12 digits (4 sensors * 3 digits) followed by carriage return
It should then wait 3 seconds to give you time to process stuff, then it will query everything and expect all 108 characters back.
It will then wait 4 seconds, and display what it received
Instead, try:
It should send "S"(single character, no carriage return)
It should wait for the PIC to reply with "K" (or your favorite acknowledge character)
Then it should send 12 digits (4 sensors * 3 digits) followed by carriage return
It should then wait 3 seconds to give you time to process stuff, then it will query everything and expect all 108 characters back.
It will then wait 4 seconds, and display what it received
Then in your main loop add something like:
nTest var byte

Code:
If PIR1.5 = 1 Then 'check to see if there is data in the serial buffer
	HSERIN[nTest]
	if nTest = "S" then
		HSEROUT["K"]  'Let the PC know to start sending data
		HSERIN[....all the rest of your stuff...]
	endif
endif
I suspect the PIC appears to lock because it misses a byte. The above slows everything just a little and uses a positive acknowledgement to make sure everything is set.

Hope this helps somehow...

Best Regards,
Paul