Styling myself as somewhat of a VW electrical whiz, I'd like to help.  
     However description of the problem as "upper fuse" (versus lower 
     fuse?) perplexes me since my '91 would be better described as having, 
     "a forward fuse and a rearward fuse" on the wall panel behind the 
     driver's seat and the wiring diagram in my Bentley book really doesn't 
     describe the orientation.
     
     But I digress.
     
     From what I've been able to tell, there should be an 8A fuse (usually 
     white) and a 16A fuse (usually red) in this auxilliary fuse block.  I 
     recall that the 16A fuse only runs the 12V heating element for the 
     fridge (and according to legend, is fed by a relay which only gives it 
     power when the alternator is spinning).
     
     The 8A fuse runs the pump, the fridge fan, the indicator panel on the 
     front of the sink/stove/fridge, and on the 182B fridge at least, the 
     electronic ignitor.
     
     Now, if you take the approach that none of these items alone or in 
     combination with the others should be drawing 8A, that the engineers 
     designed it this way, and heap upon this the evidence that all has 
     been working fairly well over the many years since the vehicle was 
     created, then you have to conclude that something's wrong.  And it's 
     probably not the fuse!  There's little reason to get out an ammeter 
     and measure the current draw in the system.  A little fuse has already 
     sacrificed its 8A life to tell you that it's more than 8 amps!
     
     So, if the fuse pops right when you put it in, there's either a short 
     in the wiring to any of the above listed items, or a shorted fan motor 
     on the back of the fridge (of course, the thermo switch would have to 
     be engaged), or a short in the faucet switch on the "near" side of the 
     switch, or a short in the indicator panel (and if you have a 182B, 
     possibly a short in the switch which selects propane cooling).
     
     The most direct thing to do is to find all the removable connectors 
     between the fuse and all the "components", and disconnect them; make 
     sure the fuse is good.  Then, beginning at the fuse, reconnect each 
     connector, check the fuse, then move on.  If all goes well, when you 
     reconnect the shorted wire/component, the fuse will pop.
     
     At this point, it only remains to examine the evidenced source of the 
     problem and isolate the fault, fix it, and you're back in business 
     (notice how quickly I can state what is probably the hardest part of 
     the problem?).
     
     Now you know why your shop wants so much for troubleshooting.
     
     Of course, it goes almost without saying that if the fuse pops when 
     you turn one of the components on, you've likely found your problem.
     
     BTW, check out my earlier post about the burn-up of my fridge cooling 
     fan and subsequent popping of my 8A fuse.  May be a place to start.
     
     -Blaine