Ever since I got my 97 XK8 the blower fan seems not to blow hard. The HVAC works correctly as for as blowing where I tell it too but it does not seem to blow all that hard though, not compared to other cars I own. I had it on defrost today and it was very weak. Odd thing is the motor sound like it is trying to blow hard but has air flow hamping going on. Sorta like a faf trying to pull air through a very dirty filter. If there somewhere I can check to see if the air flow is being restricted??

 

See some of the other posts on "blower motor". There are 2 blower motors, perhaps only one is working. Bits of foam break off and get stuck in the squirrel cage of the blower motor and cause distress on the part of the vehicle owner. Evidently using a long pick with a hook on the end to enter through the "fresh/recirc" door is the quick and easy way to get that chunk of foam out. Give it a try and post the results.