Hello to all a question about hvac system. I have a 1993 940 turbo and the ventillation fan is worrying me. When driving in low or no boost conditions the fan seems to work great, but, under acceleration the fan seems to stop blowing. I have searched the faq and am aware of the check valve, vacuum lines and vacuum pods/diaphrams under the center console possibly being problematic. I guess my question is how can I find out which component is the culprit. I have physically blown into the check and it seems to only let air pass in one direction but how reliable was my test. As far as the rest of the system I am unsure as how to test it. Thanks in advance.