A vacuum hose from behind the battery had a hole in it and so it was loosing suction and causing the vents to close. Probably some battery acid caused the hole? Well, cheap fix - cut a bigger piece of vacuum hose, spliced the original hose where the whole was and then inserted those two ends into the new bigger hose. Vents blow just fine now!! Costs me $0 cause the guy at the store gave me the piece of hose for free!
