You may have a blown mono-valve - it sits in the little cube to the left of the two relays you mention under an alloy cover retained by four screws with an electrical connector on top. More or less in line with the passenger's seat.
Check this forum using the search function - an easy DIY replacement and about $30. With the engine cold take the top off and pull out the valve - a slender stick-like thing. Check if the rubber diaphragm on it is torn. Is so, replace - ~$30. If it's OK, suspect your relay.