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Car Forum / Volvo Cars / September 2005air vents cut out under load
When accelerating or climbing a hill, the climate control of my '93 960 changes from the dash vents to the floor vents until the vacuum rebuilds. I have searched and searched for a vacuum leak. Both black/white vacuum check valves on the firewall have been replaced. The cruise control works perfectly so that portion of the system is fine. The brake booster check valves is fine. The brakes do pulse a little, maybe the vacuum leak, maybe warped rotors. This was always a cinch to fix on the 740's. Does anyone have experience correcting this symptom on the 960? Thanks. >When accelerating or climbing a hill, the climate control of my '93 960 >changes from the dash vents to the floor vents until the vacuum rebuilds. I >have searched and searched for a vacuum leak. Both black/white vacuum check >valves on the firewall have been replaced. Have you checked the double acting vacuum motor on the driver's side of the center console behind the cover on the right side of the driver's foot well? These are notorious for leaking and a pain to change unless you cut into the heat/cooling plastic box thingy. It's one of the few _really_ stupid things I have foind on the 960. That and the design of the PNP switch- but at least you don't have to disassemble the tranny to get to that. >The cruise control works >perfectly so that portion of the system is fine. The cruise control is powered by a vacuum pump that is electric and not at all related to engine manifold vacuum. >The brake booster check >valves is fine. That has a one-way valve, so once a vacuum is built up it is (or should be) held for long periods if the brakes aren't used, and since you rarely use the brakes (use the vacuum booster) when accelerating (when vacuum is the lowest) it usually won't show as a symptom. >The brakes do pulse a little, maybe the vacuum leak, maybe >warped rotors. Probably warped rotors. __ __ Randy & \ \/ /alerie's \__/olvos '90 245 Estate - '93 965 Estate "Shelby" & "Kate" It is supposed to do that to lessen the load on the engine so try not putting the pedal to the metal so hard. All the best, Peter. > When accelerating or climbing a hill, the climate control of my '93 960 > changes from the dash vents to the floor vents until the vacuum rebuilds. [quoted text clipped - 4 lines] > maybe warped rotors. This was always a cinch to fix on the 740's. Does > anyone have experience correcting this symptom on the 960? Thanks. > It is supposed to do that to lessen the load on the engine so try not > putting the pedal to the metal so hard. > > All the best, Peter. Huh? Mine never did that, though it did just start doing the exact same thing recently, it's clearly a vacuum leak as the system should hold a vacuum indefinitly even if the engine isn't running. > > It is supposed to do that to lessen the load on the engine so try not > > putting the pedal to the metal so hard. [quoted text clipped - 4 lines] > thing recently, it's clearly a vacuum leak as the system should hold a > vacuum indefinitly even if the engine isn't running. You'll find if you take the hose off the leaking side of the double acting servo and plug it, that the system will work fairly well until you get around to fixing it properly.  SignatureMike F. Thornhill (near Toronto), Ont. Replace tt with t (twice!) and remove parentheses to email me directly. (But I check the newsgroup more often than this email address.) > > > It is supposed to do that to lessen the load on the engine so try not > > > putting the pedal to the metal so hard. [quoted text clipped - 8 lines] > acting servo and plug it, that the system will work fairly well until > you get around to fixing it properly. Is this true of a 740 as well? I haven't done any investigation yet, been too busy with house projects to worry if my vents blow on hills. The 740's have a manual climate control system. The most common reason the air will come out the defroster vents instead of the dash vents is a rubber plug on an unused port in the vacuum reservoir. If I remember correctly, the reservoir is tucked behind the front bumper. The rubber plug cracks over time. With little or no vacuum, the climate control switches to the default vent mode of defrost for safety reasons. If the crack is large enough or the plug falls off, air comes out the defroster vents all the time. > Is this true of a 740 as well? I haven't done any investigation yet, been > too busy with house projects to worry if my vents blow on hills. The 740 system is completely different, and I've not had to look for a vacuum leak on it. So then answer is, I don't know, maybe. SignatureMike F. Thornhill (near Toronto), Ont. Replace tt with t (twice!) and remove parentheses to email me directly. (But I check the newsgroup more often than this email address.) |
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