Hi guys!

When replacing the water valve in my AC equipped 740 -88 (due to leakage), I noticed that vacuum is never applied to it (it should be applied at "Max cool" and temp lever at leftmost position). This causes the heat to never cool down entirely, even when the temperature lever is in the leftmost position. I know, turning on the AC gives me cool air, but it would be nice to be able to turn off the coolant flow in the heater core completely to maximize the coolness of the incoming air.

So, my question:

Do you have any experience regarding the vacuum application control mechanism? Where to check first?

Heater flapper door is adustable via a cable behind the glove box. (in the FAQS)

Also look at pages 11-12 here for a discussion when vacuum is applied to various parts. This is for the manual climate control.

http://www.volvotips.com/service-manual/volvo-740/Volvo-740-760-780-body-interior-heating-cooling-service-manual-part-3.html
--
Post Back. That's whats makes this forum work.

Thank you for your answer.

I tried adjusting that cable as per the FAQ, but no change in water valve vacuum application.

Thank you aleekat, that was a very nice diagram!!

I have not had to dig into this particular fix yet, but have some ideas:

1. Are the controls for the various vent flaps working, i.e. if you switch between heater outlets (arrow going down) and dashboard vents (horizontal arrow), does the amount of air coming out of the different vents change? Reason I'm asking is because these are also driven by vacuum on the same control panel.

2. Source of the vacuum for the heat/air on my 1989 740 Turbo appears to come from a T-junction in a hose below and a bit in front of the throttle body - hose disappears into a corrugated black plastic tube that goes through the firewall. This has already been patched on my car. If you have no source of vacuum, nothing will work properly.

Thank you for your answer.

1. Yes, they are all working.

2. I have vacuum to the other vent valves meaning that the supply is ok.