I have a 1990 GLE 16v. The AC has been converted to r134a and was working great. However recently there would be no air coming from the dash fans when going up hill. The weird thing is though is that it works just fine on straight stretches even at high revs and also while parked. When the AC is off and I'm just using regular fan mode it still happens. Sounds to me like a vacuum issue but it only happens uphill even going slow or fast at 2000 or less RPM. Any ideas?

 

You need vacuum motor #39 on the attached pdf. It ss to 9463042. Unfortunately its no longer available

Tim
800.234.5394

 

I'd replace the vacuum diverter valve under the hood... very cheap, widely available.
BTW, #39 is a bellows, not a motor, very different...

 

we call them vacuum motors - vacuum actuators - vacuum bellows - whatever. Its a round black thing with a rubber diaphragm that gets a hole in it. This one has 2 vacuum connections and when this one gets a hole in it, it prevents air from going out the dash vents under load (low vacuum conditions). We've changes many of these over the years on 740's 940's 960's for this condition.