i get hot air from drivers side vent and drivers side center vent but cold air

Hi
I wonder if you can help me with a problem with my BMW 728i 1996.
when the heater is on i get hot air from drivers side vent and drivers side center vent but cold air from the passenger side.
this is the same regardless of where the position selector is.
very strange only happened after i rplaced a ruptured expansion tank.
any of you have an idea of what the problem is

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This post was auto-generated based upon a question asked on our tech article page here:

[Nick at Pelican Parts]

Check that there is not air trapped inthe system and the coolant level is correct. Low coolant could create a poor flow situation in the heater core, causing the coolant to cool off too soon.

- Nick

[shogun]

or one of the heater valves is stuck. Try to clean the heater valves. For the E32 and E34 there are pics for DIY on my website, E38 is similar.