In addition to the prior posting -
Last year BOTH of my Volvos had their heater cores go kaput.

The factory core on my 87 245 had a split design - where hot fluid went down each side, and returned up the center - so that one side of the car was not hotter than the other.

If there is a pinhole leak starting o the left side - that would also contribute to the one-sided situation.

I tried some radiator "stop-Leak" products - guaranteed not to plug heater cores or radiators - plugged the heater core solid!!!!

Best advice - replace the heater core (this is a big job) pronto!!!

I did my own - involved a dremel tool - cutting the right side of the shroud around the heater core and sliding the heater core out the side.

Check the archivbes here - some one had posted the steps

Give yourself a day or two for the job!!!

This rates right up there with heater fan motor replacement jobs as teh most intimate time you will spend with your Volvo.



Good Luck