Hi....1996 Bonneville car. Heater works but sometimes the heat will not go off and it's pretty hot outside right now. Had checked and a hose was loose causing slider to hit the hose and not get over far enough to the cooling setting. The hose was tied off and repaired. Was working fine, then went to put on the air but the heat came out instead. (heater shuts off when car is off). Any ideas? Also, considering taking the dash out to look at - any ideas on how to do that? Repair shops want $1000 for labour to do that and cannot guarantee they can fix. Thank you.

Check the vaccuum lines, usually under the right side of the dash, to ensure that they are hooked up and make sure the heater shutoff valve is functional.

Thanks for your posting MrsS. How do you determine whether the heater shutoff valve is functional? Are there any tests for that that the normal person can do? I keep thinking it is something electrical............

When my housemate gets back, I will get him to sit down and explain the process for checking the valve- It is probably a mechanical, not electrical, issue.

you should be able to operate the valve by hand if not then you can remove the controller and then close/open it by hand if it dont then its stuck and you need a new one. as far as removing the dash just need a screw driver and some patience it comes out but you must be carefull nut to short out anything and most of all remember where everything goes back together. i find a camera works good for this take a pic then remove take apic then remove some more ect.as long as you have reference you can put it back together. if its vacume opperated then you should check for vacume first. just put your finger over the hole on a vacume hose and opperate the heater ect.