Originally Posted by
slc10844
I'm not familiar with the system on the 04, but normally if there is a heater control valve in the heater hose the valve is opened by vacuum. When the temp contol inside is put in a position requesting heat vacuum is sent to the valve to open. Most systems don't use the valve. The blend door inside is all they use.
OK, that makes sense. There is a vacuum line attached to the valve but nothing else so that's what made me wonder what triggered the valve to open.
It seems to me, based on what I saw today, that something would have to monitor coolant temp in order to determine when to send vacuum to that valve to open it - but I'm not used to working on such a "newfangled" vehicle and staring at all those gadgets and gewgaws under the hood gives me a headache...
I'm still leaning toward the thermostat being the culprit - it just seems to be the most logical choice... The problem is that this cold weather tears me up and I can't be out in for too long so, I'll have to wait until it warms up a bit before I can swap it out - luckily it's an easy & cheap swap...