Here is my problem on my 89 rs 305 type e engine. the black plastic valve that is on top of my passenger side valve cover that routes the hot coolant through the heater core is not operating when i turn the heater on and the setting to hot. the vaccuum line that opens the black valve is not getting vacuum and the line routes up through the wiring looms, hard to track without a lot of cutting. any thoughts of how to troubleshoot? that particular line had actuall come undone from the plastic valve for a week before i notices and plugged it back in. but now, no warm coolant to the heater core. I am about to give my car to my bro for his first musclecar to work on with him and want it basically sound. any thoughts are welcome.

john

 

The way I understood it, that valve only gets vacuum when you're on the max AC setting. It's supposed to cut off the coolant flow to the heater core to maximize the AC output in that position.

If you aren't getting any heat, I don't think it would be because you don't have any vacuum to that valve.

 

The valve can get sticky, though. You can feel the hose leading from the valve to the heater core. Turn it to heat once the engine is fully warmed over and see if that hose is as hot as the one leading from the engine to the valve.

You're in So Cal, you don't need heat.

 

40 degrees is a lot colder in SoCal than it is in Colorado or Michigan.

Didn't believe it until I had been there for a year.

 

Yeah, it's only supposed to get vacuum when set or Max A/C or the hot/cold selector is turned all the way to Cold (I forget which and they may have changed it over the years). It's default is to send coolant through the heater core.

It could be the valve is sticky or it could also be that the heater core is plugged up. Whenever I do a coolant flush I take off the hoses and use a garden hose to flush fresh water through the heater core in the REVERSE direction from how it normally flows. If it hasn't been done in a while (or ever) you'd be surprised the crud that can come out!

I had a 91 GMC Jimmy with barely functional heat a few years back. I reverse-flushed the heater core as it and it was about 80% improved afterwords! Not perfect, but a LOT better.

 

I thought the valve opened to let hot coolant flow through the heater core for the fan to blow across to provide heated air to the interior... I have the prestone backflush kit installed on the car. the prob i got is not getting vacuum to the plastic valve for it to open to let the hot coolant through.

thank you for the input so far.

john

 

I haven't heard any more suggestions yet so i guess i will try to backflush it this weekend and see if that helps. And i agree that i don't really need heat in so cal, but i like the option of turning it on to bring down engine temps a little if i start to overheat .

 

i think the line only holds a vacuum when the a/c is on...or when you have the selector to the cool side...my problem was a clogged heater core i changed that and it works great now