radwebster

ok according to the haynes manual, i was correct in assuming that hot coolant flows through the heater core all the time, and there is just a door that regulates how much air flows either through or around the heater core. everyone that said otherwise in my earlier thread...is the haynes manual wrong, or were you guys uncertain on the operations of the system?

also, just for the record, i guess this doesn't matter any more anyway, as i already ordered a new control valve from ecklers...oh well, i am just curious now.

bogus

I think you are correct. It works this way in regards to the automatic climate control.

you need to invest in a helms manual. www.helminc.com - worth the $$$.

65Z01

That's what my '88 GM Shop Manual shows.

I agree, the official shop manual would be a big help in the future.

rons85

Well - not exactly. Yes, the air temperature is regulated by positioning a flapper door in the ductwork - blending air coming through the heater core with air directly from the base of the windshied. No, hot water does NOT flow through the heater core all the time - only when the hot water control valve is open. This is the valve that sits outside the firewall behind the right front wheel well. It is operated by vacuum, and controlled by the heater control unit inside the car, which switches the vacuum feed on or off depending on where the Temperature selector (if it's the manual control) is set, or depending on weather or not the system thinks it needs hot air (if it's the automatic control unit). If you look closely at the valve you can see that it's a bypass design - when "open" it routes coolant through the heater core, when "closed" it isolates the core and routes the coolant back to the motor - bypassing the core. This keeps hot coolant out of the interior of the car when it is not needed, and improves the efficiency of the A/C operation.
It's been said before, but I'll say it again - for those who don't listen - the Haynes manual is, at best, a POS. Get a copy of the Helms book - it's the real deal!

rustangkiller

what was your problem. my air doesnt get hot at all. theres no leak or steam comming out of the dash so i dont think the heater core is busted but maybe my valve isnt opening letting hot coolent run through the heater core. if there is a manual switch can you switch it to stay on. just during the winter month. i might just have to hual off and fix it but it would be nice to save a buck or 2.

RED-85-Z51

My valve doesnt close all the way, so it always leaks hot coolant through the core...so my A/C was not blowing hot air. So I took the hoses off and made a U bend between the hoses going to the core, keeping coolant out of the core, and thusly my A/C got colder.

If the valve is working properly, the in-hose on the core should not get hot when thre A/C is on.

You can see the valve work as you change the A/C settings.

zog

My valve is bad, so I don't get any heat...rather than spend the $$$, I simply wire the valve open in the winter and closed in the summer....takes 3 minutes...

SunCr

Depends on year - later model C4's don't have the valve and for those years, coolant is flowing to the core at all times providing marginal, but some additional cooling to the coolant.

Sometimes you can feel the inlet and outlet hoses or put a digital thermometer on them to verify flow. Problem is, a plugged core still flows coolant - it justs flows over the top, but not through it.

With or without the valve, air flow to the core is controlled by a door mounted in the heater box plenum. For manual air, it's controlled by a cable connected to the control panel. For electronic, it's controlled by an electric motor. You can view the door and verify it's operation by removing the resistor pod (manual air) or blower module (electronic air) mounted on the evaporator housing inside the engine compartment. Once removed, look inside the box and see if the door is moving while someone operates the controls.