grayml

Hello everyone,

Sorry if I seem ignorant, but the heater control valve that is inline with one of the heater hoses seems to be useless. It appears to me to be no more than a piece of plastic pipe, I just do not see how it can control anything heat wise. How exactly does this work being a passive device with no valve to control water flow?

I just installed a new one, the water flow is correct based on the arrow indicator on the unit but I still have little heat. The heater core is new, I flushed it before installation to make sure of no blockages, and the radiator and hoses are new as well. Vent doors appear to be working properly as well. Engine temps are normal, 205-210.

Any ideas?

VenkmanP

I don't know the answer, but you probably need to specify if you have manual or electronic HVAC controls.

A picture of the valve in question might help also.

vettenut94

grayml, just a thought but did you bleed all the air from the system? and is the over flow bottle down by the r/f headlight filled to the max mark?

RAGOVET

i did not think the 94-96 years actually had a heater control valve. there is some other mechanism for regulating heat.

rayosequis

Does your cruise control work ? My AC was acting up, and the vacum lines running the cruise control were leaking and the AC malfuntioned as well.

williammackean

(Puts Dunce Cap On)

Bleed the system? I was under the impression that air will naturally vent thru the overflow tube as one reached normal operating temperature. Could this explain the hit-&-miss heat I get from my manually-controlled '85? or is this more of a controller problem?

How does one 'bleed' this system? (I'll need to know for when I do the TB bypass.)

This would explain why I always get a 'Lo' reading on my dash display, yes?

Throw a newbie a bone! Thanks!

Morley

The heater control valve is operated by vacuum ported to it from the climate controls. When heat is not selected the valve is ported so that the coolant just runs in a loop, bypassing the heater core. When heat is selected, the valve is then ported so that coolant will pass through the heater core.

grayml

Manual. I'll get a photo also.

grayml

Yes, bled the system and it is full.

USCG

That part (picture attached if my computer skills are working today) is a "flow control" device. The arrow points to the heater core, and it limits the flow to the heater core during high revs, thereby protecting the heater core from bursting from high pressure.

Oops, I cant post attachments....sorry.

grayml

I'm trying to find the box that the part came in, but it is labeled as a heater control valve. As soon as I do find it I'll post the part number.

grayml

Yes, the cruise & AC are fine.

grayml

Is this in the engine compartment or the dash? I've looked under the hood and I don't see any vacuum fittings anywhere near the heater core area.

grayml

AH HA!!! So now I know.

VenkmanP

Since you have manual HVAC, I don't think the vacuum issue applies.

Looking at the shop manual, it looks like the only things involved are the temperature door/cable and the heater core.

So I'd guess either the cable/door is misadjusted or the heater core is plugged.

For the cable adjustment, the manual says you should be able to hear a distinct click at the two extreme ends of travel.

For the heater core, the manual says:
- check coolant level
- run engine to normal operating temp
- set temp lever to full hot
- set blower on high
- select any mode except off
- place hand near upper and lower heater core hoses (not on hose - hot). Upper hose should be cooler. If both hoses are about the same temp you have a blockage.

theadmiral94

Was Valve Part # AC/Delco 15-5423/GM # 10157988? If so, then you installed the correct part and as already mentioned, all it does is restrict the flow to the heater core so as to reduce the pressure to the heater core.

As also mentioned, there is no open/close/bypass 'heater valve' on the 94's, the cabin heat is controlled by a 'door' that directs or blocks the hot air.

Simple test. is the heater core inflow radiator hose & the outflow small 180 degree turned radiator hose both hot? If so, it may be all inside with the heater controls as mentioned by others, if not, read on...

Have you checked the 'pressure' (radiator) cap on the 'surge tank' to assure it is holding pressure? if it's been replaced, was it with a quality unit and the Correct unit (read reports that many do not hold pressure as marketed, AC/Delco # RC27 is the correct one for our 94's and some are selling the wrong one for our car -- e.g. Ecklers)?

Is the 'air bubble' maintained within the 'surge tank' (did not overfill the surge tank, level should be 'just' up to the bottom of the lower lip where the radiator cap lower gasket contacts -- the air bubble is important for air is compressible and is needed to move air through the system)?

Was the two bleeders opened to removed air from the cooling system (with rags/paper towels below to save your opti-spark)? one is on the thermostat housing, the other is on the passenger side, just above where the upper radiator hose connects to the engine.

Might the 'air bleed' hoses be blocked? There is one to the radiator passenger side, and one to the back of the heads, 'jumpering' between both passenger then driver rear side head. You should be able to see some outflow into the 'surge tank' via the 2nd hose that connects below
the 'radiator cap' area.

Is the thermostat the special AC/Delco thermostat (#131-100 or GM # 12555290), with the extra plate on the bottom to close-off the water-pump bypass 'circuit' when it opens (not sure, but engine temp might run ok with a thermostat that doesn't have the extra plate, but without the plate it might cause your problem -- however, be careful if checking to not dump anti-freeze on your opti-spark distributor beneath)?

Have you been able to confirm water flow into the 'surge tank' from the heater core? The normal flow direction is from the water pump lower passenger side 'bypass' metal pipe, through the heater hose with the the 'valve/reducer' you replaced therein, on to the heater core, and then from the heater core via a short almost 180 degree hose to the bottom of the 'surge tank.

pablocruise

I don't think there were heater valves put on our cars after 87.

Grayml, since you said you replaced the H/C, sounds like you have been in there pretty good, but lemme ask anyway: Can you verify the blend door is moving to the diver's side?
It's pretty common to lose vacuum in the HVAC system from old cracked brittle vac line under the injector cover.

USCG

Is that the "Blend" door that we are looking at? I have a 96 manual HVAC and will be going after that door as my next project. Seems that the air coming from the vents is 15 degrees hotter than outside air temp. That blend door is supposed to close off the air to the heater core in the full "cold" position. I think my door may not be closing completely. I've checked it after 15 minutes at highway speeds. The Helm manual directs me to the control cable which I believe should be under the dash on the passenger side.

I replaced that flow control device about 6 months ago. I'll look up the part no and post it if I can find the receipt.

USCG

Does the part look like this?

http://www.artscorvetteparts.com/par...1-fa1325d3b894

Just a thought, but when I took my defective part out, I temporarily put in a 1/2" copper nipple that allowed full flow thru the core. Try that and see if your heat at low rpms improves. Might want to keep from overreving the motor with the copper nipple in there just in case that part really is needed.

http://www.artscorvetteparts.com/par...1-fa1325d3b894

Lichen

A new heater control valve completely solved my '93's heating problem. Maybe our terminology differs on some of these parts. I went 2 winters without any heat, but I live in AZ, so no big deal.