Heater Problems

The heater in my friends '90 does not heat up, no matter what the temp setting. Ideas?
THX

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Pappy wrote:

I'm not familiar with the Corvettes in that series, but in general for most cars there is a valve somewhere under the hood inserted in the smaller (1"?) hoses that go from the engine water pump to the heater radiator core and back (through the firewall) to the front of the engine. The valve is usually smaller than the palm of your hand, and probably has 3 hoses attached to it. It may be electrically or vacuum operated. It's job is to allow engine coolant to pass through a small heater radiator under the dash when heat is called for, or divert it right back to the engine via the heater return hose if no cabin heat is needed, so if it sticks closed, or if it's electrical or vacuum signal is disrupted (electrical short, vacuum leak, corroded connection, malfunctioning cockpit control, blown fuse, etc) while it's closed, it will not open when the driver activates the heater controls. Often these valves stick closed during the long summer of dis-use. The valve usually isn't very expensive to replace.
There are other possibilities, of course:
- the heater controls in the dash are malfunctioning and not sending a signal to that valve, which is more difficult to fix.
- the hot engine coolant is flowing in the heater core, but the heater blower motor is not operating at all (generally your ears tell you the blower is/isn't working, or your suddenly colder feet tell you it is); ie, bad motor or it's not getting electricity or has a bad ground connection.
- the air vents that direct air through the blower motor and heater core or to the dash and feet vents are not opening in response to the settings the driver made (the dash heater controls, or the vent-actuating solenoids somewhere under the dash are bad).
Start with the diverter valve in the engine compartment.
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Pappy wrote:

Manual AC/Heating controls or electronic climate control?? PJ
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Have you ruled out the thermostat?
That seems like one of the first things to check, just thought I'd toss it out there.... :-)
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The car can be driven for an hour, and the air does not get warm at all. You can hear a "clunk" when you turn the heat on, and the fan blows cool air...
:-(

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Pappy wrote:

The "clunk" is almost certainly the air vent doors being actuated, and the cool air blowing indicates the fan is working, so find and check out the bypass valve on the heater hoses that I mentioned in my prior post... older cars used to have that valve under the dash, manually operated, but since the late 60's it's been in the engine compartment and remotely operated.
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Steve wrote:

That's a good question.. What is the engine temp? Is the engine getting to full operating temp?
Dennis
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I'd like to hear something on this also. My '94 doesn't get hot either. It runs around 190-200f. It gets luke warm but not hot. I seeing that it gets luke warm I'd figure that the door is moving. I wonder if there is a heater hose shut off valve under the hood? Guess I better break out the service manual and see if there is a flow chart for this problem.
Pappy wrote:

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Ric Seyler
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It could also be a "clog" in the heater core. If your engine is running a full temp, then either the air is not being completely directed through the heater core or the heater core is not flowing any hot water (valve, clog, ect...)
RicSeyler wrote:

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My first plan of attack will be searching for a underhood valve, cuz I'm not looking forward crawling under that dash and removing all the panels to get access. I get dizzy now-a-days when I'm upside down under a dash.... Old age I guess ;-)
Dennis Willson wrote:

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