How do i replace the heater control valve in a 1998 chev.c1500 v6 pu

Either your heater control valve is not properly operating or your heater core is clogged. Locate the heater control valve under the hood, should be close to firewall on heater hose, have someone adjust temperature from hot to cold and see if you can see the heater control valve operating if so replace the heater core, if its not doing anything replace it(heater control valve).

the thermostat is either stuck open or the heater core is clogged

The right side hose coming from heater core runs into a connector. There is a hose parallel to this connector. At the end is what your looking for. If your wanting to replace this cause your heater doesnt work id recommend flushing your heater core first. My heat didnt work at all flushed it yesturday and works like a charm.

there is a vacuum switch inline on the heater hose that is not opening up and letting the hot water go into the heater core.
replace the heater control valve on the heater hose coming from the water pump.

before you think it is your heater core try replacing your thermostat or flushing your system your heater core could be clogged feel the two hoses going into the heater core at the firewall they both should be hot

Check the heater hoses going into the heater core.Both of the hoses should be hot to touch,when the engine is at normal warm running conditions.If only one,or none of the two hoses are not hot,or very warm.then pull the heater hoses off,and use a water hose to flush the heater core out.Make sure the coolant level is full,if it is not,then the heater core will not get coolant flow threw it.

Sounds like a stuck heater core valve. Find heater core valve. Under hood, find the two heater core hoses going into firewall. One of the hoses has a valve. Operate temperature control (full heat, then full cold) check that valve changes position. If not either replace valve or control system failure. Also, when temperature control in cold position, one hose should feel hot and the other cold. Temp fix: disable valve to close no heat or on heat.

There are 2 hoses going through the firewall from the engine, these are the coolant hoses to the heater core, one is 3/4" and one 5/8", the control valve should be in the larger line (3/4") which is the inlet, make sure that the valve has vacuum (heater on low), also check and see if both hoses get hot with the heater blower on low, if they do get hot your problem is not the heater control valve but the air temp control blend door actuator.

The hoses from your heater core should be very hot to the touch. Check the hoses going to the core from the water pump. It should be very hot. The return hose should also be very hot. Now check the hoses going to the core. If they are not the same temp, then your heater control valve is not working correctly or the vacuum is not working. At any rate, locate the vacuum line going to the heater valve. Remove the silver bar on the valve from the plastic plunger arm. You will have heat all the time now if it was only a vacuum problem. You can fix it later when it's warmer out. BTW a 200* thermostat will make your heater even hotter.

Follow these steps:

Check coolant level, then start engine until it is warm and the thermostat opens. You will tell when it does when the needle on your temp gauge goes cold when it reaches around 180-200* and then goes back up. Now turn on your heater full blast and go to the engine compartment. You will see a heater valve located on the passenger side, next to the washer reservoir. It is a black thing with 4 heater hoses connected to it. Feel the hoses. When everything is working correctly it should be like this:

Hose going to waterpump will be hot
Hose going to (I think the thermostat housing) will be hot
2 Hoses going to heater core (mounted behind firewall) will be hot

1. If only 1 heater core hose is hot, heater core is clogged--
UNCLOG: remove 2 hoses going to heater core when engine is cool, hook water hose end to one of the sides and flush out gunk from heater core. Reconnect hose and you should be good.

2. If neither hose core hose is hot, heater control valve is bad or vacuum is bad--
Test Vacuum: remove vacuum line from heater control valve, you should feel the vacuum **** on it when pressed to your cheek and the heater control valve actuator should move when you unhook the vacuum line. If you have a good vacuum, it's probable the valve available at autozone part # 5941 for around $21.

To get heat while you wait to replace part, unhook silver arm on heater control valve that is hooked to the plunger. This will give you heat all of the time, but it is controlled by the bottom hot/cold switch on your heater control unit so you won't get hot in the cab. It will just circulate heat through the core.