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I have a 1971 BB w/AC. I have no heat. I have checked cable underneath console that controls the temp. and it is connected. I am going to change the heater control valve that is located behind front right tire. If this does not work, any other suggestions?
Have you checked the temperature of the hoses going to the heater core? Are they both hot when the engine is warmed up? I know of one case where a leaking heater core was "repaired" by placing ball bearings in the heater hoses.
It is also possible for the heater core or the control valve to become blocked by aggressive application of coolant system sealing products. Try to flush the heater circuit before any disassembly. That is, disconnect the heater hoses from the engine and try to flush water through the heater. Don't over do it -- the heater is good for about 15 psi. Some water systems can have more than double that pressure in them. If the water doesn't come out the other hose, when put in one hose, don't clamp the heater hose tight to the garden hose.
If the flushing fails, the control valve would be the next suspect.
Since your car has A/C, it should also have an in-line hot water shut-off valve that's controlled by vacuum and the setting of the cockpit's heater control circuit. The 'default' for the shut-off valve is to be open, meaning absent vacuum feed to the valve, hot engine coolant will flow to/through the heater core.
Some prior owners became frustrated with this setup because once the engine was warm and the car shut down for a short period (gas up, get lunch, Etc.), the hot water shut-off valve would open and the heater core would warm by natural convection action. Then, when the car was re-started and you drove away, hot air would 'leak' out of the interior air box (annoying).
There were two ways to defeat this 'idiosyncrasy' for summer driving: (1) learn to run the A/C in MAX mode for a short period of time after an engine restart episode to 'suck' heat out of the heater core, or (2) defeat the heater core altogether in the summer by either 'splicing in' a manual hot water cut-off valve OR plugging the hot water line to the heater core with something like a ball bearing as Terry mentioned.
Ergo, Terry's advice to get the engine warm and 'probe' the coolant lines to the heater core with your hands looking for a hot/cool junction along the way (approximate point where a prior owner plugged the line) is EXCELLENT advice! One piece of caution here:
DO NOT pull/tug on the hoses where they connect to the heater core's inlet/outlet nipples on the firewall!!!! The inlet/outlet nipples travel a fair distance from their firewall entry/exit points up to the top of the heater core and they're crimp-fit into the heater core. When you tug/pull on the hoses to get them off the nipples, the nipples serve as a SIGNIFICANT moment arm and more than one owner has generated problems (heater core leak) by rupturing the inlet/outlet nipple's crimp-fit to the heater core this way!
Chevy service manuals teach technicians to use a razor blade and carefully cut the hoses off the heater core's inlet/outlet nipples when doing service to prevent generating rupture leaks from excessive moment arm force (effectively shortening the hoses each time they have to be removed). Follow this advice and you should be OK. Accidentally TUG on a heater hose line, break the inlet/outlet nipple junction at the heater core, and you're in for a MAJOR effort to R&R the heater core!
Having a 70 with the same air conditioning and heating system as your BB, the only time coolant is not flowing through the heater core is when you select MAX cooling. When MAX cooling is selected vacuum is applied the the valve you mentioned. If you are going to replace the valve I have found it is very easy to remove the vent grille on the fender and have ample work area. If you do this, don't remove the screws untill you remove the 7/16 nut from the bottom, once you learn where the 7/16 nut is, you will be able to just sit beside the car to remove it with a 1/4 inch extension, 7/16 socket, and ratchet. It is a special configured nut with washer attached. Remove the two screws and lift carefully.
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