Heater Control Valve (HCV)

I started working on the heating and the cooling system. The first step was to make a diagram to ensure that I understood how everything was connected.

I keep stumbling into little things that are different with a mid-engine car and I found another one. In a front engine car, the engine (the heating source) and the heater core are very close to each other. In a mid-engine car, the cockpit is between the two. Since it's important to keep the cockpit cool, the last thing I want to do is pump hot water from the engine, through the passenger side of the car, into the heater core under the dash and then have if flow back unused. To prevent this from happening an electric heater control valve (HCV) is installed in the tail section. However, it has been reported that the LS engine can overheat if you start your engine with the A/C on and you have a heater control valve that simply closes the water pump's heater outlet. In other words, LS engines need a constant loop of coolant flowing through the water pump's heater outlet.

To solve this issue, several other builders have used this heater control valve made by Old Air Products which allows coolant to flow even when the heater is turned off. The business end has four 5/8" hose barbs and a valve. Connected to the valve is a servo which is wired to a separate servo controller which is in turn wired to a potentiometer. This provides continuous adjustment from closed to fully open. There are five wires (two for power and three for the position feedback potentiometer) so it's a closed loop control system.

A quick search on the name on the actuator turned this Voltage Control Actuator from Newbase, a Chinese company. The only moderately useful information on that site is the pin out and that it draws a whopping max 300 mA. There is a dimensioned drawing of the locations of the screws that attach the actuator to the valve. Well, the drawings are wrong... I get that it's hard to translate from Chinese to English, but the dimensions were in millimeters!

I considered controlling the HCV via MoTeC by replacing the potentiometer with a digital potentiometer controlled by an Arduino which would then be interfaced to the MoTeC. It would work, but it's a fair amount of work, introduces a bunch of things that might break and I don't really gain anything... nah, not worth doing.

The HCV is awkwardly shaped and there is no easy way to mount it. While pondering the best way to mount it I noticed that the actuator fit perfectly in a triangular dead space in the 2" x 6" chassis. I then realized that I could remove the three screws and and spacers connecting the actuator to the valve and sandwich an aluminum bracket and replace the spacers with shorter ones... OR I could just print a panel large enough to seal the hole (something that was on my to do list) and mount both the motor controller and wire connector. 

The panel is sandwiched between the valve and actuator, thus replacing the standoffs. It was made large enough to cover the hole and mount the motor controller and a new wire connector. There wasn't a way to mount the motor controller so I simply drilled the cover plate mounting holes all of the way through and used stainless 4-40 screws and nylocs. Since heat rises, I decided to print a heat shield between the heater lines and the motor controller and to put Reflect-a-GOLD (aka TRUMP TAPE) on it. I cut 80% of the harness off and terminated one end into a Deutsch connector. I removed the connector to the actuator, fed the wire through a vinyl grommet and re-terminated it on the back side. Since I couldn't figure out what type crimp connectors were used I carefully cut the old ones out of the harness and soldered them on. Everything now fits on one tidy panel!