> For the complete documentation index, see [llms.txt](https://hrftank.gitbook.io/hrftank/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hrftank.gitbook.io/hrftank/iii-build-manual-electronics/12.-water-cooling/12.4-water-cooling-assembly.md). # 12.4 Water cooling assembly {% stepper %} {% step %} ### Assemble the pump module Prepare the pump by soldering wires with connectors to its leads (I chose JST-RCY, male connector).\ Mount two pieces of silicone tubing onto the pump – 10 cm on the middle outlet and 8 cm on the “outer” outlet – and secure them with zip tie at the marked spot.\ I’m not sure if a zip tie installed like this will actually help, but I want to believe it’s better than nothing...
Place the pump in the holder so that the “outer” outlet faces upward and the front of the pump is flush with the clamp. Secure the pump with one M3x30 screw (x1)
In the lower cover of the coolant reservoir, mount: * a temperature sensor with G1/4 thread * a 90-degree adapter and a barbed fitting
In the upper cover, mount the bubbler from the inside.
Mount the water reservoir on the upper part of the pump holder, so that the fitting is facing the front of the tank, and the angled connector is to the right of the temperature sensor.\ If the reservoir is too loose and rotates, you may need an additional gasket printed from TPU (PETG in a pinch), 55x51 mm.
Join both halves of the pump holder with M3x8 screws (x4).\ Secure the silicone tube on the barbed fitting with a zip tie.
To protect the motor leads from damage, secure the wires to the mount with another zip tie.
{% endstep %} {% step %} ### Install the radiator Install two barbed connectors in the radiator and place it in the hull so that the fittings are on the left side of the tank.
Using M3x8 screws (x4), first mount the bracket on the right side, then on the left.
### Install the fans {% endstep %} {% step %} Prepare the appropriate connectors on the fans (e.g., JST-RCY, male connectors, 2 pieces).
Using the screws included with the radiator (#6-32, 31 mm), mount the fans along with their guards.\ Pay attention to orientation! Airflow should be directed toward the radiator.
{% endstep %} {% step %} ### Install the motor temperature sensors {% hint style="warning" %} Before placing the DS18B20 sensors into the housings, take any servo wire and check if the connector fits its holder.\ After mounting the sensor, check again whether the sensor leads fit the servo connector and, if necessary, adjust them {% endhint %} Place the DS18B20 sensors in their housings – insert the leads into the slots, and press the sensor body into the recess, with the flat side facing upward.
Slide the covers onto the motors and secure them with zip ties.
{% endstep %} {% step %} ### Install and connect the pump module Place the pump assembly in the hull and fasten it with M4x12 screws (x2) and M4x30 screws (x2).
Connect the hoses to the cooling jackets of both motors as shown in the pictures. The hose connecting the left motor to the radiator should be at least 23 cm long – otherwise, removing the left gearbox cover will be nearly impossible.
Secure the hoses with zip ties (x5).
{% endstep %} {% step %} ### Install the reservoir inlet connectors Prepare the following: * 90-degree adapter and exhaust valve * four-way adapter, male-to-male adapter and end plug * barbed fitting
Mount the four-way adapter with male-to-male adapter and end plug onto the upper inlet of the coolant reservoir.
Attach the 90-degree adapter with the exhaust valve and the barbed fitting.
Connect the silicone tubing to the radiator fitting and the barbed fitting. Secure it with zip ties.
{% endstep %} {% step %} ### Prepare the multi-core wire for the cooling system You will need the following connectors: * 2x 2-pin for the radiator fans * 1x 2-pin for the coolant pump * 2x 3-pin for the engine temperature sensors * 2x 1-pin for the engine temperature sensor
{% hint style="info" %} The radiator fans will operate simultaneously — you can connect them in parallel, using a single common connector on the electronics compartment side. The coolant sensor with a ¼" thread is a simple thermistor — pin order does not matter. Pay close attention to the pin connections of the DS18B20 sensors! The housings are marked with (+) and (–). **Reversing the connection will burn the sensor!** {% endhint %} Install the cable into the rear bulkhead.
{% endstep %} {% step %} ### **Fill the cooling system** Remove the end plug and attach the barbed fitting with approximately 15 cm of silicone tubing. Optionally, remove the exhaust valve and raise it by attaching a male-to-female adapter to a 90-degree adapter. Connect a 12 V power source to the pump, but **do not turn it on yet**. Running the pump dry may damage it.
Prepare approximately 200 ml of cooling liquid (PC coolant or distilled water). With a syringe attached to the silicone tubing, inject the first portion of cooling liquid (approximately 20 ml) into the system. Then **turn on the pump** and attach a syringe filled with the next portion of liquid.\ Press the exhaust valve to release pressure (**beware of splashing water** and protect the electronics). After that, inject the next portion of cooling liquid.
{% hint style="warning" %} Remember to disconnect the syringe from the tubing only after releasing the pressure using the exhaust valve. Otherwise, you may get a jet of water.\ To reduce splashing, you can press the exhaust valve using a hand towel. {% endhint %} After injecting about 100–120 ml of cooling liquid, you may create overpressure in the cooling circuit. A sign of this is a change in the pump's operating sound.\ While maintaining slight overpressure, visually check the circuit for leaks. If there is no visible leakage and the syringe plunger does not move back under pressure, the circuit is sealed.\ When you hear that the pump is working under higher resistance (a different sound), stop injecting liquid, press the exhaust valve, withdraw about 5 ml of liquid, and press the exhaust valve again.
Run the system for 1–2 minutes, until you no longer see or hear air bubbles in the tubing. Check the level of cooling liquid in the reservoir. For better pressure stability, there should be some air left in the tank. A gap of about 1 cm between the liquid level and the tank lid should be sufficient. If there is too much or too little liquid, add or remove it accordingly.
{% endstep %} {% step %} ### Connect all connectors Connect: * the pump connector * the two radiator fan connectors * the cooling liquid temperature sensor connector * the two motor temperature sensor connectors (**observe correct polarity**)
Then connect the connectors at the other end of the multi-core cable to the power and control system (HRF Main PCB or your own design).
The cooling system is now ready for operation :wink: {% endstep %} {% endstepper %}