Common Issues with Car Heating System and Solutions

Important heating problems (not blowing air, cold air, weak airflow)
1— The fan motor for low speed settings (LO button) doesn't work.
The issue in 100% of cases is in the thermistor. It's located behind the lower shelf below the glove compartment. To access it, remove the shelf, disconnect the connector, unscrew two screws and take out the thermistor itself. Here's how it looks:

1 of 2

Solution: each setting is controlled by a spiral, and the low-speed spiral is the thinnest, thus burning out quickly. Unfortunately, soldering with an ordinary soldering iron is not possible, so go to a vape shop (or get one from a 'Zhiguli') and buy nichrome wire of the same resistance, wind it up into a similar spiral and find a way to attach it (solder, press, insert, or something else).
You can order a new thermistor! At the time of writing this article on Exist its price is approximately 1500 rubles. (part number: 88635-22041), but delivery takes almost a month.

— Weak airflow even at maximum speed and/or cold air.
Solution: usually, this happens due to a clogged evaporator of the AC unit. It's located right between the fan motor and the heater radiator, so when it’s dirty, air simply doesn't reach the radiator and duct system, causing weak and cold airflow. Cleaning the evaporator is quite laborious as it involves removing it along with the shelf and glove compartment, then unscrewing all relevant hoses under the hood (the hardest part). There's a slightly less effective but more convenient way to clean inside using hand/ vacuum/shoefun hose after removing only the fan motor.
Don't forget that before freezing fingers typing queries about cold air in your car online, check coolant level and ensure your heater radiator is not too old or damaged. Also make sure the heater valve (found on the cowl—round vacuum actuator with a lever) is open.

— The heating system suddenly blows cold air at certain RPMs.
In 71 model cars with climate control versions (most vehicles), all heater controls are operated by vacuum actuators! If any hose bursts/tears/off, it may lead to sudden changes in the behavior of the HVAC without obvious reasons. Pipe/shark schematics can be found on epcdata.ru. If all other heating system components are fine (see above), then you need to check the actuator left of the clutch/handbrake pedal; it should move up/down and push the lever directing air through the heater radiator or around. If it works, see if the lever has slipped off its track behind the radio—it connects to the valve on the passenger side near the footrests. Also under the hood, close to the heater valve, there's a vacuum actuator control box as a square box with hoses attached; they should be correctly connected or else the system won't work properly.The connection diagram of these tubes is fixed on a video. Stay warm!.
Не мерзнете!