How old refrigerators are designed and work: from the compressor to the thermostat

Old refrigerators are real long-livers that still serve well in many homes. Unlike modern models with electronic panels and inverter compressors, equipment from the 70s, 80s and even 90s works according to fundamentally different schemes. Their design is simpler, but no less effective if you understand how they function.

In this article we will look in detail at how refrigerators of Soviet brands (ZIL, Minsk, Biryusa, Orsk) and early foreign models (Indesit, Ardo, Snaige) are designed. You will learn which components are responsible for cooling, why old units hum so loudly, how the refrigerant circulates, and what to do if the refrigerator stops freezing. And also - how to safely operate equipment that is already several decades old.

Main components and principle of operation

Any refrigerator, regardless of the year of manufacture, works according to one physical principle: heat removal from the interior to the outside. In older models, this process is organized using four key elements:

• 🔧 Compressor —the “heart” of the system, which pumps refrigerant through the tubes.
• ❄️ Evaporator —a metal grill inside the chamber where freon boils and takes away heat.
• 🔥 Condenser —a coil on the back wall that releases heat to the environment.
• 📉 Thermoregulator (or thermostat)—a sensor that turns the compressor on and off as needed.

The cycle begins with the compressor compressing the gaseous refrigerant (in older models this is most often R-12 or R-22) and directs it to the condenser. There the freon cools, turns into a liquid state and enters capillary tube a thin channel where the pressure drops sharply. The refrigerant then enters the evaporator, where it turns back into gas, absorbing heat from the chamber. The process is repeated until the thermostat registers the desired temperature and turns off the compressor.

Unlike modern refrigerators, which use isobutane (R-600a) or mixtures based R-134a, old refrigerants were less environmentally friendly, but more resistant to leaks. For example, R-12 could circulate in the system for years without topping up, if there was no mechanical damage to the tubes.

Compressor: why it hums and how it works

The compressor in old refrigerators is an electromechanical piston-type device that operates on the principle of a pump. Its main parts:

• 🔌 Electric motor - rotates the shaft connected to the piston.
• ⚙️ Piston group - compresses the refrigerant and pushes it further through the system.
• 🛢️ Oil sump - provides lubrication of rubbing parts (mineral oil was used in older models).
• 🔊 Spring shock absorbers - dampen vibrations (their wear often causes increased noise).

Loud operation of the compressor is the norm for equipment 20+ years old. Causes of noise:

1. Natural wear of bearings and piston group.
2. Loose fastenings of the compressor to the refrigerator frame.
3. Oil contamination with wear products (in this case the hum becomes more hoarse).

If the refrigerator suddenly starts working louder than usual, check:

Make sure that the refrigerator is level (adjust the legs)

Check if the compressor is touching the back wall or tubes

Clean the condenser from dust (it is located at the back)

Listen for any extraneous knocking (they may indicate valve failure) -->

In old refrigerators, the compressor can work for up to 30–40 years without replacement, if it is not overloaded and the condenser is kept clean. However, over time, its power decreases, and the refrigerator begins to freeze worse. In this case, diagnostics of the pressure in the system or replacement of the refrigerant is required.

Refrigerant and oils: what is filled in old models

In refrigerators, those produced before the 2000s used refrigerants that are today considered obsolete or even prohibited (for example, R-12 due to harm to the ozone layer). Here are the substances that could be in your unit:

If there is a freon leak in your refrigerator, you cannot simply add new refrigerant - you need to take into account compatibility with oil. For example, if the system is designed for R-12, and you fill R-134a, the compressor may fail. building due to incompatibility of oils. In such cases, a complete flushing of the system is required.

⚠️ Attention: Refrigerants R-12 and R-22 are toxic if leaked in a closed room. If you smell a chemical odor or notice oily stains on the floor, immediately ventilate the room and turn off the refrigerator.

Thermoregulator: how it controls the temperature

In old refrigerators, a device that opens the electrical circuit of the compressor when the desired level of cooling is achieved is responsible for maintaining the set temperature. Its operating principle is based on the properties of gases or bimetallic ones. plates: mechanical thermostat - a device that opens the electrical circuit of the compressor when the desired level of cooling is reached. Its operating principle is based on the properties of gases or bimetallic plates:

1. Inside the thermostat there is bellows a corrugated tube filled with gas (for example, chloromethane).
2. When the temperature drops in in the chamber, the gas is compressed and the bellows contracts, opening the contacts.
3. When the temperature rises, the gas expands, the contacts close, and the compressor turns on again.

Typical malfunctions of the thermostat:

• 🔌 Sticking contacts — the compressor works without stopping, the refrigerator freezes.
• ❄️ Gas leak from the bellows —the thermostat does not respond to temperature, the compressor does not turn on.
• 🔧 Oxidation of terminals —periodic malfunctions (the refrigerator turns on and then no).

You can check the thermostat yourself:

1. Disconnect the refrigerator from the mains.
2. Remove the temperature control knob (usually it is attached to a latch or screw).
3. Under the handle there is a screw for setting - try turning it half a turn clockwise (this will increase sensitivity).
4. If after this the compressor started working, the problem was in the setting. If not, the thermostat needs to be replaced.

Evaporator and defrosting system

The evaporator in old refrigerators is a metal radiator, usually located on the back wall of the freezer or refrigerator compartment. Unlike systems No Frostwhere ice is removed automatically, Soviet and early foreign models use drip defrosting or manual.

How it happens cooling:

1. The refrigerant enters the evaporator under low pressure and begins to boil, taking away heat.
2. Frost forms on the surface of the evaporator, which turns into ice over time.
3. When the compressor is turned off, the evaporator temperature rises, and the ice melts - the water drains into the pan (in models with a drip system).

Problems associated with the evaporator:

• ☃️ "Snow coat" — a thick layer of ice on the walls due to a faulty thermostat or door seal.
• 💧 Water leaks — the drainage hole is clogged or the pan is cracked.
• 🔥 Compressor overheating - if the evaporator is covered with ice, the refrigerant cannot circulate normally.

To defrost an old refrigerator correct:

Unplug the refrigerator and remove all food

Install a tray to collect water (in Soviet models it is often missing)

Do not use a hairdryer or hot water - this may damage the seal

After defrosting, wipe the chamber with a weak solution soda (1 tablespoon per 1 liter of water)-->

⚠️ Attention: In refrigerators with manual defrosting (ZIL-63, Minsk-16), you should not chip off the ice with a knife or fork - this can pierce the evaporator and cause a freon leak.

Electrical circuit: why old refrigerators are more reliable

One of the main advantages of old refrigerators is the simplicity of their electrical circuit. In most models, it consists of only a few elements:

• 🔌 Power cord with plug —often non-separable, with grounding (in Soviet models, grounding was connected to a metal case).
• 🔄 Start-protection relay —starts the compressor and protects it from overloads.
• 📡 Thermoregulator —controls the compressor on/off.
• 💡 Lighting lamp —turns on when the door is opened (in older models this is a regular 15-25 W incandescent lamp).

For comparison: in modern refrigerators with No Frost electronically controlled circuits include dozens of components - control boards, sensors, fans, defrost heaters. This increases the risk of breakdowns. In older models, there is practically nothing to break, except:

• 🔌 Burnt contacts in the start relay (cleaned with sandpaper).
• 🔧 Burnt spirals in the thermostat (requires replacement).
• 💡 Oxidized wires (especially in soldering areas).

If the refrigerator stops turning on, check:

1. Voltage in the socket (should be 220–230 V).
2. Integrity of the power cord (often frays at the base of the plug).
3. Starting relay - when shaken it should not rattle (this is a sign of breakdown).

How to ring a compressor with a multimeter?

To check the windings compressor, disconnect it from the relay and ring the contacts:

- The resistance between C (common) and S (starting winding) should be ~20–40 Ohm.

- Between C and R (working winding) — ~10–20 Ohm.

- Between S and R is the sum of the two previous values (~30–60 Ohms).

If at least one value is 0 or ∞, the compressor is faulty.

Typical breakdowns and how to avoid them

Despite their reliability, old refrigerators begin to act up over time. Here are the most common problems and their causes:

To extend the life of the refrigerator, keep an eye on:

• 🧊 Cleanliness of the condenser - dust and cobwebs impair heat transfer, causing the compressor to overheat.
• 🚪 The condition of the seal - if the rubber is cracked, it needs to be lubricated with silicone grease or replace.
• ⚡ Voltage stability - surges in the network can burn the compressor winding (use a stabilizer).

⚠️ Attention: In refrigerators older than 30 years there may be asbestos insulation in doors or rear panel. When making repairs, do not disassemble these parts yourself - contact a specialist with protection.

FAQ: Frequently asked questions about old refrigerators

Is it possible to replace R-12 freon with R-134a in an old refrigerator?

Theoretically yes, but it will be necessary:

1. Complete flushing of the system from old oil (mineral is incompatible with R-134a).
2. Replacing the filter drier.
3. Refilling with polyester oil (POE).

However, in practice, such a replacement is often unjustified - it is cheaper to buy a new refrigerator. In addition, R-134a is less efficient in older systems, and the compressor will work with increased load.

Why does an old refrigerator freeze less than before?

There are several reasons:

• Natural wear of the compressor (discharge pressure decreases).
• Freon leakage through microcracks in the tubes.
• Clogged capillary tube (due to moisture or oil decomposition products).
• Thermostat malfunction (incorrect triggered to turn on).

For diagnostics, you need to check the pressure in the system and test the compressor. If it is still “alive,” sometimes refilling freon helps.

What is the service life of a Soviet refrigerator?

With proper operation:

• ZIL, Minsk, Orsk — 25–40 years.
• Biryusa (models of the 80–90s) - 20–30 years.
• Foreign brands (Indesit, Ardo) - 15–25 years.

Record holders are refrigerators ZIL-62 and Minsk-15which are still have been working since the 70s. The main thing is to defrost regularly and not overload the compressor.

Is it possible to put an old refrigerator on the balcony in winter?

No, if the temperature is below +5°C. In cold weather:

• The oil in the compressor thickens and it may not start.
• The thermostat will not work correctly (designed for positive temperatures).
• The door seal will lose elasticity and crack.

If you need a refrigerator to store food in winter, use a model with climate class SN-T (designed to operate up to +10°C).

What to do if the refrigerator is electrocuted?

Reasons and solutions:

• 🔌 Breakage to the housing —compressor or wire malfunction. Immediately unplug the refrigerator! Replacement of the damaged unit is required.
• ⚡ Lack of grounding —connect refrigerator through an RCD or socket with grounding.
• 💧 Moisture inside —dry the chamber, check the seal.

Operating a refrigerator that "pinches" is dangerous - this can lead to injury electric shock.