The refrigerator stopped freezing, and Is the compressor either humming without starting, or silent, although the light inside is on? In most cases, the culprit is thermostat or its actuator - the relay. It is this connection that is responsible for turning the motor on and off depending on the temperature inside the chambers. Understanding how to check the refrigerator thermostat relay allows you to save a significant amount on calling a technician and quickly bring the equipment back to life.
Diagnostics does not require complex industrial equipment. A basic set of tools and a multimeter are enough. It is important to understand that the malfunction may lie either in the sensor itself, which “does not sense” the cold, or in the contact group, which does not physically close the circuit. Modern models Electronic sensors are often used, but mechanical thermostats with relays are still widespread in everyday life.
In this article we will analyze the design of the unit, methods of checking with a multimeter, possible causes of failure and the procedure for action if a defect is detected. If, when testing with a multimeter in any position of the regulator knob, the circuit does not close, the part definitely requires replacement. Carefully follow the safety instructions, since the work is carried out with electric current.
Principle of operation and device node
The thermostat is a device that controls the temperature in the evaporator. Inside the sealed bellows tube is freon or other gas-filled mixture, which expands when heated and contracts when cooled. This movement is transmitted to the membrane, which opens or closes relay contacts. When the contacts are closed, current flows to the compressor starting relay, starting the motor.
The design can be single-contact or two-contact. In the first case, only the phase wire is opened, in the second - phase and neutral, which ensures a more reliable disconnection. Inside the case there is also spring mechanism, the tension of which is adjusted by turning the knob on the front panel. The tighter the spring is, the lower the temperature must drop for the contacts to open.
- 🔧 Bellows tube - a sensitive element that transmits gas pressure to the membrane.
- ⚡ Contact group - moving and fixed contacts that switch electrical circuit.
- 🔩 Adjusting screw —an element for setting the temperature range, hidden under the handle.
During long-term use, the contacts may burn, oxidize or stick. The spring may lose its properties, and the bellows may depressurize. In this case, the thermostat stops sending a signal to start the compressor, even if it is warm in the chamber, or, conversely, does not turn off the motor, leading to freezing products.
Visual diagnostics and preparation for testing
Before taking into hand a multimeter, it is necessary to conduct an external examination. Often the cause of failure lies in banal oxidation of contacts or mechanical damage to wires. Unplug the refrigerator! This is the first and main safety rule. Remove the temperature control knob and protective casing to gain access to the terminals.
Inspect the wires for melted insulation. If you see black spots or smell a burning smell, it means there was short circuit or a bad contact in the circuit that caused overheating. Carefully check the sensor tube itself: there should be no dents, cracks or signs of corrosion on it. Any violation of the tightness of the tube makes further diagnostics pointless - the thermostat is no longer working.
⚠️ Attention: If you find traces of plastic melting around the terminals, simply replacing the thermostat may not solve the problem. It is necessary to check the compressor starting relay and the condition of the wiring, since the cause of overheating could be in them.
Carefully remove the terminals from the thermostat contacts. Pay attention to their condition: if the metal is covered with a green coating or rust, sand them with fine-grained sandpaper before taking measurements. Poor contact at the connection point can distort the results diagnosis.
Necessary tools for diagnostics
For a high-quality test, you will need a minimum set of tools. The main device will be a multimeter (tester) configured to measure resistance (Ohm) or continuity. If you don’t have a multimeter, you can use the simplest test lamp with two wires, but this is less safe and convenient.
You will also need pliers for removing the terminals, a screwdriver for dismantling the casing, and possibly electrical tape for marking the wires. Do not forget to prepare a container with warm water if you plan to check the operation of the thermostat over time by immersing its sensitive tube.
- 📟 Multimeter - the main device for measuring circuit resistance.
- 🔌 Indicator lamp - an alternative way to check the presence of voltage (requires caution).
- 🧤 Safety gloves —to protect hands from sharp edges inside the refrigerator.
Make sure that the multimeter probes are in good working order. Connect them together: the device should show zero or emit a beep. This will confirm that the battery in the tester is not dead and the device is ready for use. A faulty tool may show a false lack of contact, which will lead to the mistaken purchase of a new part.
How to check a thermostat relay with a multimeter
The most reliable diagnostic method is to test the contacts. Locate the terminals on the thermostat housing. Usually there are two or three. If there are three terminals, then one of them is used for grounding or connecting an indicator light, and the other two are the main working ones. We need to find exactly the working pair.
Touch the multimeter probes to the two main terminals. If the thermostat is working properly and is at room temperature, the circuit should be closed and the device will show a resistance close to zero. If the device shows one (infinity), it means contacts are open. Try turning the control knob all the way clockwise. The contacts should close with a characteristic click.
☑️ Checklist for testing with a multimeter
For a deeper check, you can place the thermostat sensitive tube in the cold. Place it in a container of water and ice or simply put it in the freezer (if the design allows you to detach the case). After 2-3 minutes, when the temperature drops below the response threshold, the contacts should open, and the multimeter will show an open circuit. If this does not happen, the thermostat is faulty.
⚠️ Attention: Do not immerse the thermostat body itself with electrical contacts in water! Only the metal capillary tube needs to be cooled, otherwise you will cause a short circuit or damage the insulation.
Typical faults and their symptoms
Understanding the symptoms helps to quickly determine the diagnosis. If the refrigerator turns on and turns off immediately, buzzing for a few seconds, the problem may be in the compressor start relay, but often the thermostat is also to blame, which does not give a signal to continue operation. If the motor is completely silent, although there is voltage in the network, most likely thermostat contacts they do not close.
Another common symptom is that the refrigerator works non-stop. In this case, the contacts are “stuck” in the closed position or the bellows tube has lost its seal and does not respond to temperature changes. This leads to the formation of an ice coat and failure of the compressor due to overload.
| Symptom | Probable cause | Action |
|---|---|---|
| The compressor does not start | Open circuit in the thermostat | Replacing the thermostat |
| The refrigerator does not turn off | Sticking contacts | Replacing the thermostat |
| Frequent on/off | Incorrect calibration | Adjustment with a screw |
| Sparking inside the block | Burning of contacts | Urgent replacement |
Why sparks contacts?
Sparking occurs when the circuit blurs under load. If the sparks are too strong and a crackling sound is heard, it means that the contacts are burnt and their area has decreased, which increases resistance and heating. This is a harbinger of complete failure.
Sometimes the problem lies not in the part itself, but in incorrect installation. If the sensor tube is not deep enough into the evaporator or is misaligned, the temperature reading will be incorrect. As a result, the refrigerator will operate in the wrong mode, creating the illusion of a breakdown relay.
Replacing and setting up a new thermostat
If diagnostics confirm a malfunction, the part must be replaced. Thermostats cannot be repaired, they can only be replaced. When purchasing a new part, pay attention to the markings. The numbers and letters in the code (for example, TAM-133 or K-59) indicate the temperature range and length of the capillary tube.
Install the new thermostat into the housing, secure it and carefully lay the tube along the same path as the old one. It is important not to kink the tube or apply excessive force to it. After connecting the wires, turn on the refrigerator. Initial setup is usually not required, but adjustments to the position of the knob may be required.
Use a thermometer to accurately adjust the temperature inside the chamber. Place it on the middle shelf and wait a few hours. If the temperature does not correspond to the set value on the handle, fine tuning can be done through a special hole on the body or by turning the adjusting screw, if available.
Frequently asked questions (FAQ)
Is it possible to temporarily close the thermostat contacts to make the refrigerator work?
Yes, this is possible for a short-term check of the compressor or if you urgently need to store food until the technician arrives. However, you cannot leave the refrigerator with a shorted thermostat: it will work continuously, which will lead to freezing and damage to the motor.
Why does the new thermostat click, but the refrigerator does not turn on?
The click means that the contacts are closed, but the current does not reach the compressor. Check the compressor start relay and the integrity of the wires themselves. Perhaps the problem is not in the thermostat, but in the motor starting device.
How to understand that the length of the capillary tube is chosen incorrectly?
If the tube is too long, it will have to be rolled into a coil, which can disrupt heat transfer. If it is too short, the sensor will not reach the desired zone in the evaporator, and the refrigerator will not turn off or, conversely, will not turn on.
Is it necessary to defrost the refrigerator before replacing?
Full defrosting is not necessary if you have access to the thermostat. However, if you need to remove the back panel inside the chamber or defrost the ice around the tube, it is better to defrost the unit completely so that water does not get on the electrical contacts.