How to test fridge compressor with multimeter

If you are wondering how to check a refrigerator compressor, you have come to the right place. Let us guide you to check your compressor correctly.

Table of Contents Show

How to Check a Refrigerator Compressor
Other Things to Check
How to Check a Refrigerator Compressor Relay
How to Check Refrigerator Compressor Gas
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Checking Compressor Windings Using Multi Meter

How to Check a Refrigerator Compressor

It is essential to disconnect a refrigerator from electric power before performing any repairs. To begin, pull the refrigerator from the surrounding wall and disconnect it. If it is impossible to reach the power cord, turn off the circuit breaker.

Next, create enough space at the bottom back of the refrigerator for you to fit and work. Get a digital multimeter and set it to Ohms. Locate the start relay on its mount in the compressor. The relay is typically small, but you cannot miss it.

Once you unmount the start relay, you will see the start, run, and common pins. Some compressors will mark them with alphabets S, R, and C while others won’t. So, if your refrigerator compressor has no markings, set the meter to R x 1 scale. Then, locate the two electrical pins out of the three with the highest resistance reading.

Now, use the meter’s probes to test between two pins. The two pins with the highest resistance are the start and run pins. The third one automatically becomes the common terminal. Now, if you find an O.L reading between any two of the electrical points, the compressor has an open circuit and you should replace the compressor.

Other Things to Check

Another way to check a refrigerator compressor is to check the motor windings. Get a reading between the common and start and the common and run electrical pins using a multimeter. The readings should stay within 0.5 ohms, one to the other.

However, the motor winding that shows the lower reading is shorted if the readings are not within the recommended ranges but veer off significantly. It indicates the compressor is faulty and needs a replacement.

You can also check the reading between the housing of the compressor and each electrical pin. That is, if the motor winding test is inconclusive. The multimeter should read O.L while you take the readings. So, if you get any other readings, replace the compressor because the motor windings are shorted.

Thermostatic Control

If the windings of the compressor’s motor test well, check the thermostatic control. The control is a switch so set it between four and five. Test the continuity between the relay wires and the plug. You should get a reading of 0.000 when you test one start relay wire and one side of the plug. If the meter shows O.L, the control is malfunctioning and needs a replacement.

But if the control shows the correct reading, the compressor fault may stem from the start relay itself. It could also be that the compressor is locked up or has worn valves or bearings. Replacing the start relay is quick, easy, and inexpensive. Replacing the compressor, on the other hand, is the job of a licensed refrigerator technician, according to the law in the U.S.

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Refrigerator Compressor Relay [How to/Issues & Solutions]
Refrigerator Gas [Questions, Problems & Solutions]

How to Check a Refrigerator Compressor Relay

To check the start relay of a refrigerator compressor, do the following:

Unplug the refrigerator from the wall outlet. As with the compressor, don’t test or repair any part of the appliance while it is still connected to electricity. Next, find the relay on the side of the compressor and unmount it.

Give it a shake to determine whether or not it rattles. If the relay rattles, it is a sure sign that it is faulty and needs a replacement. The same is true if it smells burnt. But if the relay does not rattle, check it for continuity.

There are usually three terminals on a relay. Each one is marked with letters, so you may find S, L, and M on the terminals. Take a multimeter and place its probes on any two of the terminals. Turn the relay bottoms up while the probes are still attached to the terminals. You should hear an audible click and the meter should read infinity.

Do the same all across the terminals. Test terminals S and M, S and L, and M and L. If the reading on the meter changes, replace the start relay.

How to Check Refrigerator Compressor Gas

To check the gas or refrigerant in the refrigerator, do the following:

Step 1

Place a hand close to the condenser coils. You should feel some warmth coming from them. But if the coils have no warmth or feel cold, it may mean there is little or no gas running through the refrigerator.

Step 2

Disconnect the refrigerator from power and put one ear to the refrigerator’s side. You should hear the gas gurgling and hissing. If you don’t hear these noises, the gas may be low. But it could also be a fault with the condenser coils, condenser fan, defrost system, compressor, or cap tube.

Step 3

Remove the interior rear panel of the freezer to see the evaporator coils. Now, reconnect the refrigerator to electric power and allow it to operate for several minutes with the panel still uncovered but with the refrigerator door shut. If the coils have no frost on them after the refrigerator has run for several minutes, the gas is low or absent.

Recap

Hire a refrigerator technician to check the compressor if you suspect it is no longer working as it should. But if you are a DIYer and want to know how to check a refrigerator compressor yourself, this article will guide you.

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In this post, you will learn about checking compressor windings or testing compressor windings. As you that in the refrigerator or fridge compressor we have an electric induction motor that rotates the pump. In fridge compressor mostly in rated in single phase which has 3 terminals. I already publish a post about the start, run, and common identification guide on this blog.

Sometimes when our refrigerator compressor stop working or not running a problem then we must call a professional to test the compressor or refrigerator. But if you want to check your compressor himself then this post is for you.

In this post, I am telling you about some main and common reasons for compressor not working and about testing compressor methods. There are many problems which we face in the electrical refrigeration system and due to which or refrigerator or Air conditioner stop working. But this post especially about the check compressor motor winding.

Checking Compressor Windings Using Multi Meter

As you know that in single-phase fridge or air conditioner compressor we have internally instilled a single phase motor that consists of two types of winding which we called main winding (ruining winding) and Auxiliary winding (starting winding). But if the compressor has receiving the power supply and still not working or running then maybe its starting capacitor or relay is not working. But if you want to test compressor winding then follow the below steps.

First of all, I want to give an example of a fridge compressor

If you want to check your fridge compressor then flow the below steps.

First of all plug out the fridge main electric plug. or switch of the supply which is connected to the fridge.
Then see the relay and find out which one terminal is common, start and run. The common terminal will be connected to the overload protector or connect directly to the electric supply wire. (note that direct wire was connected in those single phase compressor, in which the overload protector is instilled internally).

After that find out the run terminal, in PTC relay the 2nd supply wire will connect directly to the run terminals of the compressor, which means that the 2nd wire connects to the relay point and that point supply goes to direct a terminal of the compressor will be your run terminal.

Now you find out the common and run terminal of the fridge compressor. So the other wire will be the start terminal, otherwise, 2nd supply wire will be connected to the start terminal through a capacitor or heating resistor. (note that heating resistor is instilled internally in PTC relay).

Now you find and mark your compressor terminal. Now set your multimeter knob on connectivity text or Ohm. Now connect one lead of the meter to compressor common and other connect compressor uninsulated body place. Continue this process with the start and run terminal.

Now if you find our connectivity of winding and body then it means that your compressor winding is short with compressor body or winding is uninsulated with iron core. And if have not connectivity between terminals and body. Then flow the next step.

The next step to test its resistance between one another. Test the compressor by unsung the below method. So first read the below post, and flow the method to test the compressor.

How to identify compressor terminals?

Now if your compressor terminals reading shown the same as in the above post then your compressor winding is not burned or if it’s shown different reading between common, start and run then your compressor winding is burned.

Now if compressor winding resistance shown the same as I have shown in the identifying compressor example then change your PTC (positive temperature coefficient thermistor) relay and com.. overload protector or capacitor and if still not working then call a professional.

Mostly in some compressor in which the common terminal is on the upper side then the left side will be start and the right-hand side will run terminal, and Danfoss compressors in which the common terminal on the downside the right side will be start terminal and left side will be run as I have shown in the below diagram.

How To Test or Check Air Conditioner Compressor Motor Windings

Now if you want to check the Air conditioner compressor then it’s also too simple, in the air conditioner compressor we have labels in which the R, S, and C written or parked.

However, if this rubber label is not available or removed then follow the below steps.

First of all, the terminal of the air conditioner compressor terminal is connect to an overload protector or direct to supply wire is your common terminal. Mostly we use white or black color for common. The other supply wire will be connected to a capacitor and to compressor terminal will be your run terminal, mostly in split unit AC the blue color wire is used for the run terminal. And the other wire will be your start terminal which will be connected to the capacitor. Mostly this red color wire used to start a terminal connection.

Now set the multimeter on ohm or resistance tasting or use an ohmmeter and check the compressor, follow the same method as we use for the fridge compressor terminal. However, let’s see the example.

If your resistance between common and ruining is lower than resistance between common and starting then all is right and your compressor is winding is good condition and if that shows different results then compressor winding is burn or cross.

If it’s shown good results then flow the steps.

Now test the compressor shortage between Compr…. terminals with compressor body like fridge compressor and if the meter showed no reading then compressor winding is no shortage with the body and if it’s shown the reading then it means that compressor windings are shortage with compressor body.

Now if you check compressor motor windings and not find any problem and still compressor did not run then change the capacitor and if still compressor not working then check the overload protector.

As you know the overload protector is connected to the main terminal of the compressor in series and if the compressor overload protector stops working or internally open, the compressor also stops working. However, these are simple methods for checking compressor windings of single-phase and now if you have any questions then you can use the below comments section.