# What is Role of PTC Relay and How a Compressor PTC Relay works

In my last post, I talk about compressor overload, and in this post, you will learn about PTC Relay which we use mostly for every refrigerator compressor starting. PTC means a positive temperature coefficient thermistor however we can call starting relay or compressor starting relay in simple words.

## How a Refrigerator PTC Relay Working and Function

In the refrigerator compressor, we use the split-phase single phase induction motor and this motor has two internal types of winding which we called running and starting winding or auxiliary winding. We know that a single phase motor did not start without a starting capacitor or a starting current.
In simple words, the refrigerator PTC relay gave a current to start winding and when the motor starts up the PTC compressor relay removes the start winding from the circuit.
So the above is a simple and short explanation of refrigerator relay and its working, So let’s know the working method of a PTC.

As I wrote above that PTC means a positive temperature coefficient thermistor which means that a relay with working relation with temperature. Basically, a PTC thermistor is a resistor whose resistance increase with the increase of temperature.

So let’s explain it step by step
We know that the compressor motor or fridge compressor has a split phase induction motor which has two types of winding, the main winding which we called RUN Winding, and the auxiliary winding which we called START Winding. A fridge compressor requires a starting current to start normally and for this, we connect the starting relay.
Compressor three terminals called START, RUN, and COMMON. Common means the point where the start and run are connected.

How to identify refrigerator compressor terminals

We connect the overload protector to the compressor common terminal and the PTC relay to the run and start terminal. In the PTC relay the supply goes direct to the run winding but between the supply and start winding a thermistor is connected in series and when we switch on the refrigerator the current start flowing through the thermistor to the auxiliary and compressor start-up, this current flows heat thermistor and due to temperature, the resistance of thermistor high and thermistor remove the start winding from the supply.
E.g Example: If you start your fridge and then you switch off and then start it, you will note that the compressor does not start again because of the heat thermistor or relay. And when you switch it off again and try after 5 to 10 minutes you will find the fridge compressor starts normally.

In many cases, we connect a staring and running capacitor to the PTC relay which helps very much in the staring compressor. With the starting capacitor, we connect the PTC relay thermistor in series which makes removes of start capacitor from the circuit. In many PTC compressor relays have a connection point for the run capacitor and we connect the run capacitor in parallel with a relay which helps in better starting and running the compressor.

#### Message :

I hope you learn something from this post about the PTC compressor starting relay and its working, however, I will guide you about all types of PTC relays and their wiring methods with complete diagrams.

### 17 thoughts on “What is Role of PTC Relay and How a Compressor PTC Relay works”

• September 6, 2016 at 2:50 pm

I have a frigidaire chest freezer that sat in a few inches of water for a day. it continued to work for a week, then stopped. I've tested the compressor and the temperature control. I believe the problem is the ptc relay. The manufacture says the part is not replaceable. Can I substitute a different start device, along with a run capacitor to accomplish what's needed?

• September 9, 2016 at 5:42 am

Dear can you send me the images of the compressor and relay, and one thing more test the compressor terminals and find out the star run and common. and when you find out then connect a relay regarding the terminals, my mean that replace a relay which M point match with your compressor run terminal and S point match starting terminal.
In some compressor the overload protector is instill internally and in some the overload is connect with PTC rely. if your old relay have an overload protector then connect a overload between the common terminal and supply wire. and if overload is not instill with old relay then connect the other wire to the common terminal.
Before you starting doing this , switch off the supply wire and May ALLAH Safe you and best of luck.
However if you send some images then i will try my best to help you. And you can also connect a starting or running capacitor with relay but if the relay have points for capacitor or the relay is capacitor type relay. The below post will help you.

http://www.electricalonline4u.com/2015/07/compressor-terminals-identifying.html

• September 9, 2016 at 6:04 am

I am using two compressors.I want to connect a capacitor to one refrigerator compressor? I'm trying to make two compressors run on Infinity Loop please make a diagram I appreciate it very much thanks!

• September 9, 2016 at 6:05 am

I am using two compressors.I want to connect a capacitor to one refrigerator compressor? I'm trying to make two compressors run on Infinity Loop please make a diagram I appreciate it very much thanks!

• September 10, 2016 at 5:13 pm

• November 5, 2016 at 4:17 pm

i have a frigidare chest freezer that wont run just clicks after its on for 1 min or so ordered new start relay and overload need a diagram of where the wires should be think someone else has messed with them

• November 5, 2016 at 4:18 pm

i have a frigidare chest freezer that wont run just clicks after its on for 1 min or so ordered new start relay and overload need a diagram of where the wires should be think someone else has messed with them

• November 5, 2016 at 4:32 pm

Dear if yo want to instill the a new relay frigidare chest freezer compressor then first identify the compressor terminals that which one is star,run and common then when you find out that. Connect your overload protector to common terminal. And relay point which for (M) point running connect to run terminal.
This will be best for you to seen us some images of your compressor and relay and overload using my email id. One thing more That IN SHA ALLAH Soon i will write about this……..

• October 18, 2019 at 12:04 pm

It’s an amazing blog your writing skills are very good. Also, within your appreciation, I just want to add that if you are also facing some problem with your refrigerator and want to repair it ASAP then contact Airwin Aircon & Fridge Services where you will get professionals for your Fridge Repair Singapore.

• May 26, 2020 at 3:44 pm

Explained it in a very nice way.well done

• August 22, 2020 at 11:50 am

whoah this blog is fantastic i love reading your articles. Keep up the great work! You know, lots of people are looking around for this info, you could help them greatly. I appreciate, cause I found just what I was looking for. You’ve ended my four day long hunt! God Bless you man. Have a great day. Bye what is ptc heating element

• January 26, 2021 at 11:36 am

It was absolutely a handy work for the readers and home appliance fans. The role of PTC, compressors works and the functions of refrigerators PTC relay you described with technical presentation were super helpful and worth to be praised. Though I was intended to find online support for freezer repair company, I was drastically impressed with the details. Surely you deserve huge cordial thanks.