They’re essential for compressors to work well

Electric components have a vital role in the compressor’s operation. For this reason, the diagnosis made by the contractor in any refrigeration system should include a careful check of the state and the correct application of the relay, start capacitor and thermal protector, as well as, in some cases, the inverter.

To begin with, it’s important to remember that not all compressors use a starting capacitor and running capacitor, and that there are different types of relays, PTC, in addition to the TSD devices (Time Starting Device), used in high-efficiency models. Also the thermal protectors may vary between the 3/4 and 4TM.

Another essential piece of information is that compressors of the same family with similar capacities may not always use the same electric components. The electrical kit is determined based on the compressor’s voltage, frequency and operating envelope (L/M/HBP). Furthermore, even in the same family, there are models which work with low starting torque (LST) or high starting torque (HST), which causes differences such as, for example, the mandatory use of a starting capacitor or the existence of bridges for relays, connecting the terminals.

So when a replacement is necessary, always refer to the compressors’ datasheet in the electronic catalog available on Embraco’s site. For this search, the key information is model, voltage and frequency, which are available on the compressor’s label.

When there is a need for a substitution, improvising or resorting to a solution that isn’t recommended is not advisable. This action can cause serious problems, including compressor burn out. Special attention should also be given when assembling components. In general the sequence is as follows:

  • Mount the starting device and thermal protector;
  • Make the electrical connection of the capacitor to be used;
  • Mount the support holder and capacitor.

But it’s necessary to check the specific characteristics of each compressor model and, based on this know the details of these three steps.

Common mistakes in choosing electric components:

1. Assuming that compressor models with the same motor power use the same electric components.

Example: when placing a relay/protector set of an EMI30ER compressor for use in blends and low (LBP) applications, in an EMIS30HHR model for R134a and for use in low/medium/high (L/M/HBP) application, the electric kit will not work properly. In other words, the thermal protector may not trip or the starter motor will not turn off at the appropriate time, causing the compressor to burn out.

2. Using a lower voltage capacitor than that specified.

Example: replacing an 88-108 μF/150V capacitor, sometimes the contractor opts for a 120 V model. The correct decision would be to use a capacitor with a voltage equal to or greater than that indicated so as to withstand voltage spikes of the normal on-off cycle and thus avoiding the risks of damaging the compressor.

3. Not taking into account the refrigerant type used in the compressor.

Example: electric components for 1/5 HP compressors using blends and R134a are different. Using the wrong relay/thermal protector set can cause premature shutdown or failure to shutdown in situations where it would be necessary.

To learn more, see Embraco’s electronic catalog.

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Thermal protector: serves to protect the motor from faults at startup and overheating in normal operating conditions.

Relay: controls the on/off operation of the starting coil (auxiliary coil) by turning it on to assist in starting the motor and turning it off just before the motor reaches its rated speed or normal speed.

Start capacitor: Increases the compressor’s starting torque, assisting it at start times. Its use is mandatory for motors with high starting torque (HST).

Running capacitor: allows current flow through the compressor’s auxiliary coil after it starts, allowing the auxiliary coil to also contribute to the motor’s operation.

Inverter: automatically adjusts the compressor’s speed according to the variation of the system’s thermal load. It’s only used in variable speed compressor models, such as Embraco Fullmotion.


Errata: In edition 116 of the printed magazine, in the Running Capacitor Application table, where it reads “PTC with running capacitor in EM compressor”, it should read “Relay with starting capacitor in F/EG compressor”.

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