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Hermetic Compressor - Tecumseh

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17<br />

potential relay removes the start capacitor<br />

from the circuit after the motor<br />

is up to speed. This motor may<br />

use either:<br />

• an external thermal protector, or<br />

• an internal thermal protector.<br />

Permanent Split Capacitor<br />

(PSC)<br />

Here a run capacitor is in series with<br />

the start winding. Both run capacitor<br />

and start winding remain in the circuit<br />

during start and after motor is up to<br />

speed (see Figure 3-5). This normal<br />

starting torque motor is sufficient for<br />

capillary and other self-equalizing<br />

system. No start capacitor or relay<br />

is necessary. For additional starting<br />

torque, a proper start assist kit may<br />

be added (see Figure 3-6). Some<br />

start assist kits may include:<br />

• a wired-in Positive Temperature<br />

Coefficient (PTC) relay, or<br />

• a module Positive Temperature<br />

Coefficient (PTC) relay.<br />

This motor may use either:<br />

• an external thermal protector, or<br />

• an internal thermal protector.<br />

PSC motors are basically air conditioning<br />

compressor motors and are<br />

very common up through 5 HP.<br />

PSC Motor Starting<br />

<strong>Tecumseh</strong> Products Company pioneered the<br />

development of Permanent Split Capacitor<br />

compressor motors. This type of motor eliminates<br />

the need for potentially troublesome<br />

and costly extra electrical components, e.g.,<br />

start capacitors and potential motor starting<br />

relays (see Figure 3-5).<br />

To fully realize the capabilities of this simplified<br />

type of compressor motor, it is necessary<br />

to understand its starting and operating<br />

characteristics and the field conditions that<br />

can affect it.<br />

The following conditions affect PSC motor<br />

starting:<br />

• Low voltage: Reduces motor starting<br />

and running torque. A 10%<br />

voltage drop reduces a motor’s<br />

starting ability by 19%. Low voltage<br />

can cause no start, hard start,<br />

light flicker, and TV screen flip flop.<br />

Line 1<br />

Line 2<br />

Ground<br />

Control<br />

<strong>Compressor</strong> -<br />

Unit Ground<br />

FIGURE 3-4:<br />

FIGURE 3-5:<br />

FIGURE Line 1 3-6:<br />

Line 2<br />

Control<br />

Ground<br />

<strong>Compressor</strong> -<br />

Unit Ground<br />

Control<br />

Line 1<br />

Relay -<br />

Potential<br />

External or Internal<br />

Thermal Protector<br />

CSR motor diagram<br />

Start Winding<br />

Main Winding<br />

External or Internal<br />

Thermal Protector<br />

Line 1<br />

Control<br />

C<br />

Line 2<br />

S<br />

Ground<br />

<strong>Compressor</strong> -<br />

External R or Internal<br />

Unit Ground<br />

Thermal Protector<br />

Run Capacitor<br />

Control<br />

Line 1<br />

C<br />

Line 2<br />

PSC motor diagram<br />

S<br />

Ground<br />

<strong>Compressor</strong> -<br />

R<br />

Unit Ground Thermal Protector<br />

Line 1<br />

C Run Capacitor<br />

Plug-In<br />

C<br />

Run Capacitor<br />

C2<br />

S<br />

PTC<br />

Relay<br />

(115 Volt Only - Neutral)<br />

(115 Volt Only - Neutral)<br />

C1<br />

Line 2<br />

N<br />

Line 1<br />

C<br />

Ground Plug-In<br />

Run <strong>Compressor</strong> Capacitor -<br />

Unit Ground C2<br />

(115 Volt Only - Neutral)<br />

Line 2<br />

N<br />

Ground<br />

<strong>Compressor</strong> -<br />

Unit Ground<br />

(115 Volt Only - Neutral)<br />

Line 2<br />

C1<br />

Thermal Protector<br />

PTC Starting and<br />

Protector Package<br />

PSC motor diagram<br />

C<br />

with start<br />

assist Relay kit -that includes a module<br />

PTC Potential relay<br />

C<br />

S<br />

R<br />

PTC Starting and<br />

Protector Package<br />

External or Internal<br />

Thermal Protector<br />

Relay -<br />

Potential<br />

PTC<br />

Relay<br />

Start Winding<br />

External or Internal<br />

Thermal Protector S<br />

RC<br />

R<br />

C<br />

S<br />

R<br />

inding<br />

Start Winding<br />

Start Winding<br />

Main Winding<br />

Main Winding<br />

Start Winding<br />

Main Winding<br />

Start Winding<br />

Main Winding<br />

Main Winding<br />

ding

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