function of timer in frost free refrigerator

There are many separate components in a refrigerator's defrost system that must work in concert for a frost free system to work properly. We will attempt to explain the workings using simplified electrical schematics.
The heart of the defrost system is the defrost control. The most common control is a mechanical defrost timer which is a motorized device that opens and closes several electrical contacts. Each contact can be thought of as a simple light switch but instead of a light, one connects the defrost heater circuit, another connects the cooling system. When one of these is switched on, the other is switched off. A motor on the timer (NOT illustrated) turns a cam that opens and closes these contacts at set intervals (see below for other types).
Cooling Cycle

During the cooling mode, the defrost timer closes a contact to the compressor circuit so it will run. The circuit to the defrost heater is open.
While in this mode, the thermostat (a.k.a. cold control) cycles the compressor and fan motors on and off to maintain an appropriate temperature.

How To Test the Defrost Timer

A mechanical defrost timer controls the defrost cycle of the freezer. In older models, the timer runs continuously and roughly every six hours, cuts power to the cooling system and sends power to the defrost heater. In newer models the timer advances only while the compressor or defrost cycle is running - an improvement for efficiency. As the timer continues to advance, power to the heating element is cut and power is restored to the cooling system. If the timer does not advance, the appliance will be stuck either in defrost or refrigerate mode, resulting in, respectively, no cooling or frost build-up.
Caution: Please read our safety information before attempting any testing or repairs.
 Before testing the defrost timer, unplug the refrigerator to avoid an electrical shock hazard.
The defrost timer is usually found behind the front grill "toe kick" of the refrigerator. It may also be found behind a cover plate inside the refrigerator or freezer, in the temperature control console, or behind the refrigerator near the compressor.
To test whether the defrost timer is simply failing to advance, locate the advance screw and turn it clockwise until you hear it click. This advances it to the next mode. If it was cooling before, it is now in defrost mode. Simply wait about 35 minutes and check whether it has left defrost mode and has resumed cooling (listen for the compressor). If it does not advance, the timer motor is probably bad and the entire timer needs to be replaced. If it advances as it should, then you can follow the steps below to test the switch electrically.
The timer is usually held in place with one or more screws. Remove the screws and gently pull the timer out far enough to disconnect the wiring connector. The connector can be removed by firmly pulling and rocking it left and right. It is not necessary to note the position of the wires because the connector plug is keyed so that it can be replaced in only one way.

Relays Motor Compressor

A hermetic compressor motor relay is an automatic switching device designed to disconnect the motor start winding after the motor has come up to running speed. The two types of motor relays used in refrigeration and air-conditioning compressors are the current and the potential type.

The current-type relay

 is most often used with small refrigeration compressors up to 1 hp. Where power is applied to the compressor motor, the relay solenoid coil attracts the relay armature upward. This causes bridging contact and stationary contact to engage (see Fig. 7-30). This energizes the motor start winding. When the compressor motor comes up to running speed, the motor’s main winding current is such that the relay solenoid coil de-energizes. This allows the relay contacts to drop open, which disconnects the motor start winding.

One thing to remember about this type of relay is its mounting. It should be mounted in a true vertical position so that the armature and bridging contact will drop free when the relay solenoid is de-energized.

What is AHU and FCU

FCU VS. AHU

In simple terms, an air handling unit (AHU) is a component of an HVAC system that cools and distributes air into the space through a duct.

A fan coil unit (FCU) is a standalone system that circulates the existing air in a small space, but it can also be a part of an HVAC system.

You will find a comprehensive overview of AHUs in one of our earlier posts, but to summarize: an AHU is a system that conditions and circulates air through the building’s duct. It comprises of multiple components, such as a blower, sound attenuators, and cooling and heating coils.

Each AHU component is a system in itself. In fact, you have multiple design and configuration options for each one, enabling you to build an AHU centered on your building’s specific needs.

The upfront selection and installation process involved with AHUs is extensive — and expensive.

You must configure your AHU system correctly to ensure that your HVAC system runs efficiently. An inefficient HVAC system consumes excess energy and raises your building operating costs.

In addition, an inefficient HVAC system can also fall into disrepair, which will cause maintenance issues and escalate your building lifecycle costs.

Air Handling Unit (AHU)

Fan Coil Unit (FCU)

An FCU is not as complex or extensive as an AHU. It’s a singular system that can operate on its own to circulate air in an area without ductwork.

One major difference between FCUs and AHUs is that AHUs can bring in outside air and heat or cool it (i.e., conditioning). However, FCUs can only condition the air that’s already present in the area by pulling it in and moving back out through its heating or cooling coil.

As a result, FCUs are typically used to heat or cool small areas, such as a private gaming room in a casino. The typical FCU will cover a space of 150m2.

AHUs are more common in large buildings with a centralized HVAC system, such as Underfloor Air Distribution (UFAD). AHU-based HVAC systems are also less noisy than FCUs.

On the other hand, FCUs are also much cheaper to procure and install than AHUs. You can also get FCUs in a variety of configurations, including floor-mounted and ceiling.

The cost and variety of configuration options make FCUs attractive for houses and apartments without HVAC. However, FCUs might also be sought to support an AHU-based HVAC system by covering areas that are not connected to the HVAC’s ductwork.

ការងារបូមសំអាត ម៉ាស៊ីន ពេលដំលើងម៉ាស៊ីនត្រជាក់ថ្មី

ក្នុងការចាប់បូមសំអាតនេះត្រូវមាន៖

•  នាឡិការហ្គាស  ​​​Gauge Manifold
• ម៉ូទរ័បូមសំអាត     Vacuum pump

លំដាប់កាងារៈ

·        ចាប់នាឡិការហ្គាសនេះទៅនឹងម៉ាស៊ីនត្រជាក់  ទុយោធំ សំពាធទាប  ដោយប្រើ ទុយោហ្គាស ពណ៏ ខៀវ

·        ចាប់ទុយោហ្គាសពណ៏លឿងទៅ នឹងម៉ាស៊ីនបូមសំអាត

·        ធ្វើការបូមសំអាត ឲម៉ាស៊ីនបូមសំអាតដំណើរការ

·         ត្រូវទុកអោយម៉ាស៊ីនបូម   បូមសំអាតរហូតដល់ ក្រោម -30 PSI នៅលើនាឡិការហ្គាស

*ចំណាំ  ក្នុងពេលបូមសំអាតនេះ  ម៉ាស៊ីនមិនដំណើរការទេ

How to clean your air conditioner