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Automobile Engineering

Sight Glass

Introduction:

A sight glass or water gauge is a transparent tube through which the operator of a tank or boiler can observe the level of liquid contained within. The sight glass is fitted into the top of the receiver-drier or built into the manifold gauge assembly.

Purpose of the sight glass:

  • To obtain the maximum efficiency from the air-conditioning system, it is very important that it is charged with the correct amount of refrigerant.
  • The sight glass can be used, by the experienced technician, to check the amount of refrigerant in the system.
  • The main purpose of the sight glass is to visually check the condition of the refrigerant passing through the system.
  • There are several ‘indicators’ that help the service technician to diagnose possible problems.
  • The sight glass should only be used to gain a quick response to a problem and should be supported using a charging/reclaiming station.

 

Because R134a refrigerant shows a milky colour when viewed with a sight glass it is not used a great deal for system diagnosis. R12 systems generally use the sight glass for additional diagnostic information.

 

Sight glass clear

 

A clear sight glass indicates the system has a correct charge of refrigerant. It may also indicate that the system has a complete lack of refrigerant (this will also be accompanied by a lack of any cooling action by the evaporator).

 

Note – the sight glass may be clear but the system might be overcharged (too much refrigerant).

This must be verified by connecting the charging trolley and checking the gauge readings.

Sight glass foamy

 

A ‘foamy’ or ‘bubbly-looking’ sight glass indicates the system is low on refrigerant, and air has probably entered the system.

However, if only occasional bubbles are noticed during clutch cycling or system start-up, this may be a normal condition.

 

Sight glass streaky

 

If oil or streaks appear on the sight glass a lack of refrigerant may be indicated.

 

Sight glass cloudy

 

A cloudy sight glass indicates that the desiccant contained in the receiver-drier has broken down and is being circulated through the system.