Application Note

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The core of a refrigeration sys-

tem is the compressor, which is

designed to pump cool refriger-

ant gas from the evaporator into

the condenser. To accomplish

this task the compressor raises

the temperature and pressure of

the low superheated gas, forcing

it into the condenser. The com-

pressor should never pump liq-

uid. This will not only damage

the compressor, but can create a

potential safety hazard.

Similar to the human heart,

the refrigeration compressor

needs to be properly maintained

and requires periodic inspection

and testing. Unfortunately, the

compressor is often ignored until

it malfunctions or stops running

altogether, at which time it gets

replaced and the system is back

up and running – temporarily.

Often times the culprit is not the

compressor, but a system failure

or desig

n problem w

ith acces-

sory equipment which killed the

compressor prematurely.

This application note describ

how to troubleshoot a compres-

sor and the associated problems

that can cause a system to fail

prematurely. We will discuss the

proper methods of diagnosing

and repairing system problems,

rather than just their symptoms.

Measuring the compressor

suction and discharge

pressure

Both the suction and discharge

pressures at the c

ompressor are

normally measured with a stan-

dard set of refrigeration gauges

However, this application note

will explain how to measure

both pressures on the suction

and high side of the system with

your digital multimeter (DMM)

and a pressure/vacuum module,

with or without your standard

gauges. If the gauges are left on

the system and used in conjunc-

tion with this test, the module

will verify the accuracy of the

standard manifold gauges.

To measure the pressures on

your DMM in conjunction with

your standard manifold gauges,

take the following steps:

•

Attach the pressure/vacuum

module hose fitting to the

refrigerant service hose on

your manifold gauge set, usu-

ally the yellow hose.

•

Attach the pressure/vacuum

module to a DMM and set the

module function to cm/in Hg.

•

Install your blue and red

hoses to the suction side and

high side of the system as

during any normal service

process.

To read the suction pressure on

your DMM, open the blue handle

on the manifold gauges. This

puts the system suction pressure

into the pressure/vacuum mod

ule. Read the pressure on the

digital readout and compare it to

the gauge pressures

. D

on’t be

alarmed if the pressures don’t

match exactly. Modules like the

Fluke PV350 are typically much

more accurate than a standard

set of refrigeration gauges.

To read the discharge pressure

on your DMM, close the blue

valve on your gauges and open

the red handle on the manifold

gauges. This puts the system

discharge pressure into the

module.

To remove the module, simply

reverse the process you followed

when installing the unit.

Caution: Be sure to close the

high s

ide p

ort of your gauge

first, and remember to remove

the refrigerant from the high

ide gauge by allowing the com

ssor to run and pull exce

refrigerant into the low side of

the system.

Troubleshooting the

HVAC/R refrigeration

cycle for mechanical

problems

Application Note

From the Fluke Digital Library @ www.fluke.com/library

Summary of content (4 pages)

PAGE 1
Troubleshooting the HVAC/R refrigeration cycle for mechanical problems The core of a refrigeration system is the compressor, which is designed to pump cool refrigerant gas from the evaporator into the condenser. To accomplish this task the compressor raises the temperature and pressure of the low superheated gas, forcing it into the condenser. The compressor should never pump liquid. This will not only damage the compressor, but can create a potential safety hazard.
PAGE 2
To measure the pressures on your DMM and pressure/vacuum module without installing your manifold gauges, take the following steps: • Attach the module hose fitting to any standard refrigerant service hose. • Connect the refrigeration hose to the service port on the compressor. • Open up the service port and read the refrigerant pressure directly on the pressure/vacuum module.
PAGE 3
Compressor valve performance test To test small hermetic and semi-hermetic compressors used for medium and low temperature applications, the following method can be used to test for internal valve leakage. (see figure 2) 3 Fluke Corporation OFF kPa psi ZERO METRIC ENGLISH PRESSURE / VACUUM MODULE cmHg in Hg Compressor PV350 you to detect problems that may go unnoticed with a single system check.
PAGE 4
Troubleshooting compressor electrical motor failures caused by refrigeration system problems Occasionally defective compressors with electrical winding failures are diagnosed by a service technician as caused by an electrical system problem. However, mechanical system failure or inferior installation and service practices often cause compressor electrical problems. These problems include: 1. Poor piping practices resulting in oil not adequately returning to the compressor during the run cycle. 2.