The Testo 550 was engineered to be a perfect balance of features,
benefits and value. Features of the 550 include high accuracy pressure
transducers, low mass temperature sensors, 3-way manifold configuration
and magnifying sight glass. These allow a service technician to easily
evaluate both sides of the refrigeration system while displaying
pressures, saturation temperatures, superheat and subcooling. All of
this is packed into a rugged, compact and affordable package that will
fit any technicians budget.
Lower initial cost and low cost of ownership
Keeping high quality standards in the forefront, Testo engineers had a
daunting task to make the 550 more cost competitive without compromising
the quality of the measurement. The outcome was a product that has
fewer parts for quicker assembly, a redesign of the temperature sensors
to make them more robust (while less expensive) and a more compact
The 550 has a separate button for almost everything nine of them to be
exact. More keys means eliminating the need to always scroll through
multiple menus and sub menus to get to configuration settings. There is a
power key for power, and back light key for the display, a setup key
for easy configuration, mode keys for different modes, a refrigerant key
to select over 31 on board refrigerant profiles, min/max/mean key for
quick system analysis, zero key for the pressure transducers and arrow
keys to make selections.
The 550 has a brighter and better defined display than previous models.
Decimal points and other display characters have been enlarged for easy
viewing from a distance.
Integrated hose holder and hook
The 550 has 3 brass integrated hose parks that are positional by the
user to the back or front of the instrument. Residential technicians
that typically set their gauges on the ground can now do so without fear
of dirt, moisture or other potential system contaminates picked up by
the hose parks entering the refrigeration hoses when they are in the
stored position. A relief machined into the end of the hose park allows
room for the Schrader depressor and a positive seal that will keep
moisture from entering the hoses in the parked position. The hook is
integrated into the 550 and designed so it can easily be stored if kept
in an instrument case or tool bag.
User configurable units of measure
This can be very helpful if you come across foreign equipment that may
not have specifications in English units of measure. The 550 can easily
be configured to measure pressure and temperature in System
International (SI) or the English customary system, eliminating time and
error in converting to the desired units of measure.
Vacuum displayed in inches of mercury
Automatic change of units when the 550 goes into a vacuum allows the
technician to easily determine when proper recovery levels are met or to
set pressure switches in systems that operate below atmospheric
pressure in refrigeration applications. While the 550 is rated for use
in vacuum, Testo recommends the use of an auxiliary micron gauge during
evacuation. The 550 does read and indicate vacuum, but does not have the
resolution to display vacuum in microns. If you are looking for an
intregrated Vacuum gauge look at the Testo 557.
Simultaneous measurement of superheat and subcooling
With dual temperature sensor porting standard, the 550 can be used with a
second optional probe for charging and troubleshooting without the need
to move the temperature sensor. Watching both sides of the system while
charging allows the technician to spot problems like a faulty expansion
valve at system start-up before the system is overcharged. When
performing any diagnostic testing, both sides of the system must be
evaluated before adjustments to the charge or mechanical repairs are
The Testo 550 utilizes dual ceramic thick film pressure transducers or
pressure-measuring sensors, with a pressure range of -14.7 to 580 PSIG.
Ceramic pressure-measuring cells have a measuring accuracy and
repeatability that is stable over a very long time; therefore frequent
calibration is not needed. The high and low side sensors are matched and
selected for an operating range that will provide the highest accuracy
for their desired measuring range, allowing accurate pressure
measurement over the full range on either side. The pressure transducers
are calibrated in regards to their zero points, coefficient of thermal
expansion, and sensitivity so they can be used in wide ranges of
temperatures as extra-high precision pressure transducers. Ceramic
pressure transducers are designed so the pressure sensitive part is
exposed directly to the refrigerant. Thanks to excellent chemical
resistance, ceramic pressure transducers do not require additional
protection from oils, refrigerants, or acids and additionally will
withstand the shocks from normal to rough handling without ever
affecting the sensor calibration. While traditional gauges require
frequent trips to a calibration house to assure their accuracy (often a
procedure never performed), the calibration of the pressure transducers
in the Testo 550 is only recommended annually.
Altitude compensation adjustment
Like all manufacturers of digital refrigeration gauges, Testo uses a
relative pressure transducer that is zeroed to atmospheric pressure.
While relative pressure transducers are a very cost effective solution,
they, like Bourdon tube gauges, require adjustment when used above sea
level. Because the work site atmospheric pressure is typically not the
same as pressure at sea level for standard air conditions compensation
for barometric pressure needs to be considered for critical charging
applications. In the configuration menu, the technician can now input
actual barometric pressure in inches of mercury and compensate for
pressure measured above sea level or that caused by changing weather
conditions. This allows for a technician in an area of the country like
California to work as accurately at 7000 ft as at sea level without the
need for altitude corrected pressure temperature charts.
Standing pressure test with temperature compensation
During initial commissioning or after repair, a standing pressure test
is required to verify system tightness over a prescribed time period.
The 550 incorporates a timed and temperature compensated pressure drop
test that allows the user to see the initial pressure, final pressure
and the difference over time. No more marking you gauge position,
tapping the gauge and measuring the time with a stop watch.
When charging a system, hunting is a common problem during low loads.
With the min/max/mean function in the Testo 550, the technician can
easily determine what the average superheat is and verify that the
system is not intermittently flooding. Pressure switch cutouts both high
and low can be verified quickly and easily.
The Testo 550 uses NTC thermistors for temperature measurement with a
range of -58 to 302F. The NTC thermistor has several advantages over K
type thermocouples including temperature sensitivity, electrical noise
immunity, and a lower replacement cost (about 1/4 of the cost). The
clamp probe has also gone through an extensive redesign to be easier to
use, more robust, and lower cost. With a 1-3/8" capacity, the standard
clamp probe will easily fit around all lines on residential heat pumps
and air conditioning equipment. Utilizing low mass electrically shielded
thermistors, the 550 clamp probes have excellent response time and
temperature measurement characteristics.
Delta Temperature Calculation
Using the Delta Temperature mode and a second temperature probe, system
components like reversing valves and refrigerant liquid line dryers can
easily be evaluated for excessive temperature drops and or leakage which
will result in capacity losses and other associated problems. System
approach can quickly be determined, by measuring liquid line
temperatures and outdoor air to properly charge a system, and
temperature across refrigeration coils can be verified to fall within
Replaceable valve assembly
Easy to service with basic hand tools, the piston and valve packing
assembly are field replaceable. The valve handle can easily be removed
by pulling the retaining spring clip with a small screw driver to gain
access to the valve assembly.
Every unit is leak tested with helium to ensure tightness. By performing
this procedure we can insure that the 550 will work in both pressure
and vacuum without leaks.
Oil, moisture and impact resistance
The Testo 550 is designed to withstand rigors of day to day service and
replace the gauges that you now carry. Designed to withstand exposure to
POE and mineral oils as well as refrigerant the case will not easily
discolor or degrade. Because the keys can be pressed in flush, the unit
easily wipes clean with a shop rag. With a rubberized housing, aluminum
block and brass valves hose parks and connections the 550 is one of the
most durable instruments Testo has developed.