Review: Testo 550 Digital Gauges
This is my third installment in my DRSA reviews. I've been a fan and supporter of Testo products for a long time. I purchased my first set of digital gauges about 6-7 years back, the 2nd generation Testo 523. I had some issue with those but I enjoyed the setup and accuracy. So, when Testo introduced the 550 series - I was very excited. I purchased the 550 about 2 years ago. Being that I've had these for 2 years, I have a little more experience with this DRSA than with some of the others that I've reviewed.
When I opened up the box inside was a hard carrying case, the gauge/manifold apparatus, two pipe scissor clamps, and a instruction manual.
In removing them from the protective case, I first noticed the small compact size of the gauge/manifold. It is small compact and completely rubber encased. The small compact size allows the gauges to be hung or placed in numerous places when checking and servicing a refrigerant issue.
I really like the hard plastic carry case. The case is built strong and sturdy. I know, if some of you guys are like me - I won't leave them in the case. I will hang them up in the back of the van for easy access. But it sure is nice to have the option of putting them in the heavy duty case.
Turning on the unit, it has a smaller display than some of the other DRSA. But not smaller than a set of analogs. It comes equipped with a bright white backlight. On the top line, it displays pressures. On the second smaller line, it displays pipe temp, sat temp, or SH/SC. You will have to toggle the up and down arrows to scroll through the second line displays. The controls are very intuitive but some features require a little reading in the manual.
It has hose parks that swivel. So you can park your hoses in the front or in the back. Also, it comes equipped with a hanging hook. This is different than the usual manifold hook. It is thicker and can swivel up and down along with 360 degrees around. This hook has been an issue with the 550's. They break right at ball point. I'm currently on the my third hook. After the second one, I ordered 2 extra hooks and I will swap them out myself if they fail again. Testo did offer to upgrade the hook to the thicker hook like is found on the 557 and 570 but I would have to send them in and be without for a couple weeks.
Testo uses sealed proprietary thermistors for their pipe temp sensors. This provides much more accuracy than "K" type sensors which are subject to stray induced/EMI voltages. The two sensors plug into each corresponding side of the unit. This is one of my dislikes. They simply push in and do wiggle loose easily. Plus, you need to have the sensors hooked up prior to powering up the unit. If powered up without the sensors attached, it won't display any temps even if the sensors get plugged in after a power up. You have to cycle the power and then they will show up.
The pipe clamps jaw opening isn't very large. It looks like it will fit 1 1/8" pipe max. They do offer an additional Velcro strap that fit a pipe as large as 75mm (which equals almost 3"). One concern that I have is the way the wire is routed in the clamp. It kinda just hangs out there and looks like it has a high potential to get caught on something. I've also noticed that after some use, the metal sensor in the boot of the clamp likes to try to slide out of the grove. Not a big deal, just have to adjust the metal sensor every so often. Reaction time for the clamps is fast. It adjusts to any temperature changes quite nicely.
The 550's are equipped with a 580 psia low pressure transducer and a 780 psia high side transducer. Accuracy is +/- .75. This makes them fairly accurate but not the best on the market. Testo also recommends clearing hoses of refrigerant and zeroing out the gauge before each use. Sounds like a little bit of overkill but that's their suggestions.
The 550's have several modes. The snowflake mode which should be used for cooling and will calculate SH/SC conventionally. The flame is for heat pump and eliminates the need to swap hoses and probes and will calculate SH/SC reversed. The auto mode is when the snowflake and flame appear at the top of the display. In this mode, the 550 will automatically calculate superheat for the side with the lowest pressure and calculate subcooling for the side with the highest pressure. Speaking with the Testo rep, he suggested keeping it in the auto mode.
The gauges also come with a pressure drop test mode. When entering this mode, a delta P is displayed on the screen. It can performed two ways. Using the gauge only or using the gauge and OD temp probe (extra accessory). This is meant to be a longer timed test (from 1 hr to 24hr). During this test, the 550 measures intial pressure and temp and compensates for changes in pressure due to temperature. This feature can be very useful for leak checking newly installed systems.
Overall, a good solid accurate instrument. I've been a fan of Testo products and will continue to do so. They create accurate and useful instruments. I agree that some Testo tools may not be very durable but if you treat this instrument with just a little bit of care - I believe it will last a long time. Like I stated above, I've had these for two years and the only mishap was the hanging hook, which Testo's customer service took care of in a timely manner.
I created a list of good and bad features below.
1. Pipe clamp accuracy
2. Hard carrying case
3. Pressure drop test
4. Bright backlight
5. Compact size
1. Small display
2. Pipe clamp construction
3. Hanging hook
Once again, the good outweighs the bad. These are great accurate set of digital gauges. The 550's are more of an entry level option where as the 570 are more advanced. These gauges offer features that no DRSA can provide. I hope this helps someone in the market for a digital refrigerant system analyzer (DRSA) aka Digital gauges. Keep a look out next week for the review of the Testo 570 then many more tools in the weeks to come.
Brent A. Ridley
[Sorry for pictures being sideways. If someone knows how to flip them, let me know]