Using measureQuick to Identify a Suction Line Restriction

Identifying suction line restrictions is a tricky task as many of the symptoms are similar to charge and airflow issues. In this video Jim shows you the symptoms of a suction line restriction and how measureQuick can quickly identify the problem during the normal testing process.

[@Seedavis397]

I’ve always been amazed at how much it takes for a suction restriction to be obvious

[@measureQuick]

Us too.

[@emailfilters]

I am so glad to see this added to mQ! Only 20 minutes ago I was watching an acservicetech demonstration on troubleshooting ac systems. He showed pressure responses to air flow restrictions (cond. and evap.), liquid line restrictions, an overcharge and an undercharge. As I watched, I wondered what I would see with a suction line restriction. Thank you, Jim -- perfect timimg!

[@AG-tg9in]

I swear I thought I was the only one doing the same thing but in my house and experiment on measure quick. Good video Jim as always. This is a perfect help to anyone interred in the trade 👍

[@jericosha2842]

Wow this was very helpful. Thank you sir, appreciate you making us better technicians for free. God bless.

[@redmanaaron97]

Excellent research and development!

[@lee-johnson]

Good test for suction filter drier. Which shouldn’t be left in the system but they are. thank you Jim

[@jaysonhines1]

Nice add on Jim, thank you. The only other awesome thing to observe maybe, would be an Amp clamp on compressor simultaneously.

[@CHOMAHOMA]

GREAT. I only use mQ. I have spent a lot of time just watching it, going back and forth, comparing measurements, and I still have way more to learn and time to spend with the software in order to put everything together and advance.

[@aab9996]

This is great, I had this issue in 1966, took 2 hours to track it down

[@brianmcdermott1718]

❤Great info. Thanks Jim.

[@deseani1]

Next level. I have to look at this again

[@jamesfitzsimmons381]

Jim it fair to say that anytime the suction line temp at the condenser is colder than it is leaving the evaporator coil it’s a suction line restriction if you started with a proper refrigerant charge. I’m looking at shorter diagnostic time w/o following the SH anSC thanks

[@measureQuick]

Agreed, however that is not a common set of measurements that most tech do during regular service. I would have found it by sound first myself, then verified it with two clamps.

[@jamesfitzsimmons381]

@@measureQuick Thankyou for your time

[@kbouwman64]

@@measureQuick I have started measuring line temperature changes to my workflow. I started on a day when it was over 100 degrees and found suction line temps rising 30 degrees due to bad or missing insulation. I work on bulk milk tanks where the tanks are typically bulk headed in an outdoor wall. This puts the evaporator connection outdoors. In winter, this evaporator line will be going out into -20F ambient conditions and I would assume there might be some desuperheating in the suction line between the evaporator outlet (which is the EEV superheat control point) and compressor (which is indoors) inlet. Might this new suction restriction algorithm flag this as a restriction?

[@staticpressurenerd5182]

Very cool Jim, very cool. 😎

[@frankmashione139]

Thanks for the video

[@MinnesotaHvAc]

Once I had the system start and run normally. Then the low side equalized with the high side pressure. So the only thing I could figure was a restriction in the condenser from the service valve to the compressor. So I pulled the new condenser and installed a new one.

[@kennethnapier131]

In the past I diagnose suction line kink with listening to the suction line, that kink and that refrigerant rushing by travels

[@measureQuick]

The sound is a dead giveaway. I built it into the app for the hard of hearing.

[@HVACRTECH-83]

Very interesting, in over 20 years never come across this situation

[@measureQuick]

I have seen 2 in 30 years, pad settles in new construction. We have basements so it can easily happen. If you are working in attics I would guess it would be a lot less common. We built it in as it is hard to diagnose.

[@coldfinger459sub0]

It would be Excellent to add some site glass before and after the ball valve. Site glass immediately exiting the condenser another side class just before the expansion valve. And while the system is down for servicing might as well add a cycle class immediately before suction line entering the compressor in another side glass immediately leaving the evaporator. Catch on video phase change along the lines during different operating conditions in severe scenarios.

[@measureQuick]

That is a good idea.

[@aycabbas]

Nice, can you make the same test with measuring pressure at coil and condensunit, if you have pressure drop more than normally, then you have an restriction or small suction pipe select.

[@measureQuick]

There was a substantial pressure drop much more then the 2-3 psi typical. It is hard to see though because the pressure is only measured at one location.

[@marconantel7735]

What effect did it have on air temps I wonder? And the sound, while clear at the source, I wonder how obvious it may be on a 30-50 run ?

[@brianf2401]

Just curious-it doesnt seem to flag anything when you use your discharge clamp on your suction line even tho it is still mapped that way. Not sure exactly what having a 59° discharge would indicate but I would have expected it would be a flag of something being wrong? Or did you unmap it when you used it?

[@measureQuick]

We typically look at the entering suction superheat and the maximum discharge temperature as a guideline for proper operation. Copeland will tell you the max temperature for oil breakdown as well as the ideal suction superheat. There is a range listed for discharge line temperature, but if the actual compressor is known, the precise temperature can be calculated. I suppose since we can determine stable operation we could look at min and max for discharge temperature.

[@williamlongo4819]

Hi Jim. I have a field piece VP87 vacuum pump that always trips gfi receptacles. I returned it and got a replacement and it still trips the gfi as soon as I flip the on switch. Any ideas? Have you had this issue? Thanks. Bill.

[@measureQuick]

Have you tested it in another GFCI?

[@williamlongo4819]

@@measureQuick Yes at multiple houses. Im thinking its got to do with the DC inverter since my last pump was an AC pump and i had no issues. That is the only difference.

[@pat9096]

What percent did you close the valve? Always curious about how much of a kink is to much? It looked like you were near 90% closed when you started to see anything?

[@measureQuick]

It is about 85-90% closed, but remember that it is a ball valve so it is not proportional. At 75% it is basically 100% open as far as not creating a significant restriction.

[@nickdaggitt5079]

Not completely relevant to this video, but i would really like the ability to nickname or custom tag each probe. It would make changing probe designations alot easier in the toolbox.

[@boywhohadatiger]

How do you think this condition would look on a heat pump in heat mode

[@measureQuick]

High head pressure for sure.

[@boywhohadatiger]

@@measureQuick I had a situation the other day on a Lennox heat pump where head pressure were climbing over 500 psi in heat mode noticed some compromised return ducts but my initial test of TESP with the filter removed proved around 0.37 with the filter installed and tested I was seeing 0.90 I recommended solving that first. But the lineset generating a very loud vibrating noise on the inside wall by the condenser when seeing high pressure. A part of me believes that suction line could be bent also but I couldn’t get a accurate cool check because ODA was under 65 (62 degrees) but when I did check I had low suction pressure about 100 psig but no High super heat it was about 10 and it’s a txv so that checked out imo. But I won’t rule it out just because of the excessive vibration. But I’m thinking airflow for my situation.

[@jrsmyth9761]

Did I misunderstand something on the diagnostic definition? How is the condenser inlet HOTTER than the evaporator OUTLET? His discharge temp clamp is 59° and the suction line clamp is 52°. Doesn't that make a 7° DROP/LOWER condenser temp and NOT a HOTTER condenser inlet temp? (He said 57° and 51°) Basically you are doing the same thing on the suction line that you would on the liquid line or filter/drier, checking for a temperature difference between 2 points. That restriction had to be quite severe to start to make any difference in more than one parameter before MQ could "see" it. It also still had a low refrigerant diagnosis as an option, so be vigilant.

[@measureQuick]

It is hotter on a properly operating system. For example 12 degrees of evaporator superheat and 15 degrees of total superheat. You are correct, the restriction has to be pretty bad for it to be evident with only a single probe at the condenser inlet. The takeaway is to listen for it because you may hear it before anything.

[@jrsmyth9761]

@@measureQuick Watch the video from 7:54-8:17. does what you say match the MQ diagnostic box? I think the box writing is the opposite of what you say.

[@seek3n]

Isn't discharge line is inside the condensing unit?

[@measureQuick]

Yes, we piped it to the outside to create faults.

[@kylecarman4809]

I’ve ran across a few systems with low superheat and low subcooling after verifying airflow. Typically on hotels. So the main point is comparing temp readings at outlet of EVAP and inlet of condenser on suction line, and if the line temp is colder at the inlet on the condenser than the outlet of the EVAP, then there’s a possible restriction? Because we ‘should’ be gaining/picking up SH the closer we get to the condenser, not losing/dropping in SH, right?

[@measureQuick]

Yes, you are correct. Restriction or floodback. One of the two.

[@kbouwman64]

You will only gain SH if the suction line is in a warmer environment than the refrigerant inside the suction line. While this is likely for a residential air conditioning application, for refrigeration applications, that is not at all a safe assumption.