PSI not registering on Digital Gauge on Suction Side.

TCTOPPS

I have an AutoOL LM120. ...Yes inexpensive. It is not reading psi from the suction side when A/C is operating on my recent install of Goodman Heatpump. It is giving very low readings of 8 psi. I have 275 psi on the small tube liquid side. Subcooling is 8 degrees. Superheat is 125 degrees F. The suction temperature is 40 deg F. Liquid line is temperature is 80 degrees F. Is doing great cooling the areas. R410A refrigerant. Wondering why that is. Anyone have an idea? Thanks.

Does this AutoOL LM 120 guage fit my needs or is it missing features?

EdTheHeaterMan

I'm not familiar with the AutoOL LM 120 gauge but my guess is that 8PSI is incorrect. Is the fitting that connects the gauge depressing the Schrader valve? If the valve core does not open, then you will not get a pressure reading of what is inside the suction line.

Do you have an old school manifold gauge set to verify that the valve is opening when the gauge hoses are connected?

mattmia2

Is the entire evaporator getting cold?

TCTOPPS

EdTheHeaterMan, I have low-loss Yellow Jacket hose and fittings at the condenser valves. I used Appion fittings to do the vacuum. The system was precharged for 15 feet. So I broke the vacuum with the precharged. But I think when adding additional refrigerant is used just the gauge. As it did fill to get SubCooling up to 8 psi. So I assume it opened. But would that have been the refrigerant tank pressure pushing the Schraeder valve to open on the suction side?

TCTOPPS

mattmia2, I will have to check the evaporator tomorrow. The building has really cooled down quite well.

mattmia2

Are you sure the gauge isn't set to some weird mode or was zeroed under pressure or something?

TCTOPPS

mattmia2, I will check in on that too. I may have zeroed it. But I turned it off and on too. It has a410R setting.

mattmia2

does it have to be at atmospheric pressure when you turn it on? do instructions exist for this?

TCTOPPS

mattmia2, Minimal Instructions, I could do a calibrate test before I hook it back up again.

mattmia2

it should read 0 psig when nothing is hooked up to it

TCTOPPS

mattmia2, True, I had a suction line hooked up.

pecmsg

What do you hope to gain by gauging up?

EdTheHeaterMan

pecmsg said:

What do you hope to gain by gauging up?

Sounds like a new install... Obviously @TCTOPPS is attempting to read the super heat and the sub cooling as would any refrigerant tech. But if there is 100+ psi in the suction line and the gauge is reading 8 PSI, then your super heat calculator in the gauge set, will not be correct. As he stated the Super heat is 125°. but the suction line is "Bear Can Cold". Something is not right. either the gauge is defective or the pressure is not reaching the gauge from the line set connection.

As far as the Schrader valve being depressed by the refrigerant pressure, that is unlikely.

In order to check if your gauge is defective, you need to use a "Known Good" gauge and then byy the proces of elimination you can find the problem. is the valve depressing insert of your hose missing? is the gauge defective? Is the Schrader valve core defective. There are so many options to list, but I'm just too lazy to think of all of them. Start with a "Known Good" gauge and go from there. You may even need to do the math yourself with a analogue gauge and a calculator. Do you need the formula?

LOL. Mr. Ed

mattmia2

You can always connect the high side gauge to the low side and see what it reads. ( YOU CAN'T CONNECT THE LOW SIDE GAUGE TO THE HIGH SIDE).

EdTheHeaterMan

mattmia2 said:

You can always connect the high side gauge to the low side and see what it reads. ( YOU CAN'T CONNECT THE LOW SIDE GAUGE TO THE HIGH SIDE).

Not necessarily. You CAN connect the low gauge to the liquid line. The hose connections are identical! LOL

That could be what happened to that gauge, and why it "no work so good" now!

mattmia2

It also isn't clear that the low gauge in the off brand Chinese manifold set is more sensitive than the high side gauge like it is in a quality manifold.

TCTOPPS

mattmia2, I have checked Schraeder ports by removal and use of Appion valve fittings. Same results. Checked evaporator coil. It was cool all over. No frost or frozen areas. There are two pages on guage for Ev and Co and also SH superheat and SC subcooling. Temperature is lower today and SC Temperature on guage is around 6 F . Yesterday it was close to 9 F with the second stage running. I am reading that the PSI on a410R condenser should be a range of 100 psi to 140. What should it be? I understand that this is a relative number as we are concerned with temperature. My temperature numbers seem to be close to required. I am hesitant to jump to faulty reading on gauge. But what could it be then if not?

TCTOPPS

pecmsg, I want the satisfaction that I am getting the correct info from the equipment and that the system is set up correctly.

TCTOPPS

EdTheHeaterMan, Thanks, Yes, Sure the formula! I have attached the proper tubing and hookups. I use charts and software when available.

pecmsg

TCTOPPS said:

pecmsg, I want the satisfaction that I am getting the correct info from the equipment and that the system is set up correctly.

Pressures without temperatures are worthless.

Gauging up releases a small amount of refrigerant each time and is a bad practice.

Are you even licensed to hook up gauges?

TCTOPPS

Would TXV valve need adjustment? First I want to establish what the problem with PSI is about.

TCTOPPS

pecmsg, Thank you, I use low-loss hoses. Completely solves the problem of loss as only a dismissable amount is released. Obviously, draining all hoses into a low-pressure suction line via the manifold at removal only improves upon this strategy.

TCTOPPS

So this guage is faulty as I have checked the PSI by switching low side measurement to high side. It reads about 115 PSI now. That is good to know. But remaining is my dissatisfaction with so much of the less expensive equipment. I am going to replace it with Fieldpiece digital I think. Any suggestions? Thanks.

pecmsg

So what does that reading tell you?

TCTOPPS

pecmsg, That the inexpensive gauge is going to be replaced. LOL. I like the function of digital that does the work for me. I am reading about Fieldpiece over Testo. Although both are well-liked. The 115 psi tells me that there is nothing strange going on with the line set. The other information just confirms it. I am going to get new information from a better digital gauge because of concerns for computational accuracy. Thanks for your interest.

mattmia2

does the low side gauge read vacuum when it is open to the atmosphere?

EBEBRATT-Ed

How can you have 125-degree superheat with a 40 deg suction line? Is that a typo? Do you mean 12.5 deg superheat?

mattmia2

EBEBRATT-Ed said:

How can you have 125-degree superheat with a 40 deg suction line? Is that a typo? Do you mean 12.5 deg superheat?

if you have a gauge that reads 100 psig low and you just look at the table without understanding what is happening you calculate a 125 degree superheat but if you know 8 psig is about 40 below you know that isn't actually happening.

EBEBRATT-Ed

@mattmia2 got it

pecmsg

TCTOPPS said:

pecmsg, That the inexpensive gauge is going to be replaced. LOL. I like the function of digital that does the work for me. I am reading about Fieldpiece over Testo. Although both are well-liked. The 115 psi tells me that there is nothing strange going on with the line set. The other information just confirms it. I am going to get new information from a better digital gauge because of concerns for computational accuracy. Thanks for your interest.

and how does one reading tell you that?

All the 115#'s tells you is the saturation point of that refrigerant is 38.3°F. Now you need the temperature to tell you super heat.
If it's an X-valve than Sub cooling #'s are required.
You'll also need CFM reading of the indoor fan.

ChrisJ

You need to check the ranges of the gauges, but when I did my install at home I had bought a brand new set of Yellowjacket liquid filled gauges to add to my manifold. To my amazement, besides the TXV issue I was having, my new high side gauge kept sticking. So, there I was with a TXV hunting all over the place and my high side gauge wasn't showing it. Lot's of fun.....

In my case, I was able to use the lowside gauge on the highside.

You may be able to use your high side gauges on the lowside, but you need to see how low it can read, and how accurate it would be at those pressures.


Just because it's wrong, doesn't mean it won't work (swapping gauges etc) but you need to know what you're doing and proceed carefully.

As other's have said, if your lowside gauge isn't working right, then your subcooling and superheat readings are 100% incorrect and mean absolutely nothing.

pecmsg

ChrisJ said:

You need to check the ranges of the gauges, but when I did my install at home I had bought a brand new set of Yellowjacket liquid filled gauges to add to my manifold. To my amazement, besides the TXV issue I was having, my new high side gauge kept sticking. So, there I was with a TXV hunting all over the place and my high side gauge wasn't showing it. Lot's of fun.....

In my case, I was able to use the lowside gauge on the highside.

You may be able to use your high side gauges on the lowside, but you need to see how low it can read, and how accurate it would be at those pressures.


Just because it's wrong, doesn't mean it won't work (swapping gauges etc) but you need to know what you're doing and proceed carefully.

As other's have said, if your lowside gauge isn't working right, then your subcooling and superheat readings are 100% incorrect and mean absolutely nothing.

The OP still hasn't answered Is He / She licensed to gauge up?

EdTheHeaterMan

pecmsg said:

The OP still hasn't answered Is He / She licensed to gauge up?

Does the 5th amendment apply to EPA test applicants? And do you know if the OP is a he or a she? You are making assumptions that non binary individuals can't pass the test! Be careful in this new age of all acceptance of all persons of all persuasions

You could end up here:

pecmsg

EdTheHeaterMan said:

The OP still hasn't answered Is He / She licensed to gauge up?

Does the 5th amendment apply to EPA test applicants? And do you know if the OP is a he or a she? You are making assumptions that non binary individuals can't pass the test! Be careful in this new age of all acceptance of all persons of all persuasions You could end up here:

So

what does 115 PSIG tell you as far as what’s going on?

ChrisJ

@pecmsg



All I saw was them give SC and SH numbers even though they think their low side gauge is broke. Based on that.......

JUGHNE

IMO, I think anyone's first set of gauges should be old school analog.

Do we still teach children to tell time on an analog clock with hands or just look at a digital read out?

TCTOPPS

We were able to get a reading of 115 PSI low-side suction line by switching lines to measure with the high-side liquid line of the digital gauge. I am satisfied that this is more likely a normal pressure on the low side. But I am only guessing based on the other information which I am now not confident. So, I purchased probes from Fieldpiece. I hope to have better information soon. As stated by others, I may have skewered readings that do not give correct accuracy.

Noted:

Pressure tested to 450 psi without decay overnight. Vacuumed to 195 microns with decay to 240 microns which held for 30 minutes.

Condenser was precharged to 15 feet. The line set was 28.5 feet. A requirement of 13.5 feet at .74 ounces per foot is needed with 3 additional 90-degree bends at 2.6 ounces each. Cooling was effective immediately without any additional refrigerant.

(But 'we' are looking for maximum efficiency and equipment longevity NOT 'beer can cold.' LOL! Using the euphemism 'we' for 'me' could be considered a binary. The team around here is more than just one individual which also includes my significant other. In this case, however, appropriate city inspectors are involved in building permits! So then, a non-binary perspective would be more appropriate! LOL!)

It is a simple process to open up valves on the condenser/heat pump with Appion Schraeder valve removal tools. With Yellow Jacket low-loss hoses, it worked famously to attempt testing with faulty digital gauge.

Thank you for the insights as each have been helpful. Great!

TCTOPPS

mattmia2, The low side reads a very low number. It will zero out and read zero at atmospheric pressure. Basically, it is not functioning. It seems the other readings are 'in the ball park' but if the computation is skewered because of this faulty readings ...Then all considerations for other readings I think are wildly speculative.

TCTOPPS

EBEBRATT-Ed, Thanks, I read into the comments in this thread accurate info from what appears to be at least a partially misfunctioning digital meter. More to come as I am getting additional equipment from Fieldpiece to recheck the system.

ratio

You don't need to add in any charge for fittings. The 'length' specified for e.g. 90°s is only used for pressure drop calculations. Typically, I'll just cypher up the adder for the liquid line, that way I'm certain to be adding when I dial in the charge instead of recovering.

ChrisJ

JUGHNE said:

IMO, I think anyone's first set of gauges should be old school analog.

Do we still teach children to tell time on an analog clock with hands or just look at a digital read out?

2 out of 3 of my kids can read analog clocks with ease.

The third isn't a year old yet.......I think she deserves a break on this.

I don't know what "we teach" but that's what I teach.