Readings

[pentond1]

When carrying out maintenance on air conditioning units is it a requirement to fit gauges or would calculating superheat using temperatures be sufficient. What are the maximum/minimum LP - HP working pressures associated with 407C and 410A. At what intervals should the HP trip be tested.

[Brian_UK]

How are you going to calculate superheat using just temperatures?

[El Padre]

Hi,
I would not personally put gauges on a system unless I suspected a problem, especially since the introduction of 410A and the possibility of CO2 VRV's.
Most chillers and VRV's are equipped with sensors and transducers that can give you all the readings that you need, on splits I log air on/off temps, coil sensor temps (where possible) and the usual running current etc.

[Scramjetman]

A lot depends on what the service contract calls for. Some service contracts insist that gauges be fitted and readings taken.

If superheat is to be calculated, you will need to fit your gauges and read off the suction temperature ( close to the evaporator) and then measure the pipe temperature at the same location - much like what a TX valve does. Subtract the suction temp from the pipe temp and voila! the result - that's the superheat. You can't get this superheat temp without knowing the suction temp at the same moment as the pipe temp is taken so gauges must be fitted.

It's a good question though. If the contract doesn't call for it should we bother. I see two important points.

1. If the TX is getting a bit dodgy ( or someone's messed with the superheat settings on the TX - it happens... ) , and the superheat is starting to wander away from where it should be, the only sure way of picking this up is to fit gauges and calculate superheat. An alternative I suppose is to fit a coil temp sensor - but its accuracy can be a bit questionable. This surely saves a compressor from early destruction if it is detected. And the whole concept of servicing is to detect problems before they become terminal to the plant or expensive.

2. Each time gauges are fitted, an opportunity exists to introduce moisture and contaminants (including air) to the system and refrigerant is lost in small quantities each time this occurs.

To me compressors are worth a whole sight more than the occasional refrig top-up and the system dryer should catch any trash entering the system. I'm all for checking superheat each time.

[marc5180]

When carrying out maintenance on air conditioning units is it a requirement to fit gauges or would calculating superheat using temperatures be sufficient. What are the maximum/minimum LP - HP working pressures associated with 407C and 410A. At what intervals should the HP trip be tested.

I don't fit gauges when carrying out maintenence unless there seems to be a problem with the system, the same goes for superheat/subcooling readings.

Take temperatures at the individual points around the system and you should be able to tell if you have a problem or not.

Working pressures on R407c can range from 0 bar to 25 bar ( roughly )
Working pressures on R410a can range from 0 bar to 36 bar ( which is normally when your HP switch will knock the system off)

Both the Lp and HP should be tested at regular intervals, if its minor service then i wouldn't test them but if its a major service say every 3-6 months then i test them.

Hope this helps.

[pentond1]

I believe on some maitenance routines temperatures measured at various point of a running system are being used to calcultate the theoretical superheat input output evap etc

[taz24]

I believe on some maitenance routines temperatures measured at various point of a running system are being used to calcultate the theoretical superheat input output evap etc

A very crude way of doing it is to measure the temp of the pipe into the evap and the temp of the pipe out of the evap and this will give you a temp differerance.

But it is very crude and suseptable to lots of other factors.

With a split air conditioning unit, the expansion starts in the outside unit so theoreticaly you could measure the supply pipe and the return pipe and you will have a temp differance between the two.

But I must hasten to say this is not a measurement of actual superheat it is a measurement of the differance between the two pipes.

taz.

[pentond1]

Thank you this puts a good case for fitting gauges as ensuring system is running at optimum efficiency also helps to reduce wasted energy. With On another matter. with this in mind

[pentond1]

Sorry for the last bit pressed wrong key previous post. With efficiency in mind what are the recommended superheat readings for R22, R407C, R410A.

[Burrah Boy]

Generally between 5-7K. For R407c has a high temp glide, so dew point is used for start of S/H. Use a comparitor.

[pentond1]

If I take the LP pressure and cross reference this using the slide rule Pe (Bar) scale for the Deg C vap and measuring the temperature at the tev sensor bulb Deg C by taking one from the other will give the superheat value K, what value should this be for R407C.

[nike123]

If I take the LP pressure and cross reference this using the slide rule Pe (Bar) scale for the Deg C vap and measuring the temperature at the tev sensor bulb Deg C by taking one from the other will give the superheat value K, what value should this be for R407C.

You should buy dedicated gauge for R407C which has dew point temperature indicated at low pressure gauge and bubble point temperature indicated at high pressure gauge. That way you could simply calculate superheat and subcooling as usual.

[pentond1]

Many thanks will look to purchasing these gauges - what superheat temperature should I be looking for.

[nike123]

Many thanks will look to purchasing these gauges - what superheat temperature should I be looking for.

Standard evaporator superheat of about 4-5K