Thread: Need temperature probes for HVAC testing

I've been using Taylor water-resistent units but the last few have been defective (could not calibrate). Looking for something better. Suggestions?

Originally Posted by Randall Clark

I've been using Taylor water-resistent units but the last few have been defective (could not calibrate). Looking for something better. Suggestions?

I had to Google Taylor water resistent etc.. I had no idea what it was.

If you are talking about taking the temp in the supply plenumn try a simple digital cooking thermometer. Last one I bought was around $7 at WalMart.

I stop taking Delta-T readings several years back. I only take temp readings now to confirm what I have found.

Taylor thermo--- Taylor USA | Thermometers - Restaurant & Hospitality

I use UEI PDT 550's. Keep the cooking thermometers in the kitchen.

I put one temperature probe in the supply line,and one in the return,and the temperature difference should be about 20 degrees different,this indicates the system operates is operating properly.

Fieldpiece makes nice hvac testing equipment, you can also usually find some of their stuff on ebay.

When I went through HI training back in the dark ages I was told to look for a delta temperature of 12 -18 degrees F as in an indicator of proper AC function. I don't remember ever seeing that written down anywhere though. If I had to support that claim where would I find an authoritative source?

Originally Posted by Marshall Brown

When I went through HI training back in the dark ages I was told to look for a delta temperature of 12 -18 degrees F as in an indicator of proper AC function. I don't remember ever seeing that written down anywhere though. If I had to support that claim where would I find an authoritative source?

I was told 13 to 23 degrees in my training, but the HVAC guys say that using a TD isn't reliable, and not to use it. I still do, and if it falls outside my 13 to 23 degree guidelines, I report that the A/C may not be functioning as efficiently as it should, and recommend further evaluation and correction as needed by a qualified HVAC contractor.

One of the guys I trained with was using magnetic temperature probes that stuck tight to the plenums, and didn't always want to slide out of the access holes. Does anyone know where I can find some of these? Most of the thermometers I get from an HVAC supply house are crap, but I eventually end up leaving them in the plenums, and can't justify spending a whole lot.

Originally Posted by Harry Janssen

I put one temperature probe in the supply line,and one in the return,and the temperature difference should be about 20 degrees different,this indicates the system operates is operating properly.

A temperature differential from return to supply is not an indicator that the system is operating correctly. You would need to calculate either the superheat of the the unit or if it has a txv the subcooling. If you want to know if the system airflow is correct for a properly charged system you would need to measure indoor drybulb,indoor wetbulb and the evaporator dry bulb and do the calculation. Also you need to know the refrigerant that is being used because of the different cooling properties. Unless you are trained and certified to work on HVAC I wouldn't make a statement on a systems operation other then it was working or not.

Bill K
Nationally certified Test And Balancing technician

Originally Posted by BillKace

A temperature differential from return to supply is not an indicator that the system is operating correctly. You would need to calculate either the superheat of the the unit or if it has a txv the subcooling. If you want to know if the system airflow is correct for a properly charged system you would need to measure indoor drybulb,indoor wetbulb and the evaporator dry bulb and do the calculation. Also you need to know the refrigerant that is being used because of the different cooling properties. Unless you are trained and certified to work on HVAC I wouldn't make a statement on a systems operation other then it was working or not.

Bill K
Nationally certified Test And Balancing technician

What rules of thumb would you recommend be used to make the decision on whether or not to call for an HVAC contractor to make a full evaluation of the system? Remember as HI's we do not attach gauges but are expected to make an educated guess regarding the status of the system. I agree that the delta T should not be the only indicator but would like to have your input.