Originally Posted By: jschwartz1 This post was automatically imported from our archived forum.
Benjamin:
Welcome to the board. You can find a lot of these questions by going to the search box. Type in some keywords and you will get your answer quite quickly.
To answer your question, you would measure the temperature difference between the return air vent and the closest vent to the air handler.
Lets say the return vent measures 75 F and the air vent measures 58 F.
You would have a difference of 17 F. Generally you want to see the measurement to be between 12-18 F. A lot will depend on the current outside temperature and humidity levels. DO NOT under any circumstances operate the A/C if the outside temp is below 65 F.
You can measure the temp using a mechanical probe or a fancy infrared laser. The infrared can be used to measure hot spots in the electrical panel. You can pick one of these up between $99-149 or go to the local ACE Hardware store and pick up a digital mechanical probe for $20.
If the temperature differential falls below 12 F, recommend a licensed HVAC contractor make a further determination of what needs to be done.
Don't assume its just a freon issue. It may be a compressor, dirty coils, restricted air flow, etc.
Originally Posted By: Gary Reecher This post was automatically imported from our archived forum.
As said lots depends upon the humidity level. The higher the humidity level the lower the temperature drop as the unit is removing most of the heat in a latent form. As the humidity level drops the temperature drop will increase. The air conditioning also needs to operate continuously for at least 10 minutes to stabilize. Then take your temperature checks. Preferrably measuring at the duct entering the air handler or furnace and immediately after. Measuring temperature differences at the return air grill and supply register is inaccurate. One being that if the suppy ducting is uninsulated the metal ductwork must cool down. As jschwartz1 said if temperature drop is less than 12 degrees call a repair company. In the same regards if the temperature drop is greater than 20 degrees call a repair company as this is an indication insufficient air is flowing through the cooling coil and liquid refrigerant could very well be returning to the compressor. This will cause premature compressor failure.
Originally Posted By: dbowers This post was automatically imported from our archived forum.
Benjamin -
As a Mechanical Engineer with a major in HVAC - measuring your TD (temperature drop) at the A/C coil area will tell you if the unit is doing what its supposed to - BUT - many times it will be doing exactly what its supposed to be doing at the unit, and still not have a good TD in the habitable rooms of the house (the place you live).
I measure the RA and SA at the registers 1st. If its bad there I measure the TD at the unit to see if my problem lies in the AC unit or the ductwork between there and the rooms.
Originally Posted By: tallen This post was automatically imported from our archived forum.
My Mothers AC guy. Takes his temp prob and sticks it in the register. He say’s if it get’s to 48 degrees F within 5 minutes all is good. Is this correct?
– I have put the past behind me,
where , however, it now sits, making rude remarks.
Originally Posted By: lkage This post was automatically imported from our archived forum.
Gary Reecher wrote:
As the humidity level drops the temperature drop will increase. The air conditioning also needs to operate continuously for at least 10 minutes to stabilize. ... if the temperature drop is greater than 20 degrees call a repair company as this is an indication insufficient air is flowing through the cooling coil and liquid refrigerant could very well be returning to the compressor. This will cause premature compressor failure.
-- "I have never met a man so ignorant that I couldn't learn something from him."
Galileo Galilei