What I would tell you about the three splits you have listed is that you have 3 identical systems 14 degree split. All three units are transferring exactly the same temperature from the air circulated across the A-coil to the freon being circulated in the A-coil. The return temps you listed as 78 84 & 90 and the supply temps of 64 70 & 76 simply means nothing or that someone just started the A/C unit on a hot house. What means something is that you have 14 degrees of capability of transferring or removing heat from the home to the exterior and if you set the thermostat on 70 degrees it will eventually reach set point just takes a longer run time to get there
:roll: Ok guys here we go I am going to spell out what I do as an Hi to inspect a A/C system and why I do what I do. I am not a PE or anything close but I have been working in this field since mobey dick was a minnow.
With the unit running I take the temperature from the registers and the return air temp as my very first item. Why because I don’t care what the temp at the discharge from the A-coil is at this point I want to know what the temp is that is available for cooling the home. Its called duct loss between the coil and the registers more duct loss in the attic than in the floor due to extreme temperatures makes sense to me. I check for air volume at the registers and if I have a good TD between the supply registers and the return air 16 to 20 with good air volume I store this in the memory bank until we view the furnace and ducts if they are in the attic or in the crawl space.
I check visible wiring in the furnace for evidence of burnt wires. I view what ever part of the heat exchanger usually just the bottom for rust build up and I check the flame in heat mode for color and roll out on the older type of open burners. I check the blower wheel for lint build up as this will tell me if the A-coil is matted over with lint. I perform a CO test on the heat exchanger if present.
In this area with ducts in the slab I look for signs of water in the ducts. With ducts in the attic or the crawl space I want no bare metal showing and If flex is used I want to see no inner lining. I Check for air loss where the ducts connect to the plenum and for separated duct any where between the plenum and the registers. The return ducts if used should be completely sealed I do not want to draw in any un-conditioned air. The suction line should be insulated especially above a finished wall.
The condensate drain line should not be hard piped to the sewer main (air gap required) and it does not matter if there is a P-trap installed or not if it is hard piped to the sewer line you will get sewer gas into the air stream on a up flow furnace because the water will evaporate from the trap in the heat cycle. If the furnace is installed in a attic it is required to have a secondary drain pan under the coil with a secondary drain that enters a visible area from the ground level.
On electrical furnaces and strip heat on heat pumps I use a amp meter to ensure all of the multiple strips have amperage draw with the stat in the high position just in case there is a two stage stat for bringing on all of the strips.
I check the name plate data for tonage and age and the MFG’s recommended breaker size and ensure that the breaker size has not been exceeded or undersized. I check the condenser fins for lint build up and physically touch the suction and liquid lines at the unit while casually checking the size of these lines.
I do not consider this as an in depth or micro evaluation of the system. Checking TD at the registers has served me well as a HAVC person and as a HI I don’t think I will be changing my mind in the near future.
RR you need to close all of the windows and doors if you are getting TD’s as described above;-)
Re. the kitchen faucet leak escalade - that has got to be the funniest thing I have read all day - Russel, you have GOT to put out a book! You’ve got some talent! Do you mind if I steal it for a good laugh at one of the NCT seminars?
Ever so true. There are various reason for “taking splits”, but none of those reasons have much to do with a home inspection. I take 'em, too, but I have other reasons than most do.
Air conditioning is a very involved science, and one should not attempt to derive very much information from one or two particular sets of readings. A home inspection should only indicate the unit was working at the time of the inspection. If one wishes to run the unit for a length of time to cool the house during the inspection, fine–but do not make any more of that than is necessary.
If one were to read how an air conditioner actually operates, I think the average HI would not believe it. It does not operate as one might think. “Hot” is used to cool, and “cool” is used to heat…which leads to that really neat invention–the evaporative coil. It’s where the evaporation takes place that is so astonishing.
So if one is not truly versed in the field, it is best to mess with it as little as possible.
Jae, try not to make more out of it than there really is. Compress a gas or liquid and it gets hot, evaporate a liquid or expand a gas and it gets cold. When you think about it, it is quite simple. If it was as complicated as many here make it out to be, it would cost a lot more to buy, operate, and maintain. You can’t swing a stick here in AZ with out hitting an HVAC guy.
I wanted to expand on a statement that I made concerning the checks that I perform on the older type gas fired furnaces. I stated that I do not check the limit switch. What I should of stated was I do not check the high set point of this switch by turning off the fan blower and checking what temperature this switch opens at thus shutting down the gas valve. My checks are all performed strictly by operation from the thermostat.
What I do check concerning the limit switch is premature opening of this switch during normal operation. This switch normally opens in the area of 200 degrees at the heat exchanger. I usually average 2 to 4 furnaces a year that the limit switch is malfunctioning and this is determined by simply observing the furnace to ensure the burners are not cycling on and off before the set point of the thermostat is reached. This is something that I consider very easy to overlook and is probally missed by many inspectors.
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Sounds like you’re talking about “short cycling.” By the time the Clients have told me that it’s too hot, the furnace has been running about 20 minutes or so. If it’s short cycling, one will know within 5-10 minutes, usually much sooner, so if the furnace cuts off without me turning it off, I check to see if someone has turned it off rather before asking me or telling me that it’s too hot. If it’s still on but the temperature is not the 98° that I set the thermostat at, then I probably have short cycling occurring.
I wrote about the way reporting on “a leaky faucet” has evolved over the years, as we attempt to better protect ourselves. However, I heard it first in a seminar given by Bob Pearson, of Marion Allen Insurance. The story has the virtue of being funny, very real, veryu serious, and very educational. P.S. I’m trying to persuade Bob to do a seminar with me on avoiding litigation for NACHI, and hope he’ll take me up on it. It’ll be interesting.
Brian, I posted a question on another thread you authored:
You, nor anyone else attempted to answer this “Simple” question.
Why. was it too SIMPLE?
The fact of the matter is that HVAC is so damn backwards (as Jae posted) that few (to include seasoned HVAC Vets) understand the true operation of what is really going on.
If you would like to stick to this thread, how about explaining the simple process of “Dynamic Loss” or the effect of “Apparatus Dew Point” on the temperature split. I would like to expand this subject to cover the Sensible Heat Factor and By-pass factor of evaporator coil design and a few other simple processes that apply. But, that subject may be too elementary and bore too many folks to discuss!?
David Please
Let the sleeping dog lye you are getting to deep for this board
I do not consider Hvac as backward,scientific or complicated just a simple pressure/temperature releationship.
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Point being how many inspectors stay in front of the furnace to determine this. If the burner cycles on and off enough it will eventually reach set point of the stat.
The anticapator has notta to do with cycling the burner unless set point was reached as they were designed to do exactly as their name indicates. (Anticapate) Energize the gas valve approximately 2 degrees below set point. If you have a burnt out Anticapator you will have no flame the gas valve will not open.
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If it was as complicated as many here make it out to be, it would cost a lot more to buy, operate, and maintain. You can’t swing a stick here in AZ with out hitting an HVAC guy.
