10 Degree separation

I have a friend that had an A/C installed. The tech did not strap the condenser unit to the slab, failed to install a place for the filter, and when we tested to unit’s performance we consistently got a separation of only 10 Degrees. Both times we tested the unit it was approx. 90 Degrees outside in the late afternoon. In my report I specified that there are many factors involved in the temperature differential but I felt that the 82-72 separation did not appear normal and an a/c professional should test the system. I instructed my friend not to run the unit without the filter and to have the tech out to strap down the condenser unit. Any thoughts on this scenario? He is closing today on this home and wants some more insight. I told him I would throw it out on the message board for expert analysis.


Why do you need to strap down the Condenser? They don’t strap them down here.

Every HVAC unit needs an accessible filter compartment. I see them missing once in a while and simply write it up.

If your getting a differential of at least 12 to 15 degrees, testing from the supply and then at the closest return vent to the air handler, the A/C efficiency is OK. You shouldn’t be basing your differential on outside weather.

If you’ve gotten an 82 to 72 degree differential, a lot of factors start to get involved.

How long did you run the A/C?

Give us the dates and time you tested so we can look up the weather.

Condensers should be strapped down in California because of earthquakes and in urban areas where they may get stolen! :slight_smile:

There are filter racks under the air handler and additional ones are installed at the unit where the duct attaches to the unit. Did you check there?

If you can give me the wet bulb temperature (as well as the dry bulb), I can tell you if the 10 degrees is OK.

That goes for anyone at NACHI. Get something to test wet bulb or relative humidity comming in and out of the unit and I will figure out how much the unit is reallty working.

Anything less than this is a WAG (wild a$$ guess). If you want a red face, be there when the HVAC guy shows up with a hygrometer.

I ran the A/C approx. 1/2 hour both times and the best numbers we got was what I previously stated. I only mentioned the outside temperature as an environmental factor so that all who viewed the post knew what the weather conditions were. The condenser unit should be secured to the slab as a safety preventive for the A/C lines in the event that the unit is accidentally moved. I am used to seeing an average of 15 Degrees on most units with the return temp at approx 60 Degrees on most units in similar circumstances as described. 72 Degrees after a half hour does not appear to be performing up to par. What is your take?

we make it mandatory that all ac units are strapped down in case of a hurricane and flooding

Due to our very temperate climate and little need for AC, we don’t have very many installed residntial HP/AC systems (although their installation is increasing). I have only looked at 2 this year.

In the first one (7 years old) the concrete slab the outdoor unit sat on has settled slightly towards the house. Due to operating vibration, the unit had slowly “walked” its way towards the house. Rigid copper pipe which was originally installed with 2 - 90 degree elbows now formed a perfect “Z”!! At what angle would it reduce refrigerant flow sufficiently to have the unit shut down on low/high pressure or rupture the pipe?

The second unit was only 6-7 months old but because of scrape marks on the level concrete pad, we could see that there was some vibration movement albeit small at this point.

The outdoor unit’s feet should be secured to to the concrete pad or other substrate!!

If the condensor is not level, the off axis tilt of the unit will cause it to move when the unit is running. Think of it in the same way as a helicopter. A helicopter will stay stationary until you tilt the rotor in one direction or another.

It puts a slight bit of stress on the line connections.

This may not be enough to deal with latent heat. Latent heat must be addressed first before the sensible temp will come down.

You should mention that. It is very important to me. If you didn’t post it I would have asked. Whoever said it wasn’t important …
Here in TN, units are sized for 95-98 degree “normal” air. If you exceed this, you will get numbers like your reporting.

Soft drawn copper can be moved and bent substantially without breaking. I think this is none of our business. Can you show a refrigerant pressure drop? Outside of your scope (EPA certification required)?

You may be right. But when you give me a dry bulb temp all I can do is take a WAG.

Who is “WE”?

This is the problem, not the unit not being strapped down. I call that “potential structural damage conditions”.

When I see the condenser changing axis pitch like a helicopter, I plan to run like hell because there is an earthquake happening. So your telling me that 1 inch pitch change in 7 years is going to make the condenser take off?

Come on guys, where is this coming from. I can come up with a better one. The grass cutting crew moved it! Or it was too close to the house and the HVAC guy got pissed off and moved it.

Lets bend some pipe and find out. Then we can change the HI standards and report this “evaluation”.

HVAC copper is stronger than plumbing pipe. If properly supported IAW mechanical standards I can hang on it! I don’t think a little pitch, settling, vibration is going to do all this stuff.

If the pipe is crimped, write it as crimped and fix. Don’t be making stuff up.

Wow you have seen two this year and both have moved .
Well I have looked at close to 100 and I saw no evidence of movement and some had a pretty good lean.
The only ones I have seen fastend where on angle brackets on the side of the home ( They all had damper pads to help stop noise vibration entering the home).
.I have taken some that where too close to the home to read the name plate and moved them out and put them back when done could see no noticeable bend in the copper.
I guess we are luckier in Ontario then down east.

… Cookie

Lots of other unknown factors to consider as well…Has the home been vacant without an AC unit running over the course of the summer to maintained. Often when I go into homes that have been vacant for some time w/o AC it will take hours for the AC to pull all the interior components down, plus like David said it will have to work like hell to remove all the latent heat (moisture/humidity) from inside. Those houses will start to pump water out the drain line like a water hose. Remember, everything we build houses out of basically absorb heat and humidity. Few people unless trained in HVAC ever think of the latent heat. They will typically come in, slap the thermostat on 60 deg. thinking it will make it cool off “quicker”. A half hour later it is just getting started removing heat. I routinely tell people not to raise their thermostats when they go off on vacation because any money they may have saved while it wasn’t running will get lost when they come home and try to get the house back into the human comfort zone. It can run non-stop for days to do this. Carpeting, walls, furniture, etc all have to be “re-conditioned”. The outside air temp and more importantly the outside humidity is very important to checking a system. Outside is where half the heat exchange is going to take place. What they taught us in HI school about HVAC could be written on the head of a pin and some of it was dead wrong! Johnstone supply has some good cheap on-line courses you can take to bone up on HVAC or take a course. The cost is small compared to what you can learn.

Something I see often, is the homeowner have painted all the rooms with water based paint to prepare the house for sale, shut off the AC, close up the house and forget about it. Meanwhile the water in the paint is evaporating like a big dog inside the house. Ive seen water running down the windows inside in sheets, puddling on the window seats. Mold, mildew and other nasties will grow like corn in places like that.