The AC System That Refuses to be Fixed

Contractor #1 said that the system would not cool at all if airflow was an issue.

Is he reinforcing #2's statement that due to insufficient airflow - the Evap Coil would freeze up? Have you watched it cycle & seen the coil freezing yourself during the cycle? getting to the air handler should not be a problem....

If he is confirming #2's appraisal - then maybe he should install the extra 3 outlets on his nickle

IMHO - bleeding & adding freon sounds like someone who doesn't know what they are doing...

<...Tennant said still not cooling below 76-77 F...>

In the UK, that temperature would be about right for a "good walk on a pleasant spring morning".

How far down does this tenant want to go?

This low maybe ....?

72-74F

I have ran into this problem with my dads AC system before. he likes it about 65 degrees if he can have it there.

One possible problem is the blower fan motor is is at too low a speed and not enough air can be pushed though the system. The blower filter may be plugged up. There may be lint or junk stuck all over the evaporator coils. I run into the dirty filter and coil problem with my dads system every year or so.

Does the outdoors unit sit in the direct sun and does it seem to be pumping out noticeable amounts of heat when its running?

Does the return line freeze up all of the way back to the outdoors unit?

If its freezing the return line all the way back to the compressor you are not moving enough air through evaporator.

If its not freezing the return line but is in fact dumping a good deal of heat out you may just have to small of unit. Most companies go by floor space of the home and don't factor in other variables that can make what calculated as being the right size in fact be too small.

If she has a lot of large windows with direct sunlight coming in the system has to work even more. Simply putting up better window shades and using them makes a big difference!

My dads house is roughly double the size of mine and he has a 24000 BTU capacity system and he can get his 65 degrees temperature when the system is working right.

My house is a old trailer with large windows. I am running a 24000 BTU window AC unit at one end and a 12000 BTU unit at the other. I still cant get below 75 most hot days but it far better than 85 degrees!

The central air that came with the house was a 24000 BTU rated unit and it was a joke. I use an independent watt meter for monitoring my AC power usage and just by going from the central air to the two big window air units I was able to get 10 degrees cooler in the house while still using half the electricity a month.

The fact that there seems to be some confusion regarding the proper charge in the unit could be a sign that something is restricting air flow(lack of ducts, dirty filter, dirty evap,etc), or it could be the service tech's inexperience. Hard to tell without corresponding pressures, temperatures, and amp draws. "Contaminated refrigerant" could be a gimmick to get you to pay for someone to remove old charge and put a new charge in of exact (correct) weight, since they seem to be lost regarding proper charge.

However, 2 tons is not a lot of refrigeration; how big is the house? How old? I would think a 2ton unit in central IL would be good for a house of about 800-900sq ft tops, unless it was super-insulated. My first house in St. louis (blt 1953, good roof insulation, no wall insulation) had 2.5T for 900 sq ft. If sized and operating correctly, your unit should be capable of at least a 20 deg delta T from outside temp.

Have you had anyone inspect the duct work? A loose or disconnected duct would overwork the unit and ultimately freeze up the evaporator.

make the Tennant close it's windows

In general being of an area with high percentage of humidity a lack of sufficient air flow will cause icing up and a reduced efficiency. But here may a few conditions to align your focus be.

Description from a Unico high pressure (pressure of air in ducting) AC system owner:

A main complaint is that the flexible plastic ductwork is not leakproof. With the high pressure, it only takes a tiny pinhole in the plastic to create a leak where you can feel the air blowing out. The way the flexible tubing fits together allows additional air to escape. I'm not sure if it is the inherent design of the system or if it was installed improperly, but the ductwork leaks at several of the joints. I am glad we didn't have the mini-ducts run in the walls between studs as the Unico ads show, since I have had enough trouble with the ductwork that having them inaccessible would have posed a major problem.

Another problem is moisture condensation on the outside of the ducts, especially where they run under the house. It gets very humid here in the summer, and despite the fibreglass insulation surrounding the ducts, they sweat to the point that you can actually see water dripping off. Another reason I am glad we don't have any ducts running inside the walls is that the condensation would have undoubtedly eventually caused water damage to the wooden framing structure of the house.

Just a week ago, the system stopped cooling. The units still ran, but there was very little pressure to the air coming out of the vents and the coolest we could get was about 85 degrees. I went under the house and discovered that the galvanised steel bands used to hold up the main central duct that feeds all the little ones, had rusted in two and the whole thing had dropped onto the ground, and the large rigid steel part had actually separated from the main flexible plastic section coming down from the blower unit. The reason the system was working so poorly was that most of the cool air was blowing out into the crawl space!! Instead of calling for service I repaired it myself, replacing all the original steel bands with plastic ones, using stainless steel screws to hold them up. (I suspect a commercial repair service would have replaced all the rusted out hardware with the same kind of rubbish that was used originally.) Fortunately I was able to repair the separated ductwork using heavy duty professional grade duct tape, the stuff that is actually designed to be used on HVAC systems.

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I have a Unico system installed by the prior owners in my circa 1970's colonial. It works rather well, the house cools mostly evenly (2 blowers, 1 in basement and 1 in attic) connected to 2 A/Cs outside. The blowers are not whisper-quiet, but I am used to old, in-the-window A/Cs that would wake you up at night. I think the amount of noise in a high velocity system is due to how well the installers did in snaking the vents. Also, I have taped some of the tubing in the basement where I have felt some air escaping. It's important to use that sticky foil tape, NOT duct tape, which will provide a better seal (not sure where I picked up that factoid).

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Ok...more background...

House size 1050 Sq ft ranch 7ft ceilings with 1 1/4 attached garage

r11 insulation in walls and r25 in ceiling

Duct work looks like new inside and out. No leaks in any of the supply tubes

Have not seen evap coil freeze up but did inspect it before the freeze up diagnosis and it is very clean

blower squirrel cage is clean

1 20X20 filter in the return air intake located in the ceiling in the main hallway in the center of the house (you can stand under the filter box and look into every room of the house..very open floor plan.

Air handler is suspended from the ceiling in garage with duct work going through garage wall into house attic.

garage is insulated with R13 walls and r25 ceiling

a 10,000 btu window unit in one of the bedrooms with a fan in the hall blowing down the hall would keep the whole house fairly cool except on those muggy 90plus days. (setup before the new unit)

windows are average size...nothing huge and are not in direct sunlight as the house is shaded from the southern exposure and house length runs north south.

The compressor is weak or system is under-sized, insulation inadequate or a combination.

Tenant can use UL approved window AC if they want to supplement the central AC system; on their nickle.

House should have R19 walls and R40 ceiling, this upgrade will pay-off in winter and the rental fee may reflect the cost of up grades.

is this the water chiller? Is the proper amount of antifreeze in the water? Too little and you have freezing issues at the plate exchanger, too much and you lower the capacity of the unit. If it is the water chilled unit, having too few ducts will obviously make it more noisy and not get off as much cooling but it isn't going to freeze up the coil, etc. Have you checked the water in and out temperatures? There should be sufficent difference in those two tempatures.

75 depending on the outside temp and humidy should be fairly comfortable. The unit is about the right size. a rule of thumb is (I think I remember) is a ton (12000 btu) per 600 square ft. This would seem to indicate that 2 ton for apr 1000 sq ft is about right. You can do all the heat loss or gain you want, but you only have so many size a/c units to pick from. 11/2,2,21/2,3 and so on. I would think that adding outlets (which is quite easy) would help. Also plant trees, they help. I have 2400 sq ft and a 3 ton keeps my house about 20 degrees below outside

Can someone say deja vu? I have the exact, and I mean exact problem. Wife and I bough a large old home (6000 sq ft) with 3 heating/cooling systems. We have a heat pump on one side of the house that works like a dream. The other side is hot water boiler which filled a room in the basement. Had it replace with buderus which also works like a dream. And then there is the dreaded Unico system. Again the lady we bought the house from was 85 and I'm sure never kept the house really cool. When we moved in we tried to turn the ac down to around 72 and it froze. Exactly what the other people said we had to keep it at 76 or above to not freeze. Now for the parade of hvac people who all said different things (6 to be exact including the installer of the system) None seemed to know exactly what was wrong. Just like the previous threads some took coolant out, others put it back, others said not enough outlets. Called Unico co and were absolutely no help. As I sit here sweltering in my office and once again trying to find someone in the area familiar enough with this system to make it work I'm also thinking about going to Sam's Club and buying a bunch of those roll around air conditioners and calling the unico a large brick in the attic. Any thoughts?

had this exact problem. unit was icing up quickly.

they cleaned the filters, made sure no blockages or restrictions, double checked there were enough inlet and outlet vents. Still icing.

they added more coolant, as high velocity systems are "supposed to have a little more coolant". no help.

brought in the Unico rep, and he spotted the problem rather quickly. something was miswired on one of the control cards. I am getting this info 2nd hand, so i am sorry i can not be more specific about what card and what problem it had. Fixed the wiring, and the problem went right away.

in hindsight, one other symptom...the unit was running all the time and not very efficiently cooling the house.

I would say that Unico was very good about supporting the issue.

unit has been working two full weeks in very hot/humid weather, and not a trace of freezeup.

If there is icing in your system it will be evident at the return line of the outside compressor in the form of ice around the fitting where the rubber insulation meets the unit.

If there is ice there then there is likely ice in the coils next to the blower in the house.

Very likely that fan is not turning on when it should . Or as long as it should.

This alone will cause the house to warm up as air cannot blow through the iced coils.

After it melts everything will seem fixed.

Even though it's not.

The only way this can be ironed out is with a service mechanic that knows what he is doing....which you don't seem to have...that only leaves you with one other option, replace the system with a conventional A/C unit that the mechanics available actually understand...

A high velocity air flow A/C shouldn't be any different than any other A/C unit, just has higher speed air ducting, so it's smaller, but the air is moving faster...Now 2 things come to mind after reading all this...the interior temperature is not reaching the thermostat setting, but the unit is cycling on and off...that shouldn't be the case...as long as the thermostat is calling for cooling the unit should be running...So 2 things point to an air flow problem, one is the noise, this means turbulence in the airflow, that there's a problem with the duct design....the system cycling while the thermostat is still calling for cooling means the unit is probably shutting off on low pressure, then resetting itself after a time....this again signals an airflow problem...

You need somebody to come out and test the amount of airflow you actually have instead of guessing....so you need a qualified service mechanic with a portable manometer, who actually knows how to measure the actual air flow....so for two tons of cooling you need a minimum of 800 cfm....

Measure the air coming and going, return and supply, and the temperature drop between the two....this will give you the actual BTU output of the unit, which should be the rated ~ 24,000 btu's for a 2 ton system...this will tell you if the system when running is working to spec....if this is the case, then reason for the unit shutting off while the thermostat is still calling for cooling needs to be diagnosed....if this is not the case, then the air flow needs to be corrected....

I can't tell you how many A/C service calls I've been to that have had several service mechanics already been there and been unable to correct the problem...A good mechanic is hard to find....so don't give up, there are still a few left....

Unit short-cycling can be caused by one of the outlet or supply ducts shooting air directly at the thermostat....the cold air hitting the thermostat causes the average air temperature reading to be incorrect, so you must reposition the airflow from that duct, or move the location of the thermostat, but the thermostat should be as close to the return air inlet as is possible...

1: Zombie thread, previous posting was 5 years ago, nobody cares any more.

2: what the heck did this ever have to do with ELECTRICAL engineering?

Regardless of what it has to do with electrical engineering the topic still has merit and adding to the thread is justifiable for those who are searching for answers to these problems.

Or so common sense would say.

More mechanical engineering than anything else...We do get a lot of the same problems year after year, nice to have a reference with a proper answer...

The high pressure AC sounds like what we call space pack around here unless I have that wrong.

Yeah what he means is high velocity air flow, which is for installation in places with limited space to run ductwork....

A bunch of 2" ducts, instead of one 8 or 10" duct....

I'm not a fan...

http://spacepak.com/

R-410 A is a Zeotropic blend and will fractionate significantly if you have leaks.This will radically affect cooling performance. If the charge is suspect for fractionation, you definitely do HAVE to replace it. Also, on such a critically charged system, the charge is generally calculated by weight, with Superheat being taken into account for the ideal charge on Fixed Restrictor systems. The only way to know what is in the system at any given time is to " Outweigh " the charge. This is TOO time consuming for the average parts changer.

The smaller the total system charge, the worse it will be. Putting residential systems together without leaks is a near lost art in this day and age. Most of what you get for Technicians are " Parts Changers " who have little respect for good workmanship. This can be especially true in remote areas, where one shop has a monopoly in the town. You are either at their mercy, or you have to import a Cracker Jack who is really savvy. A lot of the designs for this kind of gear have undergone yet another type of destructive generation from an Engineering standpoint. All of this reinvention of the wheel makes the units harder to service and diagnose, and harder to get correct parts for when they fail.

What has been done in the HVACR industry at large with all the gases developed since we had R-12,22 and 502 is all based on " Fradulent Pseudoscience " and underhanded politics. The entire industry is controlled by people who are confused and the gas development is getting worse. The trend towards using hydrocarbons will end in many disasters. Also running further up the periodic table and away from what worked the best is a colossal mistake. Everyone in the trade is under a great amount of mind control regarding the matter, and there is little sobriety left.

I never cared for R-410 A, but I have several machines on property that take the stuff. It is very unforgiving of leaks for sure. Often times, complaints about cooling perfromance can be very subjective. Having a very good record of readings from the original startup is helpful to any reputable mechanic who is installing systems. This includes gauge pressures, total system charge, temperature deltas, and so forth.