Need HVAC long-distance hands-off diagnosis!

I bought this house mid-April. When the inspector came out, he noted the A/C was not working (coming on but then immediately shutting off seconds later). The A/C had to be fixed by the seller as a condition of the sale. They did some stuff (I can’t read the scrawl on the ticket but I was told the major problem was it was needing freon, which was replaced) and it supposedly fixed the problem.

The A/C worked fine when we took possession; but then, it was still only April so most days it wasn’t even on. May came and it worked fine, but of course, it still wasn’t hot, just warm, upper 80s to low 90s stuff. Then we had a mini-heat wave in which temps hit 100° three days in a row, and my A/C never cycled and still it got no cooler than 77° in the house, with a mid-day high of 81°.

The seller bought a homeowners warranty (again as a condition of the sale) so I called them, they contacted their A/C company and the guy came out. He said it needed a pound of freon. I expressed surprise and mild doubt and showed him the ticket from the month earlier. He said that he couldn’t do a leak test on a first visit, but if there were still problems, to call the warranty company again, and at that time they would probably authorize it.

He left the thermostat on 75° when he left. All the rest of the day it stayed at 75°, and although I didn’t really pay attention, I also did not become aware that the A/C was not cycling (a vent blows on my left hand whilee I am at my desk, so after a while I notice it usually).

So, no problem. Or so I though. The next day the same thing - no lower than 77°, even though I hadn’t touched the thermostat since he left.

Five days later he comes back, did some extensive crawling around and says “when this unit was moved, they used two 9” intakes instead of one 12". I called my supplier and he said 9" is not enough, you need 12", so we’re going to have to put in a new intake duct for $700.00." I told him I’d think about it and get back to him.

I have several reasons to doubt this theory of his. First of all, he didn’t say the entire dimensions of the 9" ducts, but unless they are narrower than 8" (which I realize is entirely possible) then the two 9" ducts would provide MORE air return. Secondly, this house is almost 25 years old and has had two previous owners, and I have a very, very hard time believing both those families enjoyed living in a 81° house with the added luxury of electric bills that must have exceeded $300.00. But, most importantly - THIS UNIT HAS NEVER BEEN MOVED. It was replaced 11 years ago, but I looked at this same floor plan at least 3 times in my househunt, and they ALL had the air handler in the attic, just as mine is. For that matter, all the houses in this neighborhood that I looked at, as well as another addition built by the same builder, had the units in the attic. These are small duplexes and I am certain they were designed that way to allow for more usable floor space. So, the unit (and every other unit in this floor plan) was INSTALLED with the 9" ducts.

However, to complicate my decision-making process, I have one very good reason to believe his theory: it is obviously an intake problem because the refrigerated air was measuring 43°! And, in fact, I myself was beginning to wonder if it was an intake problem because, despite the fact that I own five cats, the filter still did not need replacing after a month.

Do I need to call my warranty company and insist they send out a technician from a different company, or do I need to fish out my credit card before it REALLY gets hot and get the 12" duct? If this theory sounds wonky, what other possibility could it be?

I got laid off shortly after moving in, so right now money is tight, or I’d just hire my own A/C company to get a third opinion. Or just go ahead and get the duct but put it on my card so if that didn’t solve the problem I cuold dispute it through my credit card company. But since living expenses may well be put on credit cards by the end of summer if I haven’t found a job, I don’t want to put what may be unnecessary “repairs” against my limit.

Thanks in advance.

No HVACs techs in doperland?

Coming on but immediately shutting off can be a few things. If the compressor is bad, it will try to start, but the thermal protector will cut it out within a few seconds. Another is a low suction pressure cutout, which would coincide with a diagnosis of being low on refrigerant. Upon compressor startup, if the suction pressure drops below the switch setting, the compressor then stops-this sounds like what you were experiencing.

If I’ve got to add a pound of R22 to a system, I darn well want to know, and the EPA tells me to figure out where it went. Dumping a pound into a system and walking away isn’t how a technician should address the problem. Someone who “can’t perform a leak test” shouldn’t be working on HVACR equipment, IMHO.

The “moved unit” explanation sounds goofy to me. Once an air handler and evaporator are installed during original construction, nobody moves diddly, unless there’s an addition and you’re bumping up the tonnage of the condenser/evaporator pairing.

I’d try a different technician, because I can’t say for sure the next time I’ll be in your neighborhood. :wink:

lorinada,
First, this isn’t terribly “long-distance”, since I live in Arlington (Howdy, neighbor!).

My qualifications: 6 years as HVAC tech with my own company, 6 years chief engineer for commercial properties, 9 years as an HVAC controls contractor and a BS in Mechanical Engineering.

From your descriptions (which are MUCH better than anything I got as a tech - “It doesn’t get cold, even when I turn it all the way down.”), I’m going to guess that you have a dirty evaporator coil and possibly a Freon[sup]TM[/sup] leak as well.

All of the symptoms you described would be consistent with insufficient air movement. It will lower the system pressures and look like low freon to a tech. It will cause very low coil discharge temperatures, and it will appear to have a low return air flow.

The bad part of this is it will cause liquid freon to flood the compressor which washes the oil away from critical moving parts and puts considerable stress on the valves in the compressor (I’m assuming you have an older reciprocating type hermetic compressor).

Here’s how to check it out. The evaporator coil is the part of your furnace with freon lines attached to it. There is a small copper one and a larger, insulated one. It may be separate from the furnace itself or built-in. You will need to find a way to get a look at the inlet side of the coil. In some cases this means removing the blower fan, in others, cutting a hole in the plenum. (Remove all power from the unit, wear gloves and safety glasses, use adequate lighting, drink plenty of fluids, etc. Do not attempt unless you are somewhat mechanically savvy).

To clean the coil properly, you would need to recover all the freon in the system, remove the coil and clean it with strong detergent, brush, and a high pressure sprayer (don’t flatten out the fins). However, if you can gain access, it is possible to improve the condition greatly with a can of evaporator coil cleaner and a nylon brush (available at most hardware stores).

This really should be done by a professional, but if you can tell them the problem, you will save them time and you money. If my diagnosis is correct, your home warranty company may refuse to cover it as a “previously existing condition”. A reputable HVAC company will charge about $250 -$300 for this service.

Also, (I almost forgot) if the evaporator coil is very dirty, chances are that your blower fan is also caked with gunk and will need to be removed and cleaned.

Finally, even if everything I’ve guessed is correct, it still may not fix all the problems. Once you get enough air over the evaporator coil, it could put enough of a load on the compressor to push it over the edge. Sometimes fixing the obvious problems just uncovers the rest of them.

Good Luck!

You can also check to make sure that the ducts are free of obstructions, that there are no closed dampers, etc. If there is an obstruction, it could be on either the return side or the supply side. I wouldn’t automatically decide that the return duct was too small until I checked out the entire duct system.

Also, is the duct rigid metal duct of flexible duct? Unfortunately, a lot of residential installations use the flex duct, which performs poorly when new and may be close to failure at 25 years. You don’t want it, and if you do need new duct, for $700 you should be getting rigid duct with insulation (on the outside of the duct).