Why no air flow through home registers after running AC for a couple hours?

This season I switched on my air conditioning on my 19 year old furnace- A/C unit. After running for a couple hours I noticed the house was not getting cool and I didn't have any airflow coming from the registers. The furnace fan and outside AC unit were running but no air flow in the house.

I went to check the furnace and noticed I had left the furnace mounted Aprilaire humidifier on. I shut it off and closed the water valve. I then shut off the furnace. I thought maybe I had ice built up on the evaporator which might prevent the flow of air. After waiting four hours I restarted the AC and again had nice cool airflow through the house registers but after a couple hours running there's no airflow throught the registers.

I am baffled. This furnace A/C has worked well for 19 years and is serviced every couple years but not this year. It is a simple home builder grade furnace 80% efficient with single speed fan and single stage burner. The heat works fine.

What would cause this issue?

Furnace is made by:
Inter-City Product, Corporation USA
Fan Assisted Combustion Gas Furnace
Furnace Model series NUG505 or NUG507 (not sure). 80,000 BTU

AC mfg: Allegiance 10
Model 7A0030A100A0
mfg date 3/94

if the fan is running and no air, the coil is probably iced up.

This happens when you are low on refrigerant. (you have a leak)

The coil builds with ice and stops air flow.

I agree with Grumpy, even more so since you turned it off to let the ice thaw and it started blowing for a little bit... means it iced back up

One other thing,

whoever shows up is going to try to sell you an AC unit.

Be aware, you can still get freon 22. Wholesale price is about $15 a lb (probably $30.00 a lb to you)

410a Is considerably cheaper (about $4 a lb wholesale), but not when you take in the cost of replacing a whole system.

Interesting, the cause might be low freon level. I hadn't even considered that. Thanks for the help.

Finding and fixing the leak might present an opportunity to sell me a new ac unit. Some HVAC service people may say it is cheaper to replace than repair.

Is finding a freon leak easy? Are repairs reliable and long lasting.

If is not easy to find or repair, would replacing the 19 year old furnace and a/c make sense? I am not against replacement if the lifespan of the unit is 20 years. Is a 19 year old furnace at the end of its useful life?

I live in Chicago where it gets very cold and very hot.

Depending on where the leak is will depend on if you should repair or replace.... On a 19 year old unit, I would most likely get someone to come out and figure out the problem and ask for a quote for each. Finding a leak typically isn't to bad for someone who knows what they are doing and has the right tools.

Another reason a coil will ice up is low air flow. Check filter. If you can, look at the air inlet side of the cooling coil (indoor unit) and see if it is blinded by lint and 19 years of filter bypassing dirt. Usually a unit of this age (if the coils have never been cleaned) have a buildup on them.

IF you have a small leak, have it topped off.
I have this same problem and my son tops it off every season.
Last year, as a LAST ditch effort, I tried this...http://www.amazon.com/dp/B00559WTD2/?tag=atomicindus08-20....
We'll see what happens this season.

The avg lifespan is 15 years. Energystars website recommends replacement at 15 just for efficiency reasons. Yes leaks can be fixed, but by the time you spend all that money on repairs, how long before it needs more repairs. Yes r22 is still available but it is being phased out. The switch in cars ac r12 to r134 was in the early 90's, by 2000 r12 was gone. How long before r22 is gone? The switch was only 3 years ago and look at the price difference already. Say you fix the leak and 2-3 years from now it springs another leak. IMHO its time to invest in a new more efficient system with a 10 year parts and labor warranty. Just my opinion the choice is up to you.

dbonne said:

Another reason a coil will ice up is low air flow. Check filter. If you can, look at the air inlet side of the cooling coil (indoor unit) and see if it is blinded by lint and 19 years of filter bypassing dirt. Usually a unit of this age (if the coils have never been cleaned) have a buildup on them.

Click to expand...

+1.

To resolve, turn the furnace on... the AC coil will melt QUICKLY out the condensate pan

Thanks for the help everyone.

Low air flow is possible due to dust build-up on the AC coil. I've always thought this furnace didn't put out much air to begin with into the house. The furnace is cleaned every 2 - 3 years but I've never seen them clean the AC coil unit.

I change the filter every 2 - 3 months and have been for 13 years since I've owned this house, but still it could be low airflow after 19 years of dust and dirt.

I put a mirror into the inlet side of the furnace assembly near the fan motor (after making sure the furnace electrical was off) and couldn't see anything. I don't have an access panel below the AC coil but there is a small hole in the side of the furnace where the tech inserts a camera in past inspections but I believe this is for the heat exchanger. I don't have an inspection camera so I can't see the AC coil.

I will call the HVAC company who does my inspections and have him come out to troubleshoot it and also give me a quote on a new furnace and AC unit. I would rather fix this now when the weather in Chicago is mild then wait until winter or summer.

I'll let everyone know the result of the inspection. Thanks so much for sharing your knowledge with me.

Grumpy365 said:

One other thing,

whoever shows up is going to try to sell you an AC unit.

Be aware, you can still get freon 22. Wholesale price is about $15 a lb (probably $30.00 a lb to you)

410a Is considerably cheaper (about $4 a lb wholesale), but not when you take in the cost of replacing a whole system.

Click to expand...

Help me understand this. How is a "pound" of Freon measured? Do they weigh the cylinder before and after filling the AC? Or do they charge for each 1 psig of pressure added to the system. This has always baffled me how the tech measures the amount of Freon used.

I't weighed, just like potatoes.

welder4956 said:

Help me understand this. How is a "pound" of Freon measured? Do they weigh the cylinder before and after filling the AC? Or do they charge for each 1 psig of pressure added to the system. This has always baffled me how the tech measures the amount of Freon used.

Click to expand...

It is the weight of the refrigerant, we scale the cylinder before and after.

Replacing both furnace and air at the same time is a good idea, even if you stay with a 80% furnace you can add features that will improve comfort and lower operating cost such as 2 stage heating and ECM motors.

R-22 is still available and will be in the future but its cost is yet to be determined. We will only install an R-22 unit as a replacement if the indoor coil is newer and we can come up with an AHRI match for the coil/condenser unit.

Every furnace manufacturer has multiple lines of equipment, make sure you know what you are being quoted so you don't pay top of the line prices for builder grade equipment.

A proper install is key to HVAC equipment leading a long, healthy and efficient life.

I had a problem with my 30+ year old furnace last year, and the repairman told me that 80% furnaces would not be available after the end of last year. His cost for a new furnace and a/c was almost 5k. I'm still running the old furnace a/c. I'm not sure I like all the wizardry of the new high-tech furnaces.

ford33 said:

Thanks for the help everyone.

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I will call the HVAC company who does my inspections and have him come out to troubleshoot it and also give me a quote on a new furnace and AC unit. I would rather fix this now when the weather in Chicago is mild then wait until winter or summer.

I'll let everyone know the result of the inspection. Thanks so much for sharing your knowledge with me.

Click to expand...

Well, what was the deal???

We decided to replace the 19 year old equipment with new equipment.

I called three HVAC companies and had quotes that were all very similar. I wrote a request for proposal to keep make sure everyone had the same information and had them quote the furnance, air conditioner, filter and installation. I let them size the equipment and make suggestions for improving the installation. I specifically asked for an 80% effeciency furnace and 13 Seer AC unit. I did improve the air filter from a 1 inch thick filter to a 5 inch filter. It was the filter that caused problems today.

Everyone tried to upsell me to a 90 - 95 % efficiency furnace and 14+ seer AC unit. I declined as the return on the investment for greater efficiency is almost as long as the life of the furnace 15 - 19 years. I live in a town home that is 19 years old and is well insulated and our heating and cooling needs are modest.

They were going to install the system today but...

Truck shows up at 7:30 this morning and we go over the work plan and equipment list and discover they have the wrong air filter element, wrong air filter housing and also cannot mount the furnance on top of the filter because they don't have the ablity to fabricate a supporting stand/box in the field. The door to the furnace room is only 24 inches wide. This prevents mounting the wide filter next to the furnace as it would be impossible to change the filter or properly service the furnace.

They made some drawings, took some pictures and measurements and went back to the office telling me the sales guy never said anything about mounting the filter under the furance. It was clearly stated in the proposal and again in an email that I sent to the sales person confirming the work to be done. They will reschedule later this week.

I am disappointed that communications is poor between sales and installation. This is fundamental to any service business and yet it isn't done well. I'll give them one more chance to get it right. If not done by this week, I'll move to the next HVAC company. I haven't paid for anything yet.

Being from the Chicago area, out of curiosity, what is the company that you chose and how much will it cost you?

Here's an update on the installation.

Integrity Heating and Cooling installed the new furnace, AC and air filter along with new copper tubing for the AC yesterday without issues. Due to the large air filter and limited width of the furnace room door they mounted the filter horizontally beneath the furnace. This required fabrication of a short piece of ducting and a metal box to support the furnace and filter. It was a nine hour job by two guys to get everything installed.

I am happy with the work. AC is working fine today. The total cost was $4021.

Thanks to all for helping diagnose the problem and suggesting fixes.