Home central A/C evaporator frozen?

Yesterday, the breaker tripped on my blower motor at home and my housesitter reset the breaker and left the unit running. Today, there's very little air coming out of the vents which leads me to believe that the evaporator coils are frozen and restricting airflow. The plan so far is to run the heat for about 30 mins to thaw the coils then let it sit for 2 hours before turning the A/C back on.

First question... Does my diagnosis sound right? I've done some research online and the compressor running without the fan is a typical cause of the coils freezing which is a popular cause of low air flow.

Second question... Is my resolution going to cause more damage than I may already have? I've read that with a heat pump, that running the heat can speed up the thaw but I have forced hot air but assume that once the air handler gets hot, it will thaw the evap coils pretty quickly.

Any help is appreciated.

Re: Home central A/C evaporator frozen?

So, I talked to the housesitter and after running the heat for about 30 minutes then letting just the fan run for about an hour the flow with just the fan on is about the same as before the heat was run BUT the flow was supposedly better with the heat on which, if I understand how this thing works, doesn't make sense.

Gonna give it another hour then turn it back on and hope for the best.... Ugh...

Re: Home central A/C evaporator frozen?

on a fosil fuel furnace the fan motor runs slower in heat mode ,fan in the on position is high speed as well as in cooling mode also check the air filter

Re: Home central A/C evaporator frozen?

You don't need the heat. Just run the fan without the compressor until airflow is normal, plus an hour or so. Turn the compressor on and let her run for a while. If she ices up again, shut down and call your friendly neighborhood HVAC dude.

You will probably need a couple pounds of refrigerant to make it good again.

Re: Home central A/C evaporator frozen?

How long has the system been in.
Most common cause is lack of air flow... check the filter first .. make sure the squirrel cage fan set screw is still tight and not letting the shaft spin ... if those two are o.k. then the surface of the coil could be dirty... or a leak, which would require a leak search and repair before adding refrigerant.

Re: Home central A/C evaporator frozen?

How is the filter? Is the coil clean? Units freeze differently believe it or not...Low air flow freezing makes the ice look powdery like snow, freezing from a refrigerant problem looks solid and shinny like an ice cube...My guess is you have a unit with a charge problem(Overcharge can cause the unit to freeze also)...Or a fan motor or capacitor that's on its way out...If you have a cap tester, and amp clamp and a surface thermometer and a set of gauges I can help you, otherwise I would just call someone...

Re: Home central A/C evaporator frozen?

The entire unit is over 30 years old and it was just serviced last year when seemingly the same thing happened. I called the HVAC guy who couldn't find anything wrong with the unit but cleaned the coils and gave her a tune-up. He said everything looked good. I haven't been home yet, but the unit has been off for more than 12 hours with the fan running and the house-sitter is going to turn it back on this morning and see if it can keep up with the day.

I know that the initial cause of the problem is the breaker on the fan control getting tripped so I'm hopeful that after 12+ hours of the compressor not running that it'll be thawed and ready to run today.

Re: Home central A/C evaporator frozen?

Something sounds kinda fishy...Breakers don't usually trip for no reason...It is possible though that the fan would have its own breaker and the control voltage could come from the outdoor unit and keep the compressor running with no airflow and freeze up the unit...I would put a low pressure switch and use a contact on a relay for when the fan is energized to tell the compressor its ok to start(a fan proving switch basically)...when a unit freezes it breaks down the oil and screws up bearings and internal parts of the system, leading to compressor failures and other issues...

Now a days a service guy giving the unit a clean bill of health doesn't mean anything...80% of the guys I know in the trade are in the wrong line of work...

Re: Home central A/C evaporator frozen?

How well was the system running before the breaker tripped? Is this a split system or a packaged unit? If it is a split system I will have to agree with hrdwrkingacguy that the air handler fan motor is on a separate circuit and not supplying the control voltage. It is possible that this circuit is shared with something else in the house (should not be) or the fan or cap is on it's way out.

Re: Home central A/C evaporator frozen?

It turns out that it wasn't the breaker for the fan control that tripped, but the relay that activates the fan fell out. This happened before but the result is that the fan wouldn't come on. When the button on the fan control was pushed, it put the fan in MANUAL mode which is why the fan was running afterwards. I had thought it was a breaker but apparently it switches from AUTO to MANUAL for the fan.

So, the fan is working and I know why it stopped and the unit is thawed but the outside unit still isn't working. It tripped the 50A breaker each time it tried to start so I replaced the breaker thinking that it may be defective (it's very old) and now the unit comes on at a very slow speed. In fact, it almost seems like the fan only is coming on and not the compressor itself but I'm not sure if they're on the same motor or not.

I have someone coming out this morning to take a look at it since I've done everything in my skillset. I could open the unit and check out the electrical aspect of it, but he's already on his way so...


Thanks for all of the help.

Re: Home central A/C evaporator frozen?

If the compressor on top feels hot, take the wires off the terminals of the compressor and ohm from terminal to termial if R to S has resistance but C to R and C to S doesn't you have an open internal protection and need to cool off the compressor...Probably not going to get that lucky though...I think you have something grounded and the outdoor motor is seeing 115v instead of 230v...Does it literally seem like the motor is running really slowly like 1/2 speed? grounded compressor with a open IP with a blown fuse will do that...

Re: Home central A/C evaporator frozen?

Might be a bad capacitor on the compressor. could be a contactor one legging it also.

If it's thirty years old he will probably tell you to replace the system.

Let us know what they say.

Re: Home central A/C evaporator frozen?

tswiczko said:

Might be a bad capacitor on the compressor.

Click to expand...

I would agree. Just had the same thing happen to a friend of ours. Changed the capacitor for them and back to normal.

Re: Home central A/C evaporator frozen?

I'm having the hardest time getting someone to come out and look at this thing...

I did find yesterday that half of the contactor was burned so I replaced it and am still tripping the breaker immediately which should mean a dead short somewhere. If I remove the lead from the contactor that goes to the compressor, the fan runs full speed but obviously the compressor doesn't. Sounds to me like a bad compressor but I'll find out for sure hopefully today. I've got a service call into the utility company that says someone will be here between 8a and 1p. They've got 1.5hrs to get here. UGH!

Re: Home central A/C evaporator frozen?

So here's the latest... The guy showed up almost 3 hours late and took 20 minutes to put the DVM on one of the wires feeding the compressor then told me it's a dead short which explains the breaker tripping. So, I need a new compressor but since the unit is so old, it looks to be more economical to change the entire outside unit since parts for a 30yr old condenser will be hard to find.

I'm planning to move within the next 12 months and don't want to spend a fortune (6-8k is the guestimate I was given) on replacing the inside and outside units to switch to the new refrigerant so my new question is what would be involved in replacing the outside unit with another r22 unit, either a new or gently used one. I know that either way, they will need to be charged with refrigerant but I've heard from some that the evap coil would still need to be replaced but the guy that was out yesterday made it sound like I could get away with just the outside unit. Also, what I have now is a 3T unit but I've seen some year old 5T units and am wondering if moving to a 5T unit would cause more problems than sticking with a 3T.

Thanks again for all of the help and advice.

Re: Home central A/C evaporator frozen?

The indoor coil is matched to the outdoor unit( sometime a coil of about a half ton larger is used for more dehumidification 3.5t coil with a 3t metering device) for 3 ton coil 3ton out door unit also air flow over the coil is not a perfect match but close 400cfm per ton 3 ton= 1200 cfm. most standard blowers on residential units are 2-3 ton or if oversized 3-4 ton. Duct work will also need to be sufficient to handle the increased air flow. if not sufficient then another upgrade will be needed there. you would need to find out which blower size you have, change the indoor coil from a 3 to a 5 ton then the out door unit to 5 ton provided the line set was of sufficient capacity and electrical was sufficient(usually the electric is sized to the unit requirements a 5 ton will draw more amps than a 3ton)

Oversizing the A/C system will cool too quickly and not dehumidify properly and could cause air quality issues in the structure(mold growth)

if you stay at 3 ton, recover the r-22, cut the old unit loose, hook the new unit up, be sure to install a suction line filter drier as well as a liquid line filter drier, evacuate and verify there are no leaks and recharge.

be sure to get a sticker of recovery from the tech you get to do the work some scrap yards won't take refrigeration equipment unless they have proper recovery sticker on them.

good luck TB
ps. if you are looking at a 1 year old condensing unit it is probably r-410 and not 22

Re: Home central A/C evaporator frozen?

Ok, so stick with 3T so I don't have to replace everything. Sounds like a plan to me. The 1yr old unit, from what I understand, was put in to replace an older unit (r22) but was later upgraded because an addition was put on the house and they needed to upgrade to a larger unit so they went to the newer refrigerant. I know that I can get brand new r22 units but they're "dry" units that need to be charged. Is it possible to recover the r22 that's in the current system and using that to charge the new unit if I end up with a "dry" unit?

Re: Home central A/C evaporator frozen?

If you do it will probably need to be recycled through a filtering unit before it is re-introduced to the system. Since you are moving it MIGHT be OK for a year. but I would put new in myself.just for the simple fact of keeping the system as clean as possible. you're old system has had a burnout and could have a high level of corrosive components in the refrigerant and oil still in the refrigerant.

that's why you put a suction as well as a liquid drier to remove the contaminants left in the line-set and indoor coil. using old refrigerant and oil that hasn't been run through a recycling filter system is defeating the purpose of repairing the system.. I have seen this type of action burn out new compressors in a matter of days by eating the insulating varnish of the winding's.. in fact they make a flush (RX-11) for for this sort of situation but I feel it may be overkill(last time i used a flush it cost almost 300 dollars for the flush itself)

you would be better off using virgin refrigerant.

if the unit you are receiving is used and was pumped down into the condenser you should have enough in that unit for the system with a need for a few ounces to set superheat if it needs anything at all.

If you get a dry unit I would definitely use virgin refrigerant. to prevent voiding any warranty you might get on the unit

Re: Home central A/C evaporator frozen?

It looks like about $2000 for a dry unit plus the install so this is probably the way I'll go. I have a couple other people I want to talk to first, but that seems about as good as it's gonna get without going with a used unit. That price includes new refrigerant and a 2yr labor / 5yr parts warranty. Should definitely last longer than I intend to be there.

Re: Home central A/C evaporator frozen?

You said he put his meter on a wire feeding the compressor and it read shorted??? Did he take the terminal cover off the compressor and make sure nothing just fell off or a wire melted??? If it were me I would just replace the compressor if you are planning on being there for a year...Pull the refrigerant charge, replace the liquid drier(You don't need a suction drier) put in some acid away and evacuate and recharge...On the electrical end I would replace the contactor and the run cap and add a 5-2-1 start kit...That job costs 650$ to do yourself if you have access to parts and the tools...<2k if you don't...

A service tech is always going to suggest the easiest/most profitable job...There is no reason you can't just replace the compressor...

TBarCYa said:

It looks like about $2000 for a dry unit plus the install so this is probably the way I'll go. I have a couple other people I want to talk to first, but that seems about as good as it's gonna get without going with a used unit. That price includes new refrigerant and a 2yr labor / 5yr parts warranty. Should definitely last longer than I intend to be there.

Click to expand...

If this condenser was built after jan 2009 it won't work...You can get away with an oversized 13 seer indoor coil on a strait cool unit, but a 13 seer condenser on a smaller < 10seer indoor coil is asking for problems...

You would need to add a suction accumulator, and the smart thing to do would be to install a liquid line solenoid and wire it for a one time pump down, also you need a fan cycling control to maintain head pressure...I had to do that two weeks ago because a customer wanted to just replace his old condenser...The unit is totally screwed and never going to work...Mismatching is a bad idea...