Air Conditioner Freezing Up

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The fan motor on my outside unit died last week. I took the fan motor to a local appliance parts store and they gave me a new one. The new one had a longer shaft but they said that did not matter. I replaced the fan motor and it seems to work fine. The air is blowing up out of the unit. However, when I run the air now the interior unit freezes up.
Any suggestions would be appreciated!!
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The two common causes of the inside unit of an airconditioner freezing up is low refrigerant in the system and low air flow across the coil of the inside unit.
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Michael. wrote:

Assuming the replacement fan is the correct rotation and RPM, the other possible causes of evaporator freezing are that the system is low on refrigerant or there is an airflow blockage (obstruction in the air ducts, dirty air filter, or dirty evaporator coil).
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Travis Jordan wrote:

Did you reinstall the condenser fan EXACTLY where it was when you replaced the fan motor? On many systems the placement of the fan blade within the shroud can have a big effect on airflow.
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Unfortunately I already discarded the old motor. I have tried raising and lowering the fan blades. I tried moving the blades up to the top of the unit as far as it will go. I have also tried moving it down about 4 inches, and 2 different spots in between.
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Michael. wrote:

I'm no technician, but I don't see how the fan to cool the condenser unit could have any affect on icing up the evaporator unit. Others pointed out the potential problems. So, the cause is either unrelated to the condenser fan or you might have caused a loss of coolant when you changed the fan motor.
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1- Did you replace the motor with the EXACT same HP and RPM? If you did not, you have a problem. 2-did you put the fan back EXACTLY where it was located in relation to height? if not, you have a problem.
If you have too much airflow over the condensor now, you have changed the operational characteristics of the unit, and while you can correct it with the proper tools and knowhow, I would suggest that either you had an issue in addition to the fan motor, or, you have put a fan motor on that is too high of an RPM now, and thus, created a charge issue with the unit.

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CBHVAC wrote:

Are you talking about a home unit? If so, I don't believe it. My condenser unit couldn't blow any harder. If it doesn't blow enough, that is obviously a problem. Besides the OP indicated the motor only differs by having a longer shaft.
Blowing too much, if possible, would have less effect than the normal changes in outside temperature. How in the hell could any hp change or motor speed adversely affect the condenser as long as it is keeping the coils cooled? Unless, of course, some one has some cobbled up design that involves electronic control of the blower motor that is supposed to save energy.
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George E. Cawthon wrote:

Excessive condenser airflow will simulate a lower ambient. If ambient is in the mid to low 70's as the OP states, then with a larger and thus slightly faster motor the unit will *percieve* an ambient in the mid to upper 60's, in which case a piston evap coil can easily freeze up, especially if it was a bit undercharged to begin with. The new motor can very well be the difference between evap freezing vs not freezing. This can also occur even if the motor specs are identical. How? Well let's get this out of the way too. If the old motor wasn't running up to speed and the refrigerant charge was adjusted under those conditions, then it will have actually been left undercharged. The result is the same as installing a higher HP motor.
In this case the OP said that he also cleaned the condenser coil. This could very be the only thing that caused the evap to start freezing up.
hvacrmedic
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RP wrote:

I'm astounded. If what you say is true, then some engineer should come forward with a new design or at least a new control system that would put all the others out of business. Further, homeowners would be constantly experience problems for which there was no remedy because they would be due to environmental changes. And the units on autos would be virtually useless.
I think you are reaching. If the charge is wrong it is wrong. Sure it may not show up under some conditions and new changes could make it show up, but the problem is the charge.
My home unit works in all kinds of weather and all reasonable temperature and humidities and I have never experienced any kind of freezing up (of course I don't run it when the temperature is 20 degrees, in fact, it never run when the ambient temperature is below 75 degrees.)
My automobile units work in more drastic conditions since my truck AC works in any temperature at some setting and it never fails to cool.
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George E. Cawthon wrote:

This is Turtle.
George , Richard put the correct words in his writting as the system could be slightly under charged in most all his cases which left the door open to cause of low on freon to freeze it up. Richard covered his ass with correct writting but the one you should be talking to is CBHVAC for he is the one that put his foot in his mouth here by fully stating the a fast running condenser fan motor will freeze up a evaperator coil, period.
TURTLE
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TURTLE wrote:

As much as you'd like that to be true Turtle, I didn't get that out of what Steve said.
hvacrmedic
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RP wrote:

This is Turtle.
DUUUUUAAAA! I can tell the diffence of who is writting on the post by the names above them. You need to go back and read the last line and the O.P. was having a problem of the evaperator freezing up and CB was giving causes. He better get Paul to delete that post for CB to get him out of it.
What you read and what i read must be two different thing. Richard you do need to talk for him here for it's not a matter for him to talk about.
TURTLE
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George E. Cawthon wrote:

Hey speedy, I didn't say there was a problem with the motor, did I? This was just a description of how the unit could have gone from not freezing up to freezing up by changing the motor and/or cleaning the condenser coil.
The only real problems are that, no.1 he's running the unit when he should have the windows cracked. Truth be known, and this is no.2, he probably either needs a new air filter or the evaporator coil is plastered with years of his own filth from not changing the filter regularly. Adding refrigerant may indeed be the only fix required, no.3, but this isn't what you asked about numbnuts. You specifically asked how increasing condenser airflow could lead to a freeze-up condition. If you don't understand your own narrative then you should think about forgoing the reading of anyone else's.
hvacrmedic
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RP wrote:

I agree with most of your statement Slick. But I didn't really ask a question about how it could freeze up, I indicated incredulity at your statement about the "perceived" lower ambient temperature. And, I pointed out that it would really be a problem with the coolant and not the blower.
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George E. Cawthon wrote:

This is Turtle
George you will never be answered by anybody about your statements above because it is a cover up of someone bullshitting and got cought doing so. CB said it and Richard covering it up. this is the end of it for being caught bullshitting you have to forget about it and move on.
TURTLE
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CBHVAC wrote:

this is Turtle.
the last line you wrote above here about a problem such as the op that the unit will freeze up with the condender fan blowing too much air. In 40 something years in the HVAC/R business have i ever heard of moving too much air across a condenser coil will freeze up the evaperator coil if it is properly charged.
Now you need to rethink what you stated it here about a faster condenser fan motor speed will freezer the evaperator coil up with a properly freon charge of the system.
TURTLE
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TURTLE wrote:

That only proves that over that 40 years you weren't paying attention. Do you recall the reply that I made to you about retrofitting a 13 SEER condenser to a 10 SEER air handler and evaporator coil? You can add refrigerant in order to get the suction pressure back up, and the superheat to where it is supposed to be, but just changing a motor out never added a drop of 22 to a system did it? Even if you go back and fix the homeowner's fuck-up by adding 22, the suction pressure will still run a bit lower than before at the same superheat because the subcool will run much higher than before.
hvacrmedic
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RP wrote:

This ios Turtle.
i never said to CB anything as to the effect of the system not running right but ONLY that a properly charged system and to put a big ass fan on the condender will not cause the evaperator to freeze up . All that your speaking about here is freon related problems and not fan speed problem with nothing else in the picture. Your bring in freon charge being off or not right to cause a problem when speeding up the fan but you have to have a freon problem and not just a fan problem.
All that you spoke to me about was a freon level being off or different and needed to be changhed.
So if you have a properly charged hvac syustem moving more air throught the condenser coil will NEVER cause the evaperator to freeze up. you was right in your words but CB was wrong big time. Go back and read what CB wrote and see.
TURTLE
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TURTLE wrote:

Every word of CB's post was spot on. You can never adjust the charge correctly on this system after the condenser airflow has been increased over its engineered value, unless you make a few other modifications. One of those is the piston size, just in case you don't remember that post that I spoke to you about. With the old piston and higher condenser airflow the system is mismatched. The subcool will run too high and the superheat will never correspond to the superheat chart over the range of ambient temps that the unit runs under. Moreover the system will be easier to freeze up, i.e. it will do so at a higher ambient than it did before. Even when you change the piston out, the indoor air volume will now be a tad too low since by increasing the condenser airflow the capacity of the unit will be a tad greater than before. Now don't get me wrong, the system will work, but it will never work as it was engineered to work. Put a TXV on the evap coil and you have yourself a blanket fix to all of these potential problems.
Now there's the issue of the under-loaded condenser fan motor and premature failure due to overheating. This can be fixed by selective capacitor sizing as a hack fix, but it isn't supported by the motor manufactures unless you have the trip-saver, but I'm not even going to go into any of this with you since you already have enough to digest for one night :)
hvacrmedic
hvacrmedic
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