Older A/C system fine when new, but years later freezing over daily (Rheem RAKA-037JAZ)

[grasshopper #309287721]

Good Evening!

 

We have a Rheem whole house air conditioner freezing over.  Even with a new, low-restriction (FPR 4) filter in place.  Even with no filter in place.  Even with the evaporator coil cleaned off.  Even with the condensor coil cleaned off.  Even with all the registers wide open.  Even with the thermostat set to cool to 73 degrees (the freezing over happens at both temps well above the set point as well as at the set point).  Even with the blower on all day / all night (to keep the air temp in the house uniform).

 

We live in a dry climate and do not have an outdoor humidity problem.  But we can induce A/C freeze over within an hour just by having several household members do their showers in close proximity time-wise.  But even without anyone showering, the system will freeze over every day that it is running.  It will also freeze over sooner on a hot day if it rains and the temperature drops 15 or so degrees.

 

We never noticed the system freezing over the first 3-4 years we had it.  If it was freezing over, it must not have been completely freezing over since the house still stayed cool.

 

I've had 4 different residential HVAC businesses come out and look at this freezing over problem.  Actually, 5 businesses counting my neighbor at the time who did residential HVAC but has since moved out of state.  He was actually the most helpful, but I've still got the problem.

 

I've tried everything I can think of to keep this thing from freezing over (changing filter monthly, cleaning condensor and evaporator coils, adding return air vents, having techs come out and add or subtract Freon according to their recommendations, keeping the register wide open).

 

Something I haven't done yet is replace the 1/2 HP blower motor with a 3/4 HP blower motor (that was one of my neighbor's suggestions).  That's a more expensive option and I'm not even sure if it can be done without changing out the furnace as well.  But I am considering it.

 

Also, an acquaintance in the HVAC business (not my neighbor) asked me if the system had a TXV thermal expansion valve.  I didn't know (and still don't know).  He said if it didn't have one, putting one in would keep the system from freezing over.

 

I did get quotes for doing that.  They both came in at costs on par or higher than what we paid to add the A/C system to the house in the first place.  I guess that's inflation.

 

Another option that occurred to me was another supply-side restriction (the first supply side restriction being at the evaporator coil - dog hair).  Even with all the registers wide-open, we still eventually get freeze over.  Maybe there's something blocking the supply side between the evaporator coil and the registers?  But we've had the ducts cleaned.  Maybe the duct cleaner missed something?  Is there a way (without spending $1000) I can get a camera through the ductwork to check for restrictions?

 

Another person suggested that the thermostat should periodically (and automatically) cycle the compressor off before freeze over.  Even if the temp at the thermostat is still several degrees above the temp the system is trying to cool the house down to.  I hadn't heard that anywhere else and so I don't know if I should try another thermostat.  The one I have (not the original) is a Lux TX1500b.  I have it programmed to use a set point that is 90 degrees F twice a day for 30 minutes so the evaporator coil will defrost (it has 4 temp settings per day).  It is set to 73 degrees F the rest of the time.

 

Here's the hardware info:

 

Model No: RAKA-037JAZ

Manufactured: 03/1998

Installed: 1998 (or 1999 - working from memory)

 

The air conditioner did not come with the house - we had it put in 2-3 years later.

 

The evaporator coil is installed on the supply side of the furnace which is about 2-3 years older.

 

Furnace is a Carrier:

 

Model #: 58PAV111-16

Product #: 58PAV111-16116

Blower: 1/2 HP

Manufactured: 1996

Installed: 1996

 

If you read this far then I owe you a beer. 

[smee123]

I'm new to this field but... its hard to clean the evap coil properly.

Has anyone done this?

Aside from brushing off dog hair.

 

 

[grasshopper #309287721]

It was hard to clean the evaporator coil.  But my former neighbor (the one in the HVAC business) cut an access hole on the supply side of the duct work and also cut where needed into the triangle-shaped sheet metal panel that connected the two halves of the evaporator coil array (I don't know what the industry term is for those two sections of the evaporator coil that sit at roughly a 90 degree angle to each other) so that we could get light and a hand in there.

 

The dog hair was actually matted across the surface of the array along with what I can only imagine was a combination of dust and dirt.  It was a thin, dense, impenetrable mess.  He picked it all off in pieces with his fingers.

 

Airflow was improved after that, and it seemed to delay the freezing over, but we still get freeze over.

 

Are there other ways to clean the evaporator coil besides picking at it by hand?  Maybe there's other foreign matter between the fins that we can't see.

[m_west5]

What are the low and high side system pressures? Check the paperwork from the 4-5 companies who looked at it. Hopefully one of them put their gauges on it.

Did they check the blower motor fan rpm was correct?

[grasshopper #309287721]

What are the low and high side system pressures? Check the paperwork from the 4-5 companies who looked at it. Hopefully one of them put their gauges on it.

 

I think I may have that information from at least one of the companies.  But I will have to dig it up.

 

Does it matter what the outdoor temperature was when they took the readings?

 

Did they check the blower motor fan rpm was correct?

 

Nope.  Even my neighbor didn't check it the actual speed of the blower motor.  He did check that the furnace logic board (I don't know the industry term for that one either) supported 2 speeds for the blower.  Something about it always needing to use the higher speed for the A/C.  And I think that somehow he confirmed that it was using the higher of the 2 speeds for the A/C.

 

Now I think that I need to have another HVAC tech come out and measure the blower speed.  Is that something that an HVAC tech should be prepared to do with any A/C service call?

[m_west5]

From what you described in your initial write-up, these are the two most common causes for your issue. System pressures should have been the first thing to check. It does not matter really what time of day to check it, but in the hottest part of the afternoon the head (high) pressure would be peaked. Then simply refer to the PT chart and verify the high and low pressures correspond to ambient temperature for your particular refrigerant R22, R410, etc. Think very small leak. They would also want to check the supply and return temp splits in your home.

As far as the blower motor speed rpm, your neighbor did check the correct board setting/configuration. That is good although it should also be checked by amp draw, run capacitor, and actual blade speed rotation (visual). Sluggish, noisy, dirty, etc. The PCB could also be flaky or have intermittent connections, etc. Not an easy job, but the correct way to do it. There are testers to check rpm's but whether they own one or not, is up to the individual tech. Not a necessity, but it definitely makes the job easier. 99% of the time it can be properly troubleshot by doing the above. I would advice you to go with a reputable company that is well established in your area. Keep in mind cheaper is not always best.

A good quality company will do all the above and more to properly repair your system and gain a happy and satisfied customer. Please let us know how it went and ask questions.

Edited October 27, 2015 by Radio Loco

[m_west5]

One more thought, your system may have a defrost control board too. Was this ever brought to your attention by one of the techs?

[m_west5]

"Are there other ways to clean the evaporator coil besides picking at it by hand? Maybe there's other foreign matter between the fins that we can't see."

Yes. An EVAP coil cleaner sprayed onto the entire coil could be used. This will foam up and "lift" the dirt out of the coil fins. Some are self rinsing, some you carefully hose off with water. Just verify that the condensate drains are clear and open to the outside. Do NOT use a condenser coil cleaner on the evap coil and vice versa. And follow the directions on the container exactly as written by the manufacturer.

Edited October 27, 2015 by Radio Loco

[ACtechGUY]

You Said you have a rheem condenser, But you never specified the evaporator coil brand . Assuming you also have a rheem  evaporator , then  Rheem tends to use a  W configuration on their evaporator coils that is all but impossible to clean in place.  The only option most times is to pump down the system and actually remove the evaporator coil from the case, take it outside and hit it with coil cleaner and semi high pressure water . You would be amazed how much crud gets trapped in a coil. 

To verify the evap is dirty , someone could take a static pressure reading after the furnace but before the coil, and after the coil. The literature for the evaporator will specify what the max static pressure should be. If it does not agree , then you have a clogged coil. 

 

That being said...... you have a 15 plus Year old coil  that  may be about to rust out and need to be replaced anyway. ( maybe not Though, if you are in that dry of a climate) .

 

I can help more if you can get a thermometer and some cheap refrigerant gauges  to let me know the system pressures and temperatures. 

 

Ps, the carrier furnace you specified has more than enough blower capacity for 3 1/2 tons of a/c , even if it is at the wrong low speed.  But like said above, if the capacitor is bad the motor may be spinning slower than expected or even stopping sometimes.  

 

There are alot of possible problems and alot of things to explore. 

 

good luck

Edited November 2, 2015 by ACtechGUY

[grasshopper #309287721]

One more thought, your system may have a defrost control board too. Was this ever brought to your attention by one of the techs?

 

I don't recall any of the techs mentioning a defrost control board.  But I've taken pictures of the control board in the furnace and I'll try to post them.

[grasshopper #309287721]

OK, I am struggling with the interface for uploading images.

 

Here's what it says in the "Help Topic: Gallery" (http://appliantology.org/index.php?app=core&module=help&do=01&HID=12&hl=upload):

 

Adding your Images

Clicking an upload link or button will take you to the media upload page. This is a two step process.
The first step is to select or create an album (or category) to upload the images into. Once the album or category has been set, you can upload images right away when the upload form reveals itself.
When you have uploaded the images you wish, you click the 'Review & Publish' button which will allow you to rotate the image or edit the image's details.

 

I'm not finding a way to create an album (or category).  I went into http://appliantology.org/gallery/category/2-members-gallery, but don't see an upload form or a way to create an album or category.

 

There's also this on the same help page:

 

The gallery can be used to upload images you wish to share with the community. To access it, click the "Gallery" tab at the top of any page.

Gallery Home Page
The gallery has two areas: Categories and albums. Administrators will create the categories that you can upload images into, or create albums within. If you have permission to create albums, you will be able to create them within the categories that administrators designate as accepting new albums. The homepage may show a feed of recent images, featured images, categories and/or recently updated albums, depending upon the administrator's configuration selections.

 

So do I have to request permission to create an album first and then I'll be able to create it and upload the photos?

[grasshopper #309287721]

I've uploaded my furnace control board pictures to "Samurai's File Dropbox" located here http://appliantology.org/concierge.  Not sure what to do next.  I don't see the photos in the member's gallery.

[smee123]

You Said you have a rheem condenser, But you never specified the evaporator coil brand . Assuming you also have a rheem  evaporator , then  Rheem tends to use a  W configuration on their evaporator coils that is all but impossible to clean in place.  The only option most times is to pump down the system and actually remove the evaporator coil from the case, take it outside and hit it with coil cleaner and semi high pressure water . You would be amazed how much crud gets trapped in a coil. 

To verify the evap is dirty , someone could take a static pressure reading after the furnace but before the coil, and after the coil. The literature for the evaporator will specify what the max static pressure should be. If it does not agree , then you have a clogged coil. 

 

That being said...... you have a 15 plus Year old coil  that  may be about to rust out and need to be replaced anyway. ( maybe not Though, if you are in that dry of a climate) .

 

I can help more if you can get a thermometer and some cheap refrigerant gauges  to let me know the system pressures and temperatures. 

 

Ps, the carrier furnace you specified has more than enough blower capacity for 3 1/2 tons of a/c , even if it is at the wrong low speed.  But like said above, if the capacitor is bad the motor may be spinning slower than expected or even stopping sometimes.  

 

There are alot of possible problems and alot of things to explore. 

 

good luck

Came across one of those w shaped coils recently.

Only way to get a look was to remove the blower and look thru the heat exchanger.. 

It had been randomly freezing in the summer even after fixing a leak near the condenser and them changing out the filthy filter.

 

So no surprise that the coil was filthy...

[ACtechGUY]

FYI to all helpful appliance techs This is not a refrigerator . This system has a carrier brand  GAS FURNACE, so no defrost board. a gas furnace will NEVER have a defrost board. LoL

 

 

[alamo1718]

Two things cause evaporator coils to freeze, airflow problem( too low) or refrigerant problem(too little).

 

You need some readings to get an idea of where to start looking for the problem. Since it's a gas furnace, temperature rise in heat will give a rough idea of airflow. Call for heat and put a thermometer in the duct work. One on the return, between the filter and the furnace, as close to the furnace as possible without drilling a hole in the furnace. If you have flex duct, just poke it in the duct. If you have metal ducts, you'll need to drill a small hole to insert the thermometer(in the duct). Record that temp. Use the same thermometer and take a temp reading of the supply air with the heat running. Wait until the temp has stabilized, stopped rising. Record that temp.  The supply air temp reading needs to be in the duct work also, close to the furnace. Do not drill a hole in the cooling coil case. You might drill into the coil, that would be very,very bad. The reason to work close to the furnace is that you lose some heat in the ductwork in both directions. 

You are looking for the temperature rise in the furnace, the difference between the readings. If the installers paperwork is still there, it usually gives temp rise ranges. If the paperwork is gone, there is a sticker behind one of the service panels, on the interior of the furnace that will give the acceptable ranges. If the temp rise is high, there is a low air flow problem. If this is the case, I would suspect the coil is still impacted with dirt. If the temp rise is normal or low, I would suspect low refrigerant level.  I'm pretty sure your temp rise range is 45-75. The way to read that is a rise as low as 45 degrees or as high as 75 degrees. 

 

If you call a technician, look for these readings: Temperature rise across the furnace,  manufacturer recommended temp rise range, TESP(Total External Static Pressure, think air pressure in the ductwork), Low side refrigerant pressure, High side refrigerant pressure, Superheat, Sub cooling, Outdoor dry  temperature, Indoor dry temperature, Indoor Wet bulb Temperature. If you find somebody that can measure TESP, you will be golden. It is the "air pressure" in the system. There is a chart for your system that will use TESP to give a pretty accurate indication of airflow. 

 

By the way,  how long has this been a problem? You said it was installed in 1998/6 and it worked for 3-4 years. Has it been acting up for the last 10 years or did this just start? 

 

Installing a 3/4 hp motor won't fix the problem.  I am pretty sure that's a 4 ton furnace with a 3 ton coil. The 3 ton coil needs 1200 CFM and the furnace on high can deliver about 1600 CFM. If the duct work isn't sized correctly, a larger fan will actually reduce airflow.