HVAC guys. Have a question for you.

[maccrazy2]

Hey everyone. I have a question for you hvac guys. I installed an amana 95% efficency furnace and a 1.5ton ac in my house 2 years ago. It has worked fine untill I started to use the ac this summer. The airflow out of the vents is less than before. I changed the filter and no change. I inspected the air inlet and there are no restrictions. The air outlet is not restricted from what I can see with a mirror in several registers.
The other night I went into the room to look it over again and the low side copper tube had ice/snow built up on it where the copper was exposed before the foam insulation covers the tube. It has never done this before. It seems to me the blower is not moving enough air thru the evap coil and the evap is icing up after running all day.
I put my wind meter by several registers when I started it up tonight after not running the unit all day. The outlet temp was 70deg and the house is 72.5deg. the wind meter did not register at all. I had one register cover removed and stick the meter up into the center of the vent and I get 2mph reading max. It never moved air like a jet engine but before you could feel airflow and now there is next to nothing.
I verified the fan blades were not damaged in any way and not covered in lint or anything. It has never been run without a filter and they are changed regularly. Also, I have been using the better quality pleated ones not the cheap blue mesh ones.
The owners manual says the fan motor is preset to the high blower speed. I verified the correct wire (black) is run to the correct spot on the controll board for high speed blower/cooling.
I can only figure the issue has to be the blower not running full speed or something blocking airflow over the evap coil. Being as it has never been run without a filter and I had the vents cleaned when I put the units in. I doubt it is anything built up on the evap coil. So, can the blower motor operate but not run full speed when powered thru the high speed wire? I just need a plan of attack before I start tearing into things.

 

[maccrazy2]

Re: HVAC guys. Have a question for you.

 

[ADVAUTO5488]

Re: HVAC guys. Have a question for you.

Looks like your ac unit is low on refrigerent. My brother in law is a hvac guy. I had the same problem. The A coil would freeze solid and the low side line would be white with frost. I am an auto tech, and I thought he was crazy. I added 3 pounds of refrigerent to my system and it works great. I sealed the brass caps on the shut off ports. He said all the new units they put in leak at these ports. Hope this helps. This looks exactly like the problem I had.

 

[The Mechanic]

Re: HVAC guys. Have a question for you.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ADVAUTO5488</div><div class="ubbcode-body">Looks like your ac unit is low on refrigerant. My brother in law is a hvac guy. I had the same problem. The A coil would freeze solid and the low side line would be white with frost. I am an auto tech, and I thought he was crazy. I added 3 pounds of refrigerant to my system and it works great. I sealed the brass caps on the shut off ports. He said all the new units they put in leak at these ports. Hope this helps. This looks exactly like the problem I had. </div></div>
This is what is wrong. You are low on freon and you have a frozen evap core. In other words if you were to look at the "radiator" up in the attic it would be a big ice cube that will not be able to get air through it.

Ideally someone should have given an accurate charge and put that weight of freon on the unit (heat pump). Otherwise you need a pro to "chase the frost line" and give it a proper charge and of course properly test it for leaks.

 

[The Mechanic]

Re: HVAC guys. Have a question for you.

Forgot to add. You can verify this by letting the A/C unit defrost by turning it off for about 4 hours or more and turn on the heat and you will get air flow. Turn the A/C on and the flow will slow down as the unit frosts up.

 

[maccrazy2]

Re: HVAC guys. Have a question for you.

I think I forgot to mention, the airflow does not change if the unit is started warm after sitting all day.
I have a gauge set and a 30lb jug of R22. I am an auto mechanic so I have the ability to charge and leak test. I will have to brush up on the superheat readings on my gauges as I don't normally use those on cars.

 

[The Mechanic]

Re: HVAC guys. Have a question for you.

Understand. I am an auto tech also but have a 608 and 609 licensing. A/C stuff is really simple. I have an electronic sight glass from Matco I think and if you use it enough you can get pretty close to it being just like a visual sight glass. If you have no flow after it has been off all day than I will have to say you either have a huge amount of frost that can sometimes bee seen if the condensation drain is visible and does not go into a sink drain. Otherwise you have a bad fan or dirty evap core.

 

[Queequeg]

Re: HVAC guys. Have a question for you.

Mac, there is another possibility, much simpler and less costly and the solution involves half of what Mechanic suggested.

When the A/C is run too long and too low, the evaporator coil will ice up. This occurs frequently here in the sunny, sultry south even with the freon pressure right on the money.

The solution for this problem is to turn the unit off and let the evaporator thaw out. In the more modern units with de-humidification the freeze up is less common but can still happen if you prefer to live in a meat locker!

As to freon, the only way to know the pressure is with the gauges.

 

[rrflyer]

Re: HVAC guys. Have a question for you.

If the fans not kicking on and pusshing the air i could see the pipe freezing.

BTW...we just had two new units put in our house along all new ductwork.

We were told to use cheap filters and change them monthly...the thick"better" ones block more airflow.

 

[vferguson3006]

Re: HVAC guys. Have a question for you.

Without getting too technical, it takes 400CFM of air passing over/through the evaporator to keep the coil from icing up, your 1.5 ton unit needs a minimum of 600CFM.
The best way to defrost your coil is to turn the thermostat subbase switch marked "FAN" from the auto position to ON, turn the system switch on the subbase to OFF. This will start the fan and compressor will stay off. Find the condenste line outlet exiting the house, or into a drain, or into a condensate pump, when there is no more water coming from the condenste line, the coil is free of ice.
If you have little or no airflow at this point, you have a restriction in the ductwork, fan issues, in other words an airflow problem.
If you have airflow, start the unit's compressor back up, if it starts to frost within minute's it's a refrigerant problem.
The evap. coil should be 40* with 55* discharge air with a suction pressure of 68#, if it drops below 57.5# because of lack of air flow or low on refrigerant it will ice up.
JOE

 

[Queequeg]

Re: HVAC guys. Have a question for you.

In many units, the air handler itself can be visually inspected once the filter is removed. Slide it out and look at the evaporator coil to see if it is iced up.

Vferguson nailed it!

 

[Gruff]

Re: HVAC guys. Have a question for you.

Evaporator coils freeze up because they are not absorbing enough heat from the return air to keep them thawed out. This is most commonly caused by one (or more) of two things. Low freon charge, or low air flow across the evaporator coils. A good HVAC guy can diagnose your problem in in a few minutes. I'm school trained by Carrier for large bus and truck systems, but I have a maintenance agreement with a HVAC company to service my home system twice a year even though I could do it myself. It only costs about $150 a year and I feel it is money well spent.

 

[maccrazy2]

Re: HVAC guys. Have a question for you.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: vferguson3006</div><div class="ubbcode-body">Without getting too technical, it takes 400CFM of air passing over/through the evaporator to keep the coil from icing up, your 1.5 ton unit needs a minimum of 600CFM.
The best way to defrost your coil is to turn the thermostat subbase switch marked "FAN" from the auto position to ON, turn the system switch on the subbase to OFF. This will start the fan and compressor will stay off. Find the condenste line outlet exiting the house, or into a drain, or into a condensate pump, when there is no more water coming from the condenste line, the coil is free of ice.
If you have little or no airflow at this point, you have a restriction in the ductwork, fan issues, in other words an airflow problem.
If you have airflow, start the unit's compressor back up, if it starts to frost within minute's it's a refrigerant problem.
The evap. coil should be 40* with 55* discharge air with a suction pressure of 68#, if it drops below 57.5# because of lack of air flow or low on refrigerant it will ice up.
JOE </div></div>
Joe. I can leave the unit off all day and then turn it on and there is airflow but not in the volume it had last summer. I can barely feel any air at the vents unless I get to within 8-10 inches from a register and then it is very weak. I have to run the ac all day long and later in the evening the low side line will frost up on humid days like in the pictures. It takes aprox 7-8 hours before this happens. I am leaning twards a fan motor not running at full high speed. if that is possible. I do not really work on AC motors so I am not sure how a multi speed motor is wound or how to properly test it.
Other than that a restricted evap. Once I remove the fan I can look up there and see if the fins are clean.
I will double check the units freon charge but I suspect this is more of an airflow issue due to the weak flow from startup. I will put the gauges on it tonight when I get home.
Thanks everyone for the help.

 

[The Mechanic]

Re: HVAC guys. Have a question for you.

All the residential A/C I have ever seen use a one speed motor (because it is the cheapest way to go). Is the unit in the attic? If it is just climb up there and make sure you don't have a piece of ducting missing or maybe even some tape (yes sometimes they seal leaks with duct tape) has come off and you will be able to feel all the air pumping out of the hole or crack. You have to get kinda hands on. If it is a motor and you are comfortable with sharp sheet metal and a/c voltage you can replace that motor with one from a local supplier like grainger. Just take the motor with you. I have a little inductive voltage checker I always keep with me it is cool as heck and not to expensive. Make sure to check the tool first for correct function and then test for voltage with the system on to verify you have disconnected the units power.
http://www.fluke.com/fluke/usen/electrical-test-tools/electrical-testers/fluke-1ac-ii.htm?PID=56048

 

[vferguson3006]

Re: HVAC guys. Have a question for you.

The last post the Mechanic is right. It [without seeing it first hand] appears to be a airflow problem so far. With a 95% furnace I assume it is a HighEff. Gas Heat/A/C system.
Usually they have 2 or 3 speed PSC motors, with an electronic board that auto selects speed based on Heat or A/C mode input from the T-stat.
So, the motor is either direct drive or belt.
the motor most likely is direct drive.
the motor should have a small metal oil filled can like electrical thing mounted on the motor housing or 2 wire leads coming from the motor to it.
The other motor leads, if you have a comb. of 4 or 5 wires, usually [depends on whose equip. it is] white, black, purple,
maybe 2 brown going to the metal can, and a blue and red it is a multiple speed motor.
Black/White usually is High speed, the blue and red are selected by the electronic board base on mode. [Blue usually med. speed, Red usually low, rarely used.
Could be the motor, board, of as the Mechanic suggested inspect all the ductwork you can get to with a flashlight to see if anything has come disconnected and you actually air conditiong the attic.
It's airflow dude, play detective.

 

[wfjames22]

Re: HVAC guys. Have a question for you.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: The Mechanic</div><div class="ubbcode-body">All the residential A/C I have ever seen use a one speed motor (because it is the cheapest way to go). </div></div>

I dont know how many you have looked at, because none of them that I have seen are single speed (blower motors). All of the ones that I have seen/replaced have multiple speeds (3 typically, High, Med, Low). They use different speeds for heat vs cool.

It sounds like you are low on refrigerant or have low/no airflow across the coil, as has already been stated. Your system doesnt have to be very low to freeze up in some circumstances. If you can see that the intake side of the evaporator coil (on top or end of furnace/airhandler) is clear, then you most likely have an insuficient refrigerant charge if your blower is operating. These are the two most likely scenarios, 99% of what we see causing units to freeze up everyday. Be sure that your system is R22 and not 410A, before you try and test/charge it.

 

[vferguson3006]

Re: HVAC guys. Have a question for you.

In my earlier post the pressures I referenced are typical of R-22 refrigerant, the unit is 2 yrs. old by your estimate, it may be either refrigerant. [A left over R-22 system]
The nameplate data will identify the refrigerant in your system, if it is in fact R410a, you will have to call an HVAC contractor to test pressures. much higher operating pressures associated with R410a takes special tools to test.
You can still inspect all and everything you can get to that is part of the airflow, or lack of enough airflow before you call that HVAC sub-contractor.
JOE

 

[The Mechanic]

Re: HVAC guys. Have a question for you.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wfjames22</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: The Mechanic</div><div class="ubbcode-body">All the residential A/C I have ever seen use a one speed motor (because it is the cheapest way to go). </div></div>

I dont know how many you have looked at, because none of them that I have seen are single speed (blower motors). All of the ones that I have seen/replaced have multiple speeds (3 typically, High, Med, Low). They use different speeds for heat vs cool.

It sounds like you are low on refrigerant or have low/no airflow across the coil, as has already been stated. Your system doesnt have to be very low to freeze up in some circumstances. If you can see that the intake side of the evaporator coil (on top or end of furnace/airhandler) is clear, then you most likely have an insuficient refrigerant charge if your blower is operating. These are the two most likely scenarios, 99% of what we see causing units to freeze up everyday. Be sure that your system is R22 and not 410A, before you try and test/charge it. </div></div>
I have been limited to the units in my complex, all the same units, and a few friends units that were maybe 20 years old or more so my experience with different manufacturers is very limited. My experience is mostly a knowledge of basic install, a very good working knowledge of electricity ac and dc and a high level of understanding pressures as a diag aid. Worked on refers with my family biz etc. Give me a set of gauges and environmental data and I can move a mountain.

I will look into the variable speed motors and there functioning. I always want to keep up to date, even if I don't do residential or commercial a/c except for automotive.

 

[oldgrayone]

Re: HVAC guys. Have a question for you.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: The Mechanic</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ADVAUTO5488</div><div class="ubbcode-body">Looks like your ac unit is low on refrigerant. My brother in law is a hvac guy. I had the same problem. The A coil would freeze solid and the low side line would be white with frost. I am an auto tech, and I thought he was crazy. I added 3 pounds of refrigerant to my system and it works great. I sealed the brass caps on the shut off ports. He said all the new units they put in leak at these ports. Hope this helps. This looks exactly like the problem I had. </div></div>
This is what is wrong. You are low on freon and you have a frozen evap core. In other words if you were to look at the "radiator" up in the attic it would be a big ice cube that will not be able to get air through it.

Ideally someone should have given an accurate charge and put that weight of freon on the unit (heat pump). Otherwise you need a pro to "chase the frost line" and give it a proper charge and of course properly test it for leaks. </div></div>

Listen to these guys. You are low on charge causing the low side to drop low in pressure which is causing the saturation temp on the freon be lower. Give it a squirt of juice and your problem will go away.

 

[maccrazy2]

Re: HVAC guys. Have a question for you.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: vferguson3006</div><div class="ubbcode-body"> if it starts to frost within minute's it's a refrigerant problem.
The evap. coil should be 40* with 55* discharge air with a suction pressure of 68#, if it drops below 57.5# because of lack of air flow or low on refrigerant it will ice up.
JOE </div></div>
Joe. I put the gauges on tonight. ambient air temp was around 85deg. The low side psig was 34psi high side psig 150. If I understand correctly that should give an evaporator temprature of around 11deg.
So I need to add refrigerant untill the low side reads 68psi which on my gauge shows a temp reading of aprox 38deg. is this correct? Based on the above numbers.
This ac unit came precharged and the line run was short enough that according to the factory it did not need extra charging when I installed it. I know I put the gauges on it after install but I did not record the readings so, I don't know what they were at the time of install.

 

[Gruff]

Re: HVAC guys. Have a question for you.

The head (high side) pressure depends on the TEMPERATURE at which the refrigerant (R-22) condenses in the condenser (outdoor coil). Add 15 to 25 degrees F to the outdoor temperature (say 90+15=105 and 90+ 25=115) and look at the TEMPERATURE information for R-22 on the gauge (green ring of numbers).

THE HIGH SIDE NEEDLE SHOULD POINT TO A TEMPERATURE BETWEEN 105 AND 115 (in the green ring of numbers) AND THE PRESSURE IS READ ON THE BLACK RING OF NUMBERS FOR PRESSURE.

The suction pressure depends by the TEMPERATURE of the boiling (evaporating) refrigerant (R-22) in the evaporator (indoor or cooling coil). This temperature should be about 35 to 40 degrees F below the Return Air temperature. IF the return temperature is 75 the evaporating temperature of the R-22 should be between (75-40=35) and (75-35=40).

THE LOW SIDE NEEDLE SHOULD POINT BETWEEN 35 AND 40 DEGREES (in the green ring of numbers) FOR R-22 AND THE PRESSURE IS READ WHERE THE NEEDLE POINTS ON THE BLACK RING OF NUMBERS FOR PRESSURE.

Note: It takes about 8 to 10 minutes of running before pressures stabilize to get accurate readings.

 

[vferguson3006]

Re: HVAC guys. Have a question for you.

Looks like you are on to something on the refrigerant side.
85* ambient with a 30*td across the condenser, if it is clean should give you a 240#head with the proper charge.
You are correct on the evap. reading, it would appear it is starved for refrigerant, and at 11* would ice up in a matter of hrs.
68.5# low side is a 40* evap., so right on there.
Again if the evap. is clean, and airflow is correct.
So, 68 to 69# on the low side and with a 85* ambient and 240# on the high side with a 85* ambient.Precharged tubing, precharged evap. and holding charge in the condenser usually has enough refrigerant for [depends on the mfr.] 15' or up to 25' of suction and liquid line.
If you are going to add R-22 yourself to the system, only add 8oz at a time, assuming you have some method to weigh the refrigerant in. Watch your pressures come up, with each addition of refrigerant.
The best method would of course, recover and recharge with the prescribed exact charge recommended by the mfr.
Hope this helps, JOE

 

[The Mechanic]

Re: HVAC guys. Have a question for you.

Here is a pdf for temp to pressure.
http://hvacsuite.com/R-22_TP_chart.pdf

Since you have an issue with the unit make sure when you are adding freon to let the system normalize for several minutes, the longer the better so you have a good accurate reading. Also if you start getting the frost on the line as you add refrigerant look at how the frost will melt as you are adding freon showing that you are raising the temp above freezing at that point.

I started to really get into the pressure temp relationship when R12 started to get real expensive and you had people putting other things in the bottles like propane. If you take the temp pressure chart you can see if it is pure freon or some blend that could be dangerous. You can also see if you have air in the system or low charge from its resting pressure.

 

[vferguson3006]

Re: HVAC guys. Have a question for you.

I still run into HVAC/R techs. that routinely "top-off" a system that is low on charge with another refrigerant.
Now you have a blend with P/T relationship not to be found on anybodys chart, and no way of knowing what the refrigerant %'s are, plus none of the supply houses want to take back mixed refrigerant.

 

[The Mechanic]

Re: HVAC guys. Have a question for you.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: vferguson3006</div><div class="ubbcode-body">I still run into HVAC/R techs. that routinely "top-off" a system that is low on charge with another refrigerant.
Now you have a blend with P/T relationship not to be found on anybodys chart, and no way of knowing what the refrigerant %'s are, plus none of the supply houses want to take back mixed refrigerant.</div></div>
So what do you do? Recover to a "waste" tank evac and full charge?
That would really piss me off. With the automotive stuff it is just to dang easy. Hook up machine set to automatic hybrid or not, set charge weight and push go. Come back after working on different car or truck and "BAMM" recovered weight and charge weight set. Check pressures and temp, flag it and park it. Easy money.

 

[vferguson3006]

Re: HVAC guys. Have a question for you.

As long as you are honest, and mark the recovery cylinder as "mixed refrigerant" the wholesaler will take it back.
When they send it to the reclamation facility, they will anyalize the contents and incinerate it. [which is apparently the only way to dispose of it and comply with EPA]
The kicker, the cost to dispose of the refrigerant because of some dopes mixing it is now passed back to/thru the wholesaler to the sub-contractor. So the techs. go home at 5'oclock and the business owner pays for their mistake.
Oh, they get their ass chewed out, and they pay attention to detail for awhile, but sooner or later because everybody is so busy, it will happen again.
JOE

 

[Gruff]

Re: HVAC guys. Have a question for you.

We have a machine we hook up to each system we work on that identifies what is exactly in the system before we do any work. It tells us what percentages of whatever is in there such as which refrigerant, if it has air in it, or if it is some kind of blend or if propane is in it. We then tell the owner of the additional costs involved because some jackass put Hotshot or some other crap in his system. Some of the systems on the big touring buses have as much as 24 to 30 lbs of refrigerant and when it is contaminated, costs big bucks to make it right.

 

[maccrazy2]

Re: HVAC guys. Have a question for you.

I think it is working now. I charged it and let the reading stabilize. Low side set to 68psi. high side was at 180. My vent temp is 59 deg in the basement vent that I checked after several hours of running the AC.
My vent airflow seems normal as well. The only conclusion I have come to on that is I must have had the thermostat programmed wrong so the ac kicked on during the day and iced up the evap before I got home and checked the airflow with my wind meter. I thought it had been off all day but I suspect I was wrong about that.
I did switch to the cheaper blue filters but when I was measuring speed I had removed the filter so I know that was not the problem. It was hard to wrap my head around how the low charge was causing freeze up. In cars low charge = insufficent cooling not frozen evap.
Now my big concern is locating the leak and what to do with it. The 4 joints I connected are dry and clean. I took the cover off the condensor and cleaned the fins and did not see any sign of oil anywhere on the core, lines or compressor. I cannot see the evap core without removing duct work. I think I will see how long the system stays working and figure out if I need to chase it any further. I do not know for certain that the charge was right from the get go but, the unit did work fine all last summer so I have to assume there is a tiny leak somewhere.
I will need to find my old R12 stuff so I can add some dye to the system if I have to start chasing the leak.

Thanks everyone for all your help on this. If you ever need car help feel free to contact me and I will be happy to return the favor. As always, shooters have never failed to help when I need it. Thanks again. Chris.

 

[The Mechanic]

Re: HVAC guys. Have a question for you.

Actually a low charge will also freeze up the evap core just like your home system. You may want to check compatibility of refrigerant lube of R12 with R22 or R401 Whatever you system has.
When you study the pressure temperature chart it is really easy to get the temp you want just by making sure the pressure is what you want. Humidity plays a huge part. Each one of the different refrigerants have different pressures to get the same temp just that some are more efficient at doing it at colder temps for refer units.
Refrigerent Oil guide

Refrigerent oil guide

 

[maccrazy2]

Re: HVAC guys. Have a question for you.

Thanks for the link.
I could see a car ac freezing up if it did not have a low side cycling switch or a malfunctioning expansion valve. I just normally see short cycling compressors or no output thru my shop.