A/C start-up intermittent start up issue

[jp102]

I have a Rheem RGRM09 2 stage furnace with Carrier A/C unit. A couple of times this summer I've come home and the A/C compressor has been on, but the blower fan is not running. The system is iced up and when I shut the system down for ten minutes and turn it back on everything starts up and works ok. The system has an ECM blower motor with a power factor choke, not a start up cap.

The furnace is about 9 months old, the A/C unit about 10 yrs. Never had a problem with a heat call this winter, this is the first summer with the new blower. Since day one, when the blower starts up (heat or cold) it rumbles for the first 30 or so seconds. Other thing that doesn't make too much sense to me is that the compressor and blower start at the same time. I would expect the blower to come on, get up to speed and then the compressor to kick. Same thing with the heat call; the exchanger fires at the same time the blower starts.

If anyone has any thoughts on what might be the issue with the blower not starting, I'd greatly appreciate them. My initial reaction is to replace the power factor choke, but I really don't know much about them so I'm not sure if it would fix the problem.

[DonL]

Welcome to Terry's Forums jp102,

What is the Model of your Carrier A/C unit.

You may want to try to put your Thermostat / Controller in Fan Continuous Run mode when it gets in that screwed up mode to further diagnose your problem, and see if you can manually control the blower.

As far as the compressor and blower starting at the same time, That should not be a problem.


Good Luck on your project.


DonL

[jp102]

DonL - thanks. Don't have the model of the carrier unit with me, I'll get that tonight. Good suggestion with the continuos run mode. The thermostat is an Aprilaire with a circlating mode (turns fans on every 20 minutes).

[DonL]

The model number would help you greatly to get a better answer.

Different Models and Different ECM blowers will ramp up differently, and some are programmable. Depends on the design.

The thermostat Model also would help.

Have a great day.


DonL

[jadnashua]

On my variable speed blower, it starts up when the call for heat or cooling starts. The fan speed starts out slow, and ramps up over time and then ramps down after the call ends. how fast it goes depends on how long the call is as it changes based on time that it is running. Not sure how all brands work, but this is on my Trane stuff. Starting out slow helps in both heating and cooling, as a slow speed means the cold air in the duct during the winter doesn't blast you. in the summer, moving the air slower over the coil means it can dehumidify better. Ramping down at the end means you use all of the energy in the heating or cooling from the heat exchanger. A slow start also is much less obtrusive.

[jp102]

Furnace model Rheem rgrm09
AC model Carrier CD5AXW048
Thermostat Aprilaire 8466

Setup as 2 stage heat, 1 stage air. Not a variable speed furnace.

Thanks in advance

[DonL]

When you say "when I shut the system down for ten minutes and turn it back on everything starts up" are you using the thermostat to turn it off, or are you killing power to the unit ?

Are you using the "CIRC" fan mode ?


DonL

[jp102]

I'm killing power to the unit. I did not try turning off/on with the thermostat. The system will actually start right away (blower and ac unit) if flip the power switch off/on, but it just won't cool as I suspect the lines are iced up. I waited the ten minutes for the lines to un-freeze. The thermostat was in "cooling" mode according to the thermostat display.

Yes I'm using the CIRC fan mode.

[jadnashua]

If things freeze up, you may need to call for service. The refrigerant levels may be off. The blower may be running, but if the evaporator is covered with ice, no air can get through. Also, make sure the filter is clean...reduced air flow can cause it to get too cold and freeze things as can an incorrect refrigerant level.

[jp102]

Shut down by killing power. Did not try to use thermostat to shut it down. It will start up immediately (both blower and AC unit) if I kill and restore power however it won't start cooling as the AC lines are frozen up. Ten minutes was an approximation; one time it may have been fifteen, the other time 5. Basically just enough time to let everything defrost.

I use the CIRC fan mode.

[Gary Beach]

I have a Rheem RGRM09 2 stage furnace with Carrier A/C unit. A couple of times this summer I've come home and the A/C compressor has been on, but the blower fan is not running. The system is iced up and when I shut the system down for ten minutes and turn it back on everything starts up and works ok. The system has an ECM blower motor with a power factor choke, not a start up cap.

The furnace is about 9 months old, the A/C unit about 10 yrs. Never had a problem with a heat call this winter, this is the first summer with the new blower. Since day one, when the blower starts up (heat or cold) it rumbles for the first 30 or so seconds. Other thing that doesn't make too much sense to me is that the compressor and blower start at the same time. I would expect the blower to come on, get up to speed and then the compressor to kick. Same thing with the heat call; the exchanger fires at the same time the blower starts.

If anyone has any thoughts on what might be the issue with the blower not starting, I'd greatly appreciate them. My initial reaction is to replace the power factor choke, but I really don't know much about them so I'm not sure if it would fix the problem.

1st. If the unit is froze up, turn it off for about 24hrs. to be sure all the ice is cleared.
check the air filters, change them is any doubts, use new ones in this case to be sure they are okay.
If filters are not plugged up, and air flow is fine, call someone to check the charge on the unit.

That cooling coil can be plugged with ice, or partially plugged. That will cause it to ice over again. Also a technician can not be sure of the charge if there is any ice on that coil left.

[DonL]

If filters are not plugged up, and air flow is fine.

I do believe that that is the problem that is causing it to ICE up, The Blower is not running, and is causing it to Ice up.

jp102, I am still looking into the fan control system to see if I can help, or make a educated guess, as to why the blower is not starting.

It could be something as simple as loose wire, or may could be a blower relay. Or even blower speed not fast enough.

Did it ever operate correctly, after the Aprilaire 8466 was installed ?

After you do restart it will it continue to operate normally, or does it ice up again ?


Have a good day.


DonL

[jp102]

The reason the unit is freezing is because the blower is not coming on (or is prematurely shutting down) during a call for cooling. FIlters are ok, refrig levels ok. It has only happened three times during the summer (out of probably hundreds of call for cooling). AC has been on since late May and the three times I had the issue it was a fairly warm day and the failures have been weeks apart. Thermostat wiring is new and I have had no problem with the blower not coming on during the heating season so I suspect that wiring/loose connections are not the problem.

My current thoughts are that it could be one of the following:

1. Bug in the firmware or some other issue with the thermostat related to the CIRC feature.
2. Bug in the furnace firmware related to the call for cooling during a fan ON
3. Blower motor or power factor module
4. Power brownout/surge preventing blower from starting.

#1 in my mind is the leading candidate, #2 doubt it and #3 probably not as I would have had some heating call issues or more cooling issues. #4 not sure of as I would think a blower on signal would continue and start the motor throughout the cycle.

Next time it fails I will check the blower lead at the thermostat during the failure and trace it through the furnace, however I'd like to fix the problem before it happens again so I don't freeze my AC unit and have to replace it. I am surprised that the control board of the furnace allows for a cooling cycle to occur without seeing some feedback from the ECM motor.

Any other thoughts? Am I correct in my thinking of the above items?

Thanks again

[jp102]

DonL - thanks. Some of the replies are getting out of sync so bear with me if it sounds like I'm repeating myself.

Yes it has operated correctly with the Aprilaire 8466. The 8466 was installed with the furnace and the system has operated from Oct-April last year on heat, May to present on AC. Many, many calls for AC, only failed three times. Always in CIRC mode.

After I resart, the system continues to operate normally and does not ice up.

[DonL]

Did you set the dip switches on your Furnace controller to match the AC unit size ?

It sounds like your blower may be running slower than needed for your A coil size.
Then it ices up, if it has to run longer for higher outdoor temps.

Can you here the blower change speeds when you go from "AUTO" to "ON" ?
If not than your T-stat may have a wire in the wrong place, not letting the blower change speeds.

It looks like the blower runs at 4 different speeds.


DonL

[jp102]

DonL - I have SW1-5 ans SW1-6 set to ON/OFF (profile B) which gives 1600 CFM HI, 1200 CFM low which I believe matches the 4 ton AC unit specs.

Yes I can hear the blower changing speeds.

Question - when the AC frezes up, does or should the blower shutdown? Should the entire system shutdown when it freezes?

[DonL]

It should be set for 1600, on cooling.

And the whole system would shut down, not just the blower.

You may want to set for 1600. Then run the t-stat on auto.


DonL

[jp102]

Thanks. Maybe I'm chasing the wrong problem. I've been trying to figure out why the blower isn't starting, maybe I should be figuring out why the AC unit isn't shutting down when it freezes. Obviously I need to figure out why it freezes, but that might be another issue. Can you share any thoughts on the shutdown circuit of the system if it detects a freeze?

[DonL]

The blower could be running and it could be hard to tell, because when it freezes up there is no place for the air to go.

But for a 4 ton then you want to run the blower at least 1600, or it could Ice up.

As for the shutdown, I am not sure if that part works on the air side.
Could only be for heating.

With it being two different brands, that is hard to tell, if the controller even knows that it is iced up.

Wish I could have the answer, but I am not for certain.


I would start by upping the air flow, and your problem may be solved.


Enjoy your day.


DonL

[Runs with bison]

DonL - I have SW1-5 ans SW1-6 set to ON/OFF (profile B) which gives 1600 CFM HI, 1200 CFM low which I believe matches the 4 ton AC unit specs.

Yes I can hear the blower changing speeds.

Question - when the AC frezes up, does or should the blower shutdown? Should the entire system shutdown when it freezes?

I have the same 9 month old Ruud (same model number and equipment as Rheem). Check your flows on the ECM blower by reading the blinking red light in the little view port on the air handler (one blink = 100 CFM per p. 54 of manual.) This isn't the actual flow but represents the target speed call by the board. Mine is also paired with a 4 ton AC (new Rheem two stage AC.)

The manual states on p. 47 that the default for these is max flow, profile A, which is 2000/1500 cfm. That is how mine was set up IIRC (I've got notes on dip switch positions...but have misplaced them.) I've since dialed back with the optimization switch set (which is noted wrong in the manual per my recollection and testing--the manual is confused and confusing in this section) so that it is running about 1800/1300 to better dehumidify on low stage. I'll take a look at this tonight once we get back below 95 F. I might try setting it to B to see if any problems appear. To do that I'll have to reset the optimization switches to default.

My furnace also tends to start up a little noisily, haven't noticed the blower making the rumble in summer. I'll take a closer listen tonight. I believe the rumble in winter is from the furnace first firing up as I recall. Something to do with the sealed combustion and ID set up, maybe some baffle rattle. It actually became more noticeable when I had some of the side ports on the furnace blocked off (they weren't originally, but should have been.) There could be some sort of "critical speed" vibration on the blower at the lowest speeds, I suspected that. Since it doesn't stay in that mode more than a few seconds I haven't tried to follow it up.

At any rate, mine seems to be doing pretty well at cooling so far...while the old one was having trouble and approaching the point of siezing up.

Note that the default "FAN" circ. setting is very low for the blower if in the "low" setting (around 500-600 CFM I think.) I've reset mine to "high." Our 90k units are not in table for this on page 48. Even "high" is not that high--something like 1200 CFM I think I measured. So if this is being used for the blower speed when the 4 ton is running, it could be having trouble freezing up from low air flow. That could be the case if there is some sort of miswiring.

[DonL]

Note that the default "FAN" circ. setting is very low for the blower if in the "low" setting (around 500-600 CFM I think.) I've reset mine to "high." Our 90k units are not in table for this on page 48. Even "high" is not that high--something like 1200 CFM I think I measured. So if this is being used for the blower speed when the 4 ton is running, it could be having trouble freezing up from low air flow. That could be the case if there is some sort of miswiring.

Normally you would want the blower to run at 400 CFM per Ton of cooling, So what you are saying makes sense.

If all the system is a Rheem then the system should shutdown if it did detect a Iced up condition, Or at least increase the blower speed to at least 1600 CFM if it was in a dehumidifier mode and seen the was Icing.

Normally the compressor would also cut back if it decreases the fan speed and dehumidify on low stage.

Sounds like the outside unit does not know what the inside unit is doing.

Could be just a wiring problem between a Rheem and a Carrier, Wiring color code maybe.

Thank You for your info Runs with bison.


Enjoy Your Day.


DonL

[Runs with bison]

Sounds like the outside unit does not know what the inside unit is doing.

Could be just a wiring problem between a Rheem and a Carrier, Wiring color code maybe.

Thank You for your info Runs with bison.

You are welcome.

That's what it sounds like to me too, but since I've never run the wiring or done the controls on HVAC units I can't really take it past that.

Another thing I would check is the specific jumper for the AC type--SW12 should be set to ON for single stage cooling. Sounds like he's probably already done that.

[jp102]

Thanks guys. I've re-checked all the settings and configs and they are in agreement with your suggestions. The system runs only on the thermostat, no humidity sensor/control. Also since it is an older AC unit, there are only two wires running to the AC contactor (Y1 and C) so the outside unit is dumb.

Someone mentioned that the Rheem furnace detects an iced condition, does anyone know how it detects this? Also what does it do once it detects an iced condition; does it shut down blower, can it pull Y1 to low and override the thermostat's call for cooling thus shutting down the outside AC unit?

[DonL]

Good Morning,

I believe it detects the air flow, and knows something is not correct.

You should be connecting to Y2.
On Y1 the blower will only be running on low speed, and will ice up.

Y2 will turn the compressor off when the blower is not running.


Enjoy Your Day.


DonL

[jp102]

Thank you. I'll make the switch tonight

[DonL]

Thank you. I'll make the switch tonight

Please let us know how it works for you jp102.

After you switch over from Y1 to Y2 , I think your system will work a lot better for you.

Even save you money.


Have a great day.


DonL

[Runs with bison]

When you make the switch, I really encourage you to count the blinks on the red LED before and after you switch it. The LED blinks periodicaly when running, 1 blink = 100 cfm. The blinks are a little uneven at the start and end of the sequence so I might be off by 1 for the way I count them, but even if I am it makes it easy to compare before and after when changes are made.

Also, the rumble at start up on circ is definitely still there--seems to continue until it gets up to speed. I tested circ today and counted ~13 blinks on the "high" circ switch setting. That corresponds to the same flow as the 105k furnace in the table on p. 48 (where the 90k furnace is not listed.)

I've also gone to profile B, 1600 cfm, for my 4 ton AC to improve dehumidification on the low stage air (this will dial it back to 1200 cfm for 2 tons--it defaulted to 1500 cfm in low and I had cut it back 10% before with other switch settings that I've now reverted.) I've confirmed the low and high values with the LED blinks.

[Gary Beach]

DonL - thanks. Some of the replies are getting out of sync so bear with me if it sounds like I'm repeating myself.

Yes it has operated correctly with the Aprilaire 8466. The 8466 was installed with the furnace and the system has operated from Oct-April last year on heat, May to present on AC. Many, many calls for AC, only failed three times. Always in CIRC mode.

After I resart, the system continues to operate normally and does not ice up.

I would try eliminating that April air thermostat. See what that does. "Circulate Fan Mode means that the fan comes on for 10 minutes every 30 minutes for better indoor air quality plus reduces hot and cold spots within your home."
http://www.aprilaire.com/index.php?znfAction=ProductDetails&category=23&item=8466

I have seen these fail, and be miss-wired, or the setup program could cause this even. Go get an old basic thermostat and wire it in place of the April air. (Eliminate the April air all together for now). See what the A/C does without that.

[Gary Beach]

Thanks guys. I've re-checked all the settings and configs and they are in agreement with your suggestions. The system runs only on the thermostat, no humidity sensor/control. Also since it is an older AC unit, there are only two wires running to the AC contactor (Y1 and C) so the outside unit is dumb.

Someone mentioned that the Rheem furnace detects an iced condition, does anyone know how it detects this? Also what does it do once it detects an iced condition; does it shut down blower, can it pull Y1 to low and override the thermostat's call for cooling thus shutting down the outside AC unit?

Is it a Heat Pump? They detect ice in the Heat Pump mode, but normally not in A/C mode. Not unless it has an airflow switch in the air handler supply duct.

[jp102]

DonL - was wired to Y2 on control board (Y on thermostat)

Bison - counted the flashing red led, got 16 flashes = 1600 CFM

Gary - it's not a heat pump, there is no external sensor in supply duct. I'll try and dig up the old thermostat, replace the Aprilaire and see what happens.

I still do not understand if a Rheem RGRM 90k will shut down the blower if it detects an iced condition. If anyone knows the answer to this question, please let me know as it will give me an indication of where to troubleshoot. Right now I still do not know if the blower is not starting; hence causing the iceup. Or if the iceup is occuring and the system is shutting down the blower.

Also while counting the flashing led I noticed that the status light was steady on. According to the manual this is a "normal fualt detected". Anyone know what this means?

[Runs with bison]

Bison - counted the flashing red led, got 16 flashes = 1600 CFM
Does it do that both when it is in auto and when it is set with fan on (or is in the middle of or interrupted by Aprilaire calling for the blower to run?) I even wonder if the Aprilaire in the timed circulation mode is shutting off the blower at the end of its time...even if the AC compressor is still running. May be some sort of logic problem with the Aprilaire circulation mode. By checking blink counts with and without circ you might be able to catch it when it does something unexpected. For example, if the blink count is reduced by the Aprilaire when it kicks to "circ" mode in the middle of an AC call that would be a problem.


I still do not understand if a Rheem RGRM 90k will shut down the blower if it detects an iced condition. If anyone knows the answer to this question, please let me know as it will give me an indication of where to troubleshoot. Right now I still do not know if the blower is not starting; hence causing the iceup. Or if the iceup is occuring and the system is shutting down the blower.

I'm not seeing anything in the furnace/air handler manual about what it can/does detect when in AC mode. It appears that it is relying on the AC for that bit of logic. Indeed, the manual for my AC unit talks about high and low pressure protections built into the AC control board's logic and it has its own 7 segment LED display to provide codes. Your older AC might not trip the compressor on high discharge or low suction pressure.

My layman's conclusion is that the furnace/air handler will not detect the icing. So then we get back to the root question (full circle): is the thermostat or a wiring issue causing the blower to sometimes shut off or go to low flow? Or is the AC freezing with normal air flows?

What I suggest is measuring the blower LED blinks in various situations in circ mode...1. With the AC turning on while it the fan/blower is on for circ. 2. With the AC shutting off while the fan/blower is on for circ. 3. With the circ timer shutting off while the blower is supposed to still be running while the AC is running. 4. With just the blower running for circ. (To really make the difference obvious, you might want to set the fan dipswitch back to "low" during the tests...the low fan flow is so low that you won't have any doubt on the difference in blink count. If the circ timer on the tstat is overriding the normal blower speed call in some fashion then that would be a problem.)


Also while counting the flashing led I noticed that the status light was steady on. According to the manual this is a "normal fualt detected". Anyone know what this means?

My response is in the other thread. As best I can tell this indicates a normal operation state...although the wording they chose for that confuses the hell out of me too!

[jp102]

I installed a freeze protection control switch from Honeywell that breaks the Y circuit to the compressor if the coil goes below 36 F. This will prevent the system from freezing and blowing out components, although it doesn't solve the root cause of the issue. I am in the process of making a small break out box to manually control and monitor the C, G and Y at the furnance to try and capture the issue as well as measuring the blower blinks for the various situations described above. Probably won't mess with it this week as we are 100+ today. Last thing the system needs right now is experimentation.

[DonL]

Hello jp102,

Is your low pressure suction line sweating all the way back to the compressor.

If it is not then, Maybe the refrigerant is low.

Let us know how You come out on your project. Never give up...


Have a great day.


DonL

[jp102]

I'm getting a bit closer. The freeze protection switch cutoff the Y circuit yesterday at 36 degrees to prevent a freeze up. The Rheem RGRM 90k control board had both green LED's on solid and the red LED blink count was 16, however the blower was not working. SO it appears that the problem is within the blower motor or main control board of the furnace. I tried to get the furnace panel off without tripping the power switch, but was unsuccessful and the reset of the power restarted the blower. I've put some duct tape on the swtich so that I can open the panel next time without resetting and then I can start tracing the fault.

Anyone got any further ideas? Anyone seen this type of behavior with a Rheem?

[Runs with bison]

Nice work. Sounds like it is time for a warranty call.
1. Seems strange that the board isn't recognizing that the ECM is not running, yet the blink codes for the "integrated furnace control" board seem to indicate that it thinks it (the board) is operating normally.
2. The ECM's own controls must be telling it to shut down or it has some sort of interruption in its communication with the IFC that the IFC is unaware of that is leading it the ECM to shutdown.
3. If the ECM's own controls are telling it to shutdown the question is why? Is it some sort of overheat condition for the blower motor?

Good luck on this. This is the one fear I had when going to the ECM blower, that it would fail in some fashion due to increased complexity. But this could be even worse in that it is an intermittent failure making identifying the culprit harder.

Kinda wonder if there is a loose connector in the plug to the blower.

[jp102]

The saga continues....

The fault happened again this weekend and I was able to get into the blower compartment. LED was blinking 1600 CFM, Y and G had 24v and blower had power. Looks like the problem is in the ECM blower.

As I was pondering what would cause a motor to shutdown/overheat it dawned on me to check the CFM rating of my duct work. Turns out I only have a 8"x22" return and a 8x22" supply. From what I can determine, a 8x22" rectangular duct is only rated for 840 CFM, slight less than the 1600 CFM I'm trying to push/pull.

Does anyone have thoughts on ECM's and inadequate ducts?

[BobL43]

The saga continues....

The fault happened again this weekend and I was able to get into the blower compartment. LED was blinking 1600 CFM, Y and G had 24v and blower had power. Looks like the problem is in the ECM blower.

As I was pondering what would cause a motor to shutdown/overheat it dawned on me to check the CFM rating of my duct work. Turns out I only have a 8"x22" return and a 8x22" supply. From what I can determine, a 8x22" rectangular duct is only rated for 840 CFM, slight less than the 1600 CFM I'm trying to push/pull.

Does anyone have thoughts on ECM's and inadequate ducts? a motor that runs a squirel cage blower will draw less current than normal when the blower air flow is restricted. Possibly the electronic drive module for the motor is looking for current within a certain range according to how it is programmed and will fault out if it is substantially less. Also, and I am no HVAC specialist, the reduced air flow across the evaporator coil will cause it to ice up, as mentioned in previous posts here.

[DonL]

I would look for a bad solder connection on the fan motor control relay.

Or a loose wiring connection.