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A/C start-up intermittent start up issue
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.
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
Don't pay someone to do a job fast, when you can do a half-fast job yourself.
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).
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
Last edited by DonL; 07-11-2011 at 08:25 AM.
Don't pay someone to do a job fast, when you can do a half-fast job yourself.
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.
Jim DeBruycker
Important note - I'm not a pro
Retired Defense Industry Engineer
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
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
Don't pay someone to do a job fast, when you can do a half-fast job yourself.
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.
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.
Jim DeBruycker
Important note - I'm not a pro
Retired Defense Industry Engineer
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.
1st. If the unit is froze up, turn it off for about 24hrs. to be sure all the ice is cleared.Originally Posted by jp102
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.
Last edited by Gary Beach; 07-12-2011 at 04:48 AM.
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
Don't pay someone to do a job fast, when you can do a half-fast job yourself.
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
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.
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
Don't pay someone to do a job fast, when you can do a half-fast job yourself.
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