A/C start-up intermittent start up issue

Discussion in 'HVAC Heating & Cooling' started by jp102, Jul 11, 2011.

  1. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,127
    Location:
    Houston, TX
    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
  2. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    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.
  3. jp102

    jp102 New Member

    Messages:
    20
    Location:
    Michigan
    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?
  4. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,127
    Location:
    Houston, TX
    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
    Last edited: Jul 14, 2011
  5. jp102

    jp102 New Member

    Messages:
    20
    Location:
    Michigan
    Thank you. I'll make the switch tonight
  6. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,127
    Location:
    Houston, TX
    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
  7. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    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.
  8. Gary Beach

    Gary Beach HVACR tech

    Messages:
    4
    Location:
    Nixa, MO
    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.
    Last edited: Jul 16, 2011
  9. Gary Beach

    Gary Beach HVACR tech

    Messages:
    4
    Location:
    Nixa, MO
    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.
  10. jp102

    jp102 New Member

    Messages:
    20
    Location:
    Michigan
    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?
  11. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    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'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.)

    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!
  12. jp102

    jp102 New Member

    Messages:
    20
    Location:
    Michigan
    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.
  13. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,127
    Location:
    Houston, TX
    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
  14. jp102

    jp102 New Member

    Messages:
    20
    Location:
    Michigan
    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?
  15. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    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.
  16. jp102

    jp102 New Member

    Messages:
    20
    Location:
    Michigan
    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?
  17. BobL43

    BobL43 DIY Senior Member

    Messages:
    1,792
    Location:
    Long Island, NY
    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.
  18. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,127
    Location:
    Houston, TX
    I would look for a bad solder connection on the fan motor control relay.

    Or a loose wiring connection.
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