A/C start-up intermittent start up issue

**Runs with bison** · 07-20-2011, 05:50 PM

Originally Posted by jp102

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** · 07-21-2011, 09:01 AM

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** · 07-21-2011, 04:04 PM

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** · 07-25-2011, 05:06 AM

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** · 07-25-2011, 07:39 AM

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** · 08-01-2011, 05:13 AM

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** · 08-01-2011, 07:28 AM

Originally Posted by 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?

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.