Bad thermostat or???

ajbeckerhead

I have a Rheem Air handler that is connected to a Rheem A/C Heat pump. There is also a hydronic coil that is mounted in front of the air handler and piped to my boiler. I have a Braeburn 5220 thermostat controlling the system. It works fine for the cooling season but is giving me trouble when in heat mode. The air handler fan will just randomly start for no reason. There is no call for heat at the time. The only way to stop the fan is to turn off the thermostat and turn it back on. This is sometimes successful and other times not. Sometimes I have to pull thermostat off of mount and let it sit to get it to behave again. I spoke with Braeburn tech support and they thought I may have a shorted wire (maybe from mouse damage) that would make this occur. I disconnected the wires at thermostat and air handler and checked with VOHM meter all wires were open - no sorts indicated.
I was wondering if anyone has gone through similar circumstance? I suspect the thermostat is bad but don't want to get fooled into buying new thermostat for no reason.

Thanks for the help!
Andrew

Peter_26

I just looked up the user manual and you need to verify that fan control mode is set to AUTO as described below. If it is set to CIRC then you will see the unwanted operation you described in your post. Hope that helps.

Setting the FAN Control Mode
The Fan Control has 4 modes of operation – AUTO, ON, CIRC and PROG. The mode can be selected by pressing
the FAN button to scroll through the different modes.
NOTE: Depending on how your thermostat was configured, some fan modes may not be available.
AUTO The system fan will run only when your
heating or cooling system is running.
ON The system fan stays on.
CIRC The system fan will run from time to time
to help circulate air and provide more
even temperatures when the heating or
cooling system is not active.
PROG The system fan will function in the
AUTO or ON modes depending on your
program schedule.

ajbeckerhead

HI Peter Thanks for the reply. Yes, it is in the AUTO mode as you describe. It works fine in A/C mode but not in the heat mode. So far this year it has been behaving. It is damn nuisance though when it happens in the middle of the night and blows cold air all over you..brrrr

pedmec

Make sure the aquastat is wired correctly on the coil and that your not getting ghost flow in the piping. could be turning on the fan because its getting hot water in the coil during the off cycle. bad flochek at boiler maybe

EdTheHeaterMan

If the air handler was not designed for a hydronic coil to provide heat, then the addition of the Hydronic coil was an add on. There is no "standard wiring" for doing that. It takes someone with electrical control design experience. Not every standard HVAC tech or electrician can handle this task. You may be experiencing a situation where there is a strap on aquastat controlling the fan. The conventional logic is when the coil has hot water in it, the fan should operate. When the coil cools off, (and there is no other call for heat or cooling from the heat pump) the fan will stop. This is pretty sound logic until the attic gets hot OR THERE IS GHOST FLOW FROM A HOT BOILER and the water in the coil become hot enough from attic ambient temperature to operate the fan. I have come across this design and this problem from time to time.

The fix for this is to have both a relay and an aquastat in series to operate the fan. This way the fan will not just operate when the fan relay pulls in and blow cold air while the boiler goes thru the sequence of operation that might include thermostat call for heat to a Zone Valve to end switch to boiler pre-purge to trial for ignition to main burner to water temperature increase to minimum temperature for warm air top be delivered can take up to 4 or 5 minutes of blowing cold air before heat is delivered top the ductwork.

did you follow that? If not read it 3 more times slowly

An aquastat only design may cause the problem you are having. So check if you have both an aquastat and a fan relay in your aftermarket control design. I had fan coils in one of my homes and have tested different control strategies for these type systems.

Mr.Ed

ajbeckerhead

HI Mr.Ed

Thanks for the reply. I understood exactly. I KNOW there is no aqua-stat on the hydronic coil. I had asked about it when the fellow installed the A/C and he wasn't very helpful. I should not have used the installer I used but that is history now. I am glad you replied because I was going to seek information here about just that issue. I had spoken to Braeburn a while back and the techs had alluded to possibly a new feature on their thermostats being able to add a Fan delay as a setting. Unfortunately, it wasn't built in. I understand the need of a thermostat on the hydronic supply and was looking into it to add myself. I couldn't find any thermostatic controls that would close on rise of temp and works on low voltage.
Are you aware of such an item? I would appreciate the help to purchase it. The other issue is if I wire that thermostat between the air handler and the thermostat (yellow wire - fan control) what happens in the A/C season. It would seem I would have to bypass the aqua-stat so the thermostat could send the signal to the air handler fan.

The actual problem I posted with the fan coming on randomly has so far NOT occurred but once this year. I still think there is an issue with the thermostat but like I said in my post I don't want to throw money at it and not repair the problem. Can you enlighten me to what the control board does inside the air handler? I know there is a setup for adding electric heaters. Is it responsible for setting fan speed?

Again, thanks for the reply. I do appreciate your comments and knowledge

EdTheHeaterMan

I couldn't find any thermostatic controls that would close on rise of temp and works on low voltage.

This control can strap on to a pipe (i use the return) close to the fan coil. There is a set of NO contacts that will make on temperature rise. You can use it to make and break line voltage or low voltage.
https://www.supplyhouse.com/Resideo-L6006C1018-High-or-Low-Limit-Circulator-Strap-On-Aquastat-65-200-DegreeF-range-5-30-DegreeF-Adj-Differential?_br_psugg_q=l6006c1018

EdTheHeaterMan

Can you enlighten me to what the control board does inside the air handler? I know there is a setup for adding electric heaters. Is it responsible for setting fan speed?

Here is the wiring diagram from a typical Rheem air hander.
When the control board in the Rheem air handler gets the thermostat signal that closes R to G, the fan will operate. that board may or may not have a short delay on, or, delay off, or, both. The fact of the matter is that the original installer selects the fan speed at the time of commissioning the system.

In the Red circle the Black wire from the motor is Hi Speed, the Red wire is low speed and the Yellow wire is the 208V speed. The factory default is the black wire. No other speed is connected because the unused wires are placed on blank lug terminals on the board.

Rheem has several air handlers including one that has a fan coil built in. Unless I know what air handler you have, I can only speculate what is inside it.

ajbeckerhead

Thank you, Mr. Young. I am an idiot because I had seen controls similar but understood them only to be a high limit - in which that was no good to me. I guess I didn't read well enough. I also referred to the yellow wire in my previous writing by mistake. Anyway, this is a big help to me.
From my previous question: My A/C is also used as a heat pump The thermostat is setup in 2 stage configuration. If I send the green wire from the thermostat to the hydronic control that would be an issue.

I appreciate you helping me with this. It would be nice to be able to have you to speak with when needed I would be glad to compensate you for your time. I would like to have someone I can speak to when there are things I don't understand or when I have similar issues. I will also soon be embarking on putting in radiant floor heat so having an experienced voice would be very helpful Not sure if you would be interested but let me know if you are.

thanks very much again for your help!
Andrew Becker

EdTheHeaterMan

@ajbeckerhead, I am looking at the Braeburn thermostat manual. and I believe you need to set it up in the Installer setup mode to something a little different that what you might think. On installed setup item 11 select [HE EMER]. and on item 13 select [HE AUX].

Call me with quetions

EdTheHeaterMan

OK this is the easiest place to post this wiring diagram (See attached file).

For the most part this is how your heat pump system should be connected by any competent installer. All except the 3 parts in the shaded box and perforated low voltage wires. Those three components are to “Fool" the ECM motor controlled in the air handler to act as if there is an electric resistance heater kit connected but wit for the hydronic coil to be hot. The end result is that when the heat pump is heating, the blower will operate at the appropriate speed for heating. When the Hydronic coil operates the fan should slow down to a minimum speed or stop while the boiler heats the water and then has hot enough water to ensure that cold air will not blow through the ductwork for the time it takes to wait for the duct coil to get hot. By setting the thermostat for Fossil Fuel backup (auxiliary) heat the compressor should shut off and therefore have no heat source for the few minutes it takes to get the hot water from the cold start boiler, into the duct coil. This time lag will result in uncomfortable operation without the additional 3 components L6006C strap on relay, Heat Relay and Heating Fan relay.

Since your duct coil is connected after the blower motor and refrigerant coil, you can use the SetUp in the thermostat to operate as a regular heat pump with electric aux. heat. Or you may SetUp in the thermostat as a Fossil Fuel aux. Heat. I would experiment with both operations to see which one offers more comfort.

The logic or sequence of operations of the additional components are as follows:
1. Call for hear from thermostat for stage one heat pump only
2. Normal fan reversing valve and compressor operation
3. On a call for stage 2 AUX. (W1 AUX on thermostat) heat from thermostat W1 the heat relay will energize
4. This will send 24 volts to the L6006c aquastat.
5. It will open the circuit from thermostat to G on the air handler G. to allow the fan to slow down and or stop completely.
6. This will also send a signal to operate the boiler or hydronic zone valve to get hot water to the coil
7. Within a few minutes or less the water in the coil will be hot and the Aquastat will close a set of contacts to allow 24 volts to operate the Heating Fan Relay
8. Then the heating fan relay closes which will send 24 V power to the W1 and the G terminals on the air handler to simulate a call for heat from the electric resistance kit (which is not there)
9. Once the AUX heat is satisfied the system reverts back to normal heat pump operation as above in step #1 above.

Please note that the G wire from the thermostat must be removed from the air handler and placed on the NC contact on the Heat relay. The COM for that set of contacts on the heat relay must be connected to the G on the air handler.

The relays are available from Granger online. I believe the L6006C is also available there and at Supplyhouse.com. Recommend you get the mounting base for both relays. ALSO you might want to add a fuse to the transformer R terminal inside the air handler to protect you from mis-wiring
This will keep the factory installed smoke inside the transformer.

SuperTech

I've seen similar issues with hydro air setups where the heating fan relay has failed.  I'm not a big fan of the strap on aquastat setups, I've seen too many issues with them. A lot of times the simplest solution is to switch the thermostat from gas/oil to electric.  This is usually done with a switch on the thermostat or in the thermostats configuration settings.  Then the same fan relay will be energized during a calln nndelay relay is needed to prevent the system from blowing cool air in the first minute of the heating call.

EdTheHeaterMan

SuperTech said:

I've seen similar issues with hydro air setups where the heating fan relay has failed.  I'm not a big fan of the strap on aquastat setups, I've seen too many issues with them. A lot of times the simplest solution is to switch the thermostat from gas/oil to electric.  This is usually done with a switch on the thermostat or in the thermostats configuration settings.  Then the same fan relay will be energized during a calln nndelay relay is needed to prevent the system from blowing cool air in the first minute of the heating call.

I agree to a point. The delay may be OK for some but may be a problem for others. The coil temperature is the best solution for this application. You see This is not just a case of using a strap on aquastat to operate the heating speed of a PSC motor. This is an ECM motor situation. You can not just break the line voltage to the motor or any of the communication wiring. The strap on aquastat prevents the G wire from being energized on a call for hydronic heat until the return line of the heating coil is at least 145°. Once that milestone is accomplished, the fan can operate but on the ECM motor it will operate at 15% to 25% speed if there is no call for heat to the circuit board of the air handler.

Before ECM controllers this was an easy job. Now you need to fool the controller to get the fan speed up to the necessary CFM to heat the structure. 200° boiler water with only 20% CFM from the ECM motor is the problem that @ajbeckerhead currently has. This will do the trick with Legacy heat pump wiring from the thermostat he selected for use (or which is existing) to the ECM Air handler he has. We are solving the two problems he has experienced with the current professionally installed system. Those two problems are blowing cold air until the boiler water temperature is hot enough in the duct coil, and the low speed of using only the G terminal to operate the fan with no other call for cooling or heating (which is required to get past the very low CFM setting of energizing the G terminal only)

I believe you will see the logic of the Sequence of Operation to my control design if you look closely and read the description above.


As far as your experience with problematic operation with a strap on aquastats I'm assuming that “getting the temperature setting just right” has been the issue. I have experienced that issue and have designed a series circuit to bring on the fan motor speed with both a temperature set of contacts, and a call for heat relay set of contacts. The motor won’t start until the coil is hot and the motor will turn off as soon as the call for heat has ended. This eliminates the “getting it just right” temperature setting of the aquastat only approach.

With AJ Becker's set up using the heat pump, there is another issue of blowing cold air when the system switches from compressor heating mode to AUX heating mode. The time delay from compressor off to coil hot can be as much as 6 minutes in some cases. Consider a cold Taco 570 zone valve gets a call for heat from the AUX (W1) thermostat contacts, and takes 90 seconds to energize the end switch to turn on a cold start boiler. Then the boiler now takes a pre purge and ignition cycle before the main burner ignites, then the water in the boiler takes another 2 to 3 minutes before it gets warm enough to heat the coil in the ductwork. With only setting the thermostat to Oil Gas so the compressor does not run, you will not get the two stage heat pump operation. If you set the thermostat to a heat pump with fossil fuel backup the compressor will stop heating and there can be as long as 5 minutes of cold air blowing while the coil takes its good ‘ole time to get hot.

Again this control setup has been well thought out over the past few months in order to get an ECM equipped air handler to operate comfortably with hydronic duct coil heating as the back-up or AUX heating for heating needs below the Heat pump break even point. My son had an ECM air handler and a HydroDuctCoil system with multiple zones for AC and heating that also incorporates radiant floor heat with the duct system to take up the slack when the outdoor temperature is too low for the radiant floor to keep up with the demand. I have tried several different approaches to solve this, that is how I know the aquastat can not break any of the line voltage or communication wires to the ECM motor to keep the fan from operating. This way will work! I stake my reputation on it!

Mr. ED