Mechanical Equipment FAQs
Below is a list of common questions and answers about Frees Inc. and our solutions. Please take a moment and see if your questions can be answered here. If not Please contact at 1-800-978-3733.
Q: I turned the RAU (Replacement Air Unit) on at the panel and it never did anything.
A: There are really only two things that can prevent the unit from energizing the blower if it has been off and just turned on. If the overloads on the starter inside the unit control panel have tripped, there is never a signal going to the discharge damper to tell it to open. Reset the overload and the problem will go away but the reason the overloads were tripped should be determined and remedied. The other thing that can prevent the fan from coming on is the discharge damper. If the damper gets power from the overloads on the starter then it should start stroking open. The damper actuator has an internal end switch that closes when the damper has stroked enough for the unit to come on. If it is determined that there is power to the damper actuator, either the actuator is bad or the end switch is never being made. Physical observation of the damper to see if it is actually stroking will determine whether it is the actuator or the actuator end switch.
Q: The RAU came on the flame failure light is on, but it won’t heat.
A: If the unit attempts to light and either truly does not light or lit but can’t sense that it lit, and then it will lock itself out and turn on the flame failure light. This is a safety control and requires a visit to the unit mounted control panel to reset it. The ignition control module (about 5”X5” and either Grey or Red depending on the model) has a reset button on the face of the cover that will need to be pressed. If the unit trips the flame failure again other problems need to be diagnosed.
Q: The RAU came on, the flame failure light is not on, but it won’t heat.
A: There are several safety devices upstream of the ignition controller. If the blower is on then the damper has opened and given a signal to the motor starter to energize the blower fan. The safety devices that are between the damper motor and the ignition controller are, airflow switch (some models have two), high temperature limit switch, low gas pressure switch, and high gas pressure switch (only if burner is over 1 million BTU). The most likely device is the airflow switch. This device detects a pressure differential between the upstream side of the burner and the fan inlet. There is pressure sensing tubes that could be loose, cracked, or stopped up by insects. Dirty filters upstream could impede the airflow. The profile dampers (both sides of burner) could be adjusted incorrectly. The belts could be loose enough that the fan is not spinning at its proper speed. Discharge damper motor could have stroked but not actually opened the damper. The high temperature limit switch most likely is not the problem. It only trips when the temperature inside the unit cabinet has exceeded the set point which is usually set about 180 degrees. If this device is tripped there was probably a fire in the unit or the device has failed. The low gas pressure switch trips when the incoming gas pressure drops below the set point. If the gas has been turned off for any reason and the line pressure drops this device will trip and has to be manually reset when gas pressure is restored. The high gas pressure switch trips if the burner manifold pressure exceeds the set point. This rarely trips and if it does the actual gas pressure needs to be calibrated.
Q: The RAU came on and the heat came on but the air won’t get warm enough.
A: The air temperature is controlled to a set point on the remote panel. There is a temperature sensor mounted somewhere in the duct relatively close to the unit. This sensor is a thermistor that sends a resistance signal to the other devices in the unit. If the sensor gets wet it shorts out the terminals and the resistance signal that is sent tells the other devices that it is hot and the burner throttles down to low fire. Water will not damage the sensor but will cause it to send an incorrect signal. Finding the sensor, removing it, and drying it out will cure the problem. The cause of why the sensor got wet will also need to be corrected or it will happen again the next time it gets wet.
Q: The RAU came on and the heat came on like normal but after about 3-5 minutes both the heat and the fan went off.
A: There is a device that is sometimes labeled “Low Limit” or “Freeze Stat”. What this device does is turn the blower off if the heat does not come on to prevent blowing cold air into the building and freezing things like sprinklers. The way it works is that when the unit is asked to come on a timer starts timing. There is a temperature sensor inside the blower cabinet downstream of the burner. When the temperature sensor warms up to its set point (usually 38-40 degrees) it stops the timer from timing. If the sensor does not warm up and the timer times out, a relay is energized and de-energizes the blower. The unit will stay latched in this mode until the unit is turned off and back on which unlatches the relay. If the heat truly is coming on and the temperature set point and the time (usually 4-5 minutes) are correct, the device is probably defective. There are two styles of these devices. The newer models have solid-state devices and if they are not working properly they will need to be replaced. The older units have a pair of devices, a thermostat and a timer. If this fails it is usually because the copper capillary tube has rubbed on something, developed a leak and failed. On this style the thermostat only needs to be replaced and not necessarily the timer.
Q: The RAU will come on and the heat comes on but the heat (light) goes on and off every few seconds and never heats up like it should.
A: This is usually indicative of an airflow switch that is “Chattering”. The airflow switch either needs to be adjusted or the cause of insufficient airflow needs to be determined.
Q: The RAU will come on the heat works fine until the temperature gets down to about 25-30 degrees then it goes off.
A: This indicates that the airflow switch needs to be calibrated. The air temperature affects the air density. When the air is cold it is dense and the airflow switch can close. When the burner lights the temperature sensor is cold and when the burner lights it immediately goes to high fire. This sudden burst of hot air lowers the density and the airflow switch opens. This de-energizes the burner; the air gets cold, the airflow switch closes, and the entire lighting process will repeat. A minor adjustment to the airflow switch will eliminate this problem.
Q: The RAU has lights on the panel at the unit itself but some of them are not lit up while the unit is running.
A: Most units installed by Frees Inc. have annunciation lights inside the unit mounted control panel. These lights are normally (not necessarily all models), power, damper, low limit, blower, airflow, high limit, low gas, high gas, burner, and flame failure. These lights are in the exact order that the control power goes from device to device through the unit. If the unit has problems such as no blower, or not heat, the first light that is NOT lit is where the control power stopped and indicates where to look for the failure. If the unit is in the summer mode there will be no lights lit below the airflow light.