On a Trane RTEM economizer module, 8 flashes means a problem with the mixed air temperature sensor. If the unit has only a motorized damper and no mechanical linkage between the return and outdoor dampers, Trane says to ignore the code. Otherwise, unplug the sensor and measure across two pins. An open or a short means replace the sensor.
What the RTEM LED reports
The RTEM reports its state and its faults on an LED. Trane’s article “What are the Economizer fault codes” gives the following pattern:
- Off: no power, or a failure.
- On: normal, OK to economize.
- Slow flash: normal, not OK to economize.
- Fast flash: communications failure.
- 1 flash: actuator fault.
- 2 flashes: CO2 sensor.
- 3 flashes: return air (RA) humidity.
- 4 flashes: RA temperature.
- 5 flashes: outdoor air (OA) quality.
- 6 flashes: OA humidity.
- 7 flashes: OA temperature.
- 8 flashes: mixed air (MA) temperature.
- 9 flashes: RAM.
- 10 flashes: ROM.
- 11 flashes: EEPROM.
Two points are easy to miss. First, a slow flash is not a fault. Trane lists it as normal operation in which the module is not OK to economize. It is not listed as a fault. Second, the numbered flashes 2 through 8 each name an input. A flash count in that range points to the sensor it names. It does not by itself prove that the sensor is bad, because the wiring and connection to that sensor are part of the same input.
A note on Trane’s own pages. Trane’s separate LED codes article for light commercial units lists a shorter set of RTEM codes than the economizer fault codes article above. The two pages also word some codes differently. For example, the LED codes page words 7 flashes as no communication with the RTRM or a failed outdoor air temperature sensor, and groups 9 through 11 flashes as an internal fault. We follow the economizer article here. Check your unit’s service literature if the two do not agree.
Actuator fault or communications failure
The LED pattern separates two faults that are easy to confuse. One flash is an actuator fault. A fast flash is a communications failure. The first is a fault with the actuator. The second is a communications failure. We have only the LED pattern for these two. We do not have Trane’s diagnostic steps for either, so we do not offer any. If you see one of them, use Trane’s service literature for your unit.
The 8-flash: mixed air temperature sensor
Trane’s article “Why am I getting an 8 flash code on my economizer” covers this one. Eight flashes is a mixed air temperature sensor problem. Trane gives two branches:
- No economizer linkage. If the unit has no mechanical linkage between the return and outdoor dampers, meaning it has a motorized damper only and no economizer, ignore the code.
- Economizer with linkage. Confirm the mixed air temperature sensor is connected to the MAT inputs on the RTEM, then unplug it and measure across two pins. If the reading is open or shorted, replace the sensor.
Because Trane’s first branch is whether the unit has an economizer at all, settle that from the unit’s documentation before you spend time testing a sensor. A code that Trane says to ignore on a motorized-damper-only unit is not a reason to replace anything. If the unit does have the economizer linkage, the sensor test below is the next step, and it is quick.
The test checks for an open or a short and nothing else. We do not give resistance values, a temperature-to-resistance chart, or a pass range, because the source does not give them and a sensor that reads in range is not covered by the guidance we have.
How to test the mixed air sensor
- Confirm the code and the module. You should see 8 flashes on the RTEM of a Trane unit. This guidance is for that module.
- Decide whether the code applies. If the unit has only a motorized damper, with no mechanical linkage between the return and outdoor dampers, Trane says to ignore it.
- Isolate the unit. Remove power and apply your site’s lockout/tagout. Damper actuators move, so keep hands clear of the damper linkage.
- Find the sensor and its connector. Confirm the mixed air temperature sensor is wired to the MAT inputs on the RTEM.
- Unplug the sensor, as Trane directs.
- Measure across two pins. Use a meter to measure resistance across the sensor’s two pins.
- Read the result. An open or a short means replace the sensor, per Trane. The source we used gives no further instruction for a sensor that reads neither, so check the wiring and connections and then Trane’s literature for your unit.
- Reseat the connector and restore power. Watch the LED to confirm that the 8-flash has cleared.
- Order only after you have the sensor’s part number, from the failed sensor or your unit’s parts documentation.
Parts involved
Most RTEM-related parts are not matched to a listing in our catalog. The table says so rather than implying a fit, and we do not claim fit to any specific Trane unit.
| Component | Role in this issue | Where to find it |
|---|---|---|
| RTEM economizer module | Reports the codes above. Not matched to a listing; send the number from the module. | Request a quote |
| Mixed air temperature sensor | The subject of the 8-flash. Not matched to a listing; send the number from the sensor. | Contact us |
| Damper actuator | 1 flash is an actuator fault. Not matched to a listing; send the number from the actuator. | Request a quote |
| CO2, humidity and temperature sensors | Flash counts 2 through 7 name these inputs. Controls and sensors are listed under several brands; none is matched to an RTEM input, so search by the number on your sensor. | Controls |
| Other Trane items | Trane-brand parts we list. | Trane Replacement Parts |
Scope: This article covers the Trane RTEM economizer LED codes and the 8-flash mixed air sensor guidance as described in the Trane support articles under Sources. It does not apply to other manufacturers’ economizers, whose codes and tests differ. Check your unit’s own service literature for anything not covered here.
Before you order
Confirm your unit’s exact model and serial number from its nameplate before ordering. Search the part number in our site search, or browse the Trane replacement parts collection. If the number you need is not listed, use our request a quote page, or contact us at help@totalhvacparts.com and we will help confirm fit. Our guide to finding the correct replacement part from the model and serial number covers where to look. For other Trane rooftop codes, see the articles on ignition board flash codes and the RTRM 2-flash code.
Frequently Asked Questions
What does 8 flash mean on a Trane economizer?
Eight flashes on the Trane economizer module means a problem with the mixed air temperature sensor (Trane support article on the 8 flash code). If the unit has only a motorized damper and no economizer linkage, Trane says to ignore the code.
How do I test a Trane mixed air sensor?
Confirm the sensor is on the RTEM’s MAT inputs, unplug it, and measure across two pins. Per Trane, an open or a short means replace the sensor. We do not publish resistance values because our source does not give them.
What does a slow flash mean on a Trane economizer?
Trane lists a slow flash as normal but not OK to economize. It is not a fault code. The module is reporting normal operation without permission to economize.
What is the difference between a 1 flash and a fast flash on a Trane RTEM?
One flash is an actuator fault. A fast flash is a communications failure. Those are the two LED patterns Trane lists. We do not have Trane’s diagnostic steps for either, so use Trane’s service literature for your unit.
Sources
- Trane support, “What are the Economizer fault codes” (RTEM LED pattern, flash counts 1 through 11)
- Trane support, “Why am I getting an 8 flash code on my economizer” (mixed air sensor guidance)
- Trane support, “List of Light Commercial LED Codes” (shorter RTEM set)
Economizer work involves energized control wiring, line-voltage components in the unit, and moving dampers and actuators. Service should be performed only by qualified personnel, following Trane’s service literature for your unit and your facility’s lockout/tagout procedures.