Chamber Failing To Heat Or Cool? Is your Limit Controller set to your testing needs?

If your chamber is failing to Heat or Cool, please use the following FAQ, Troubleshooting Guide to help you.

Before carrying out any changes on your limit controller, please refer to your Sales Acknowledgement for specific information regarding your chamber’s capabilities. If you need a copy of this, please contact support. 

This is important as each chamber is calibrated to work at different ranges. Please never exceed or tamper with your chamber’s range.


                                                Watlow PM                  Love Controller 


What is a limit controller?                                                                                   

Limit controllers are meant to provide power cut-out to protect employees and products being tested as well as machinery against temperatures that are too high or low. Power cut out would occur at the temperature set by the end user on the limit controller. A technician can view the limit controller as “Big Brother” or as a redundant safety in your testing in the event there is a main controller failure. The Limit Controller has the final say in whether or not a chamber will power up past a certain setpoint entered by the end user.


How should my limit controller be set?

This would depend on the absolute maximum safe temperature your product being tested can safely be heated or cooled to (not the temperatures a product will be tested at) for example, a product being tested in an AES environmental test chamber might need to be tested at 210c, but, the product absolutely cannot exceed 240c for risk of product damage or thermal event. This would mean setting the limit controller to 240c so in the event there is a malfunction with the main controller temperature regulation, or, there is a mechanical failure and the temperatures go beyond safe limits, the limit controller will step in and cut power to the chamber and shut it down. Now this would be the maximum temperature that a product can safely handle, not the temperature you would be testing at which would have to be lower than the maximum safe limits you would enter into the limit controller. The same can be said for low temperatures. However, this only applies to certain chamber models that are equipped with a Watlow EZ-Zone Limit controller pictured above on the left.


Why won’t my chamber heat or cool past a certain temperature? 

On our stock chambers the limit controllers are set close to the upper and lower limits. 

Oftentimes, an incorrectly set limit controller (verified by pressing SET button one time on LOVE controllers) can be what prevents a chamber from reaching the desired hot or cold setpoint. It is one of the easier checks when your heating or cooling functionality is suspect. Limit controllers are installed with safety in mind. A limit controller's job is to prevent over or under temperature conditions.


Example of an incorrectly set limit controller  

A simple example of a limit controller that is set incorrectly could be the following scenario: An employee uses the limit controller in their testing and has set it to a temperature that is lower than your test heating requirements. A sign of this would be that regardless of where the main controller is set, the heat is not increasing. This is typically a sign that the limit controller is set too low. 


How do I set my Limit Controller? 

Love Controller (Heat only)

You can set the limit controller by pressing the set button which will display the current High Limit Setpoint and using the arrow keys to enter the maximum temperature your testing can safely be tested.


WATLOW PM (High Low)

Changing the Set Point

From the Home Page the “Limit Set Points”, high and low, can be changed. Pushing the infinity key one time and the Low Limit Set Point LL.51 prompt will appear in the lower display while the current set point will be displayed above. Pushing the Up or Down  keys will change the set point. Once done, simply push the Infinity Key ∞ to display the High Limit Set Point Lh.51 will appear below and the current High Limit Set Point will be displayed above. 


Please see below for detailed instructions on how to set your controller's temperature units from C to F (& Vice Versa). Please be very careful to follow the instructions very carefully, as to not change any of the other settings.

Watlow EZ-Zone Temperature Change Instructions 

Love Limit Controller Temperature Change Instructions 


If you have any questions regarding your chamber’s specific set points, please refer to your sales order or reach out to support.