Honeywell TR21-H/U NTC Non-Linear Temperature/Humidity Wall Module. The TR21, TR22, are a family of direct wired wall modules for use with Honeywell Excel 600, 500, 100, and 80 controllers; Excel 10 W7750, W7751A, W7752, and W7753 controllers; W7761 Controller; and Spyder Unitary Controllers.
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