Jon Klima, Owner
360 Trout Lane, PO Box 23, Guffey, CO 80820
Phone: 719 479-2281,  Email:
In business for 40 years







The Solar Age Partner/Hi Square/Hawthorne 4020 is a basic ON/OFF differential temperature controller from the late 1970s and early 1980s. It is used for air space heating systems and provides the basic "ON" and "OFF" differential functions along with an option to use a high limit switch. This controller's output is limited by a 6 amp fuse.


I've tested this controller and its delta Ts are 37º/19º @ a storage temperature of 77 ºF, 43º/21º @ a storage temperature of 126 ºF, and 48º/21º @ a storage temperature of 156ºF.


This 4020 controller uses two readily available standard 10 K ohm thermistor sensors, one for the collector and one for the storage or room.


If you are looking to replace your defective The Solar Age Partner/Hi Square/Hawthorne 4020 controller or just want one as a backup, order this one today as it is the only one left. Prices shown do not include postage.  Colorado sales will be charged the appropriate sales tax. Yes, I accept credit card payments through PayPal, checks, and money orders.  For questions or to place an order, send me an email (see top of this page) stating what you are interested in along with your zip code.  I'll check the postage to your zip code and send you a return email with the total cost.



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This page was last changed on 2-26-2019