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Tech Forum

June 2012

Compressor Starter

I am looking for a positive temperature coefficient motor starter for a compressor. Or, I need help using different parts such as a single pole contactor/relay for a hard start. The part I want to replace has the following number: RF-6850-18, and consists of a PTC starter and an overload protector. Can I replace this with a hard starter contacter? I can photocopy the schematics and email anyone who can help me.

Michael Farley
Cincinnati, OH


The original part is shown at www.repairclinic.com/PartDetail/Start-Device/RF685018/1569121.

The three terminals on the device are C, S, and R. C is connected to the COMMON of the compressor, with S being START winding, and R being RUN winding.

I'd suggest replacing the original device, and adding the proper MARS hard start device to kick the compressor. You don't want to bypass the overload! PERIOD!

MARS Motors & Armatures, Inc.,  has hard start devices and torque multipliers for refrigeration/AC compressors. I've used a smaller MARS hard start device on several refrigerators, and they work fine. (www.marsm-a.com/CGI-BIN/LANSAWEB?WEBEVENT+R06630136135017015394091+ML6+ENG).

I can't find the paperwork on the last MARS device I purchased. Any local HVAC distributor should be able to locate what you need, depending on the compressor size. It's just a two wire hookup.

I'm including a PDF document from MARS and my refrigeration document for you to view.

Larry Kraemer
via email

I work for a major appliance repair company/retailer. Replacing the factory compressor start device with an after-market hard start kit is not recommended. Most of those kits — if not used or sized correctly — can cause permanent compressor failure. I would suggest trying to source the correct part by model and serial number of the refrigerator. There is a major appliance parts dealer in Cincinnati and Dayton that can help. If you can not find a model or serial, I suggest Whirlpool part number 8201786. This kit covers several different compressors, as well as wiring connections.

Sean Battito
Mohnton, PA

I've bought PTC starters for refrigeration compressors from www.repairclinic.com on a few different occasions. A local appliance shop with a parts counter should be able to supply them too, either OEM or a universal replacement. The "hard start" kits you can get are nothing more than a standard PTC starter, overload protector, and capacitor stuffed into a housing. The one time I tried one of those, it failed within a few weeks.

If you want to try rolling your own, this schematic is said to work although I've not personally tried it. Digi-Key, Mouser, and other electronics distributors carry a selection of PTCs and bimetal circuit protectors that could be used.

James Sweet
via email

Go to any well stocked refrigeration supply house and ask for a universal compressor starter.

This will be a device with leads. (I have no idea what's inside.) Connect it as shown on the package, removing the existing starter device.

These things work every time. Be sure to leave any original thermal protective device intact.

They can also be used on small air compressors that use PTC devices as starters.

Don Pomeroy
Manchester, NH