Lec T663AW PTC replacement - correct resistance?

[Roy22]

I'm trying to fix an old fridge/freezer about which I can find hardly any technical info. It's a Lec T663AW with a ZEM HQY90AA compressor, rated at 1/6HP. The 4uF run capacitor is OK, also the windings (22/25ohm) and the overload too. It doesn't have a proper relay as such, just a PTC. On opening that unit, parts of the silver disc PTC fell out. The plastic exterior shows slight signs of overheating. I've no idea if the unit's exterior markings ARB2 7100D4 meaning anything.

My hope is that, with a new PTC unit, it might be fixable. I've found a visually identical unit, currently on its way (via the slow boat from China), though I cannot know the PTC's suitability to my fridge.

The old/broken PTC unit, of which three quarters of the silver disc remains intact and in place, gives a 8.4 ohm resistance. My assumption is that the missing quarter would have reduced the resistance to a lower figure. I have found general comments suggesting 3 to 6 ohms is common, but having also found a Chinese supplier of these silver discs, I have seen values from 4.7ohms to several tens of ohms. Not so clear then.

My assumption would have been that a fairly small fridge/compressor would have needed less starter current, and so a higher PTC resistance. But the existing 8.4 ohms of the three quarters intact one is making me look towards the 4.7 ohm one.

Can anyone offer any advice on, in the absence of detailed tech info, what value PTC it might need? I don't want the thing to quietly overheat if I do get it running again.

[redroge]

Have you tried Parts Center they may have something suitable

[Roy22]

Have you tried Parts Center they may have something suitable

Yes I have, it seems to fall under a large range of rarer parts all quoted as '4-5 weeks' delivery. Which is rather a depressingly long/blanket statement. I will ask further though.

I've spent a little more time on the problem, having found a wiring diagram, and am quite puzzled. The single clunk at switch-on is coming from the solenoid valve, not the compressor as first assumed. The solenoid activation clunk (looking at wiring diagram) means the fridge thermostat is correctly calling for cooling; that comes from the output of the Freezer thermostat, likewise correctly calling for cooling. So the live feed goes via the two thermostats and down to the compressor, where it passes through the Overload Protector (nice low resistance so OK). The Neutral feed from plug through run capacitor (checked & also substituted) thence to the PTC Relay assembly is intact. So seemingly the mains power is reaching the silent compressor OK.

Measuring the current draw at the plug, it's just 0.07 amps. Meanwhile the compressor windings are intact (22.5/17.8, total 40.0 vs theoretical 40.3 ohms, so OK I think).

Even if the motor was seized or the PTC to blame for not starting it, with intact windings I would expect a heavy current draw at switch-on, maybe some humming, and the Overload device to cut out/in every few seconds. Instead we get a tiny current draw, probably down to the solenoid and a heater (somewhere) drawn in the diagram, otherwise silence and trivial total current draw. How is this possible?

[seanf]

What voltages are you getting at the compressor pins?
Could you have an open neutral?