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Phil, Mechanical Engineer
Category: Home Improvement
Satisfied Customers: 8517
Experience:  Retired contractor, 51 years experience
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ComfortLink II won't start cooler. "Err 91". How do I

Customer Question

ComfortLink II won't start cooler. "Err 91". How do I resolve this?
Submitted: 1 year ago.
Category: Home Improvement
Expert:  Phil replied 1 year ago.

Hello, this is one of the most complex and difficult to diagnose error codes to determine and repair.

If you want to tackle this yourself I need to know a lot about your electronics skill sets and experience with this type of equipment.

We can go from there.

Customer: replied 1 year ago.
Hi, thanks for replying. I hope to do some basic checks first before taking up your time. I am a first-time homeowner and inherited this aircon system from the previous occupant. I have zero electronics experience, but figured out how to start the lawn mower and weed whacker by following the manual, so hopefully the same approach can be applied here lol.The manual says Error 91 means it has communication issues. Are there any basic checks I can perform? There is some sort of central unit in the attic which I tried turning off and on. There is what I think is a refrigerant unit outside the house, but I can't figure out how to turn it on. Or should I try tracing the wires from the ComfortLink console, and see if they are connected properly?
Expert:  Phil replied 1 year ago.

Hello again, those controls are complex enough that only about 2 HVAC techs in 10 would be able sort the problem out efficiently... the other 8 could not. The odds that you can get lucky and attain an effective fix are in the 1 in several hundred range.

The odds that you can hurt yourself of the unit by trying are in the 50% range.

You can however try tracing the wires and looking for bad connections, and then replug all of the connections in the unit (with the power off) that would burnish them all, its safe and you would have about a 10% chance that this would fix the problem.