AC troubleshooting


Old 05-29-15, 03:11 PM
Thread Starter
Join Date: May 2015
Location: United States
Posts: 3
Received 0 Votes on 0 Posts
AC troubleshooting

Hoping to get some help identifying the part/parts I need to get my AC going again.

My unit is a Lennox HS29-024-2P single phase, with a non-scroll compressor. Neither the compressor or the fan are kicking on. After checking the thermostat and breaker, I removed the panel on the unit and started poking around with my multimeter. I have power everywhere I should. The contactor is engaging when the thermostat turns on. The start capacitor doesnt look bad at all. The dual capacitor is pretty rusty, but neither appear to be bulging. I also have a potential relay in there, but Im assuming thats functioning properly as well since I was reading 240v at the capacitors. Im guessing that one or both capacitors are bad, but didnt know if there was a way to test them to figure out which one was causing the trouble.

Its a toasty 88 degrees here in the living room, so any help at all would be greatly appreciated!
Sponsored Links
Old 05-29-15, 03:54 PM
Join Date: Aug 2008
Location: Texas, California
Posts: 1,460
Received 0 Votes on 0 Posts
You need a multimeter with capacitance reading.
Old 05-29-15, 07:48 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 52,729
Received 346 Votes on 324 Posts
Welcome to the forums.

I would normally have you check for 240vac on the load or A/C side of the contactor but you said you did measure 240v inside.

It's pretty rare for the compressor and the fan parts of the cap to fail at the same time and even then..... the fan or the compressor usually hums until it cuts out on high heat.

I would change the dual cap but I'm not 100% certain that's the problem.
Make sure all the wires are tight on the caps.

Lennox HS29 manual with wirng diagrams.PDF

Last edited by PJmax; 05-29-15 at 08:05 PM.
Old 05-30-15, 10:28 AM
Thread Starter
Join Date: May 2015
Location: United States
Posts: 3
Received 0 Votes on 0 Posts
Glad I found the site and thanks for the responses.

Turns out the connectors on the rusty dual capacitor had some corrosion as well. I gave each wire a good jiggle, then manually depressed the contactor switch outside and it kicked right on..
Old 05-30-15, 10:39 AM
Bob14525's Avatar
Join Date: Jun 2013
Location: USA
Posts: 1,470
Received 11 Votes on 8 Posts
Turn off the power and clean the connectors well, both the wire ends and the capacitor terminals. If you have poor contact, you have high resistance which generates heat. The terminals could actually burn up. Better to be safe than sorry.
Old 05-30-15, 11:03 AM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 7,372
Received 10 Votes on 8 Posts
I would replace the cap and clean the wire connections to it.
Old 05-31-15, 11:09 AM
Thread Starter
Join Date: May 2015
Location: United States
Posts: 3
Received 0 Votes on 0 Posts
I just replaced the connectors for the wires and cleaned the cap terminals with a wooden handled wire brush.

I found both replacement cap's at General Supplies Inc for quite a bit cheaper than everyone else. Does anyone have anything bad to say about them or their quality, or should I pull the trigger for a good deal?

Lennox 89M73 35/5 MFD 370V Round Dual Capacitor

Packard PRMJ145 145-174 MFD 330V Round Start Capacitor
Old 05-31-15, 02:10 PM
Join Date: May 2008
Location: Wisconsin USA
Posts: 715
Received 0 Votes on 0 Posts
When MFD was correct, I always bought 440 volt capacitors; they replace the lower voltage capacitors. Also, stocked them on my vans with different MFD ratings to meet replacement needs.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes
Ask a Question
Question Title:
Your question will be posted in: