Service & Maintenance / Extra Edition / HVAC Light Commercial Market / Rooftop Units

Troubleshooting Challenge: A Rooftop Unit That Won't Shut Down

Figure 1. (Click on the image for an enlarged view.)

In this month’s troubleshooting situation, our customer has called to say that the older package unit that heats and cools his office is managing to warm up the area, but then seems to cool down too much before providing heat again. When you arrive, the first thing you note is that the indoor blower motor is operating, and that the fan switch on the thermostat assembly is set in the position shown in the diagram in Figure 1.

You also note that:

• The discharge air temperature is what you would expect it to be for this gas-fired heating system.

• Turning the thermostat to a lower set point and waiting a reasonable time proves that the indoor blower motor doesn’t shut down.

When you access the unit’s electrical system, you note that the burners are operating normally since the thermostat is again calling for heat, and you begin your troubleshooting procedure by placing a voltmeter at H1 and H2 on the IBDR coil and confirm 24 vac. When you instruct the customer to turn the thermostat down to a lower set point, you note that the burners shut down, and after a delay, your voltage reading at IBDR is 0 vac, while the indoor blower motor continues to operate. Your next voltage test is at #2 and #4, M1 and M2, and your reading is 0 vac.

Your troubleshooting question: What is your next step in solving this problem?

Compare your answer with ours by clicking on the PDF link below.

For information on Jim Johnson’s training DVDs for troubleshooting HVACR electrical circuits, click here.

Publication date: 03/07/2011

Links

Did you enjoy this article? Click here to subscribe to The NEWS Magazine

Recent Articles by Jim Johnson

You must login or register in order to post a comment.

Multimedia

Videos

Image Galleries

2015 ACCA Conference

Images from the 2015 ACCA Conference in Grapevine, Texas. Posted on April 8, 2015.

Podcasts

NEWSMakers: Clint Schreck

Clint Schreck, general manager, Columbus Worthington Air, Columbus, Ohio, discusses winning Angie’s List Super Service Award, how to handle online reviews, and much more.

More Podcasts

ACHRNEWS

NEWS 05-25-15 cover

2015 May 25

Check out the weekly edition of The NEWS today!

Table Of Contents Subscribe

Legislation and Regulation

What legislative/regulatory issue is most important to you as a HVAC business owner?
View Results Poll Archive

HVACR INDUSTRY STORE

2015.jpg
2015 National Plumbing & HVAC Estimator

Every plumbing and HVAC estimator can use the cost estimates in this practical manual!

More Products

Clear Seas Research

 

Clear Seas ResearchWith access to over one million professionals and more than 60 industry-specific publications, Clear Seas Research offers relevant insights from those who know your industry best. Let us customize a market research solution that exceeds your marketing goals.

DON'T MISS A THING

Magazine image
 
Register today for complete access to ACHRNews.com. Get full access to the latest features, Extra Edition, and more.

STAY CONNECTED

facebook icontwitter iconyoutube iconLinkedIn i con