DIY Home Projects: Diagnose HVAC Problems

by Fred Fauth on April 19, 2013

This is an article from contributing writer, Fred Fauth from One Project Closer. Check out some of his other contributions to One Smart Dollar, like the cost of international adoption and DIY Drywall Repair.

A Homeowners Checklist for HVAC Problems

Most heating, ventilation and air conditioning (HVAC) problems are beyond the capabilities of homeowners. Even with the right know-how, the necessary tools and equipment are prohibitively expensive. I guess that’s why home warranties are such an attractive option. Despite all that, there are a few things homeowners can do when their HVAC is on the fritz. Here’s a short checklist to run through which may eliminate the need to schedule a service technician.

Check Your Air Filter

The best (and easiest) thing homeowners can do is regularly change their HVAC system air filter. This simple step can help ensure functionality and extend the life of an HVAC unit. Dirty filters restrict air flow, causing the unit to work much harder for the same results, and that can lead to all sorts of problems. For instance, pictured below is an indoor evaporator coil that has frozen over because the air filter was too dirty.

HVAC professionals I’ve spoken with say that a standard, 30-day air filter is sufficient for most units. If allergies are a problem, consider upgrading to pleated, allergen furnace filters. Anytime you’re doing something that creates a lot of dust, like home renovations involving drywall sanding, change the filter 24 hours after the work is complete and the dust settles.


Check the Fuse

Blown fuses are another inexpensive, albeit less common, solution to a malfunctioning HVAC unit. The outdoor compressor unit will have a dedicated fuse which can go bad over time. Much more likely, the fuse served its purpose, protecting components when the current exceeded safe levels.

Visually inspect the fuse(s), looking for flash marks in and around the window. If you have a multimeter, set it to Ohms, and check for continuity of the fuse and fuse box. If the fuse is bad, you can usually find replacements for about $15. Here’s a good article about testing and replacing HVAC fuses.


Air Temperature Change

The temperature at the evaporator coil and the air supply should differ by 18° – 20°. Homeowners can easily check the temperature differential by inserting a digital cooking thermometer just after the coil and just before the filter. If the temperature change is lower that may indicate a dirty coil, which can be cleaned with careful vacuuming.


Inspect and Clean the Drain Line

Sometimes the drain line can become clogged, especially during the winter (when the drain isn’t very active). This can lead to water buildup, and eventually the condensation pan and coil will rust. Most drain lines feature a removable cap. Run 1/2 cup of bleach through the drain line annually, and check that the pump is working properly.


One Project Closer is a home improvement site where you’ll find expert how-to guides called Pro-Follows. Every Pro-Follow is the result of shadowing a real contractor on an actual job site. In addition, OPC provides tool reviews and coupon information for DIY superstores like these Lowe’s discounts. If you enjoy home improvement, check out One Project Closer.

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Fred Fauth

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  • Thanks for the info. HVAC is one thing that I won’t touch. I am pretty hands on, but I know those tools are very expensive and I don’t have the know-how.

    • Yeah I definitely won’t touch HVAC

    • All of these things are pretty easy checks with no real “HVAC” work – definitely worth doing these even if you are more comfortable calling a professional. This will help them diagnose the problems more quickly, and may save you a $100 service call.

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