How to Tell If Your Heat Pump Is Actually Working: Checks a Homeowner Can Do

A heat pump that’s “not working right” could mean a dozen different things, and half the time the system is actually fine. Before you call anyone, there are a few checks you can do yourself in about 15 minutes that will either put your mind at ease or give you something concrete to tell a tech.

Start with the basics

Check the thermostat first. Make sure it’s set to the right mode, “heat” in winter or “cool” in summer, and that the temperature setpoint is actually calling for the system to run. It sounds obvious, but a surprising number of service calls come down to a mode switch.

Then check your air filter. A clogged filter starves the system of airflow and is the single most common reason a heat pump struggles. If you can’t see light through it when you hold it up, replace it. A dirty filter can cause the system to short-cycle, run constantly, or trip the unit off entirely.

Next, go outside and look at the outdoor unit. In heating mode, the outdoor coil extracts heat from the air, so some frost buildup on the coils during a cold morning is normal. The unit should defrost itself periodically, and a typical defrost cycle runs about 5-15 minutes. What’s not normal: a solid block of ice covering the entire unit, or a defrost cycle that runs for more than 15 minutes with no improvement. That’s a flag.

What “working properly” actually looks like

When a heat pump is operating normally in heating mode:

The air coming from your vents should feel warm, but not hot the way a gas furnace does. Heat pumps run at lower supply temperatures, typically in the range of 90-110°F at the vents versus roughly 120-140°F for gas. This surprises a lot of Bay Area homeowners who switch from gas. If the air feels lukewarm and your house is still getting to setpoint, the system is working.

The outdoor unit runs in long cycles rather than short bursts. A heat pump is designed to run steadily. If it’s clicking on and off every few minutes, that short-cycling is a problem worth diagnosing.

You can do a rough check with your hand. Hold it near a supply vent for 30 seconds. There should be a clear, consistent difference between the supply air and room temperature. If supply air feels the same as room temperature and the system has been running for 10 minutes, something is off.

Specific things to check

Circuit breakers. Check both the indoor air handler breaker and the outdoor unit breaker at your panel. Also look for a disconnect box near the outdoor unit (it looks like a small gray box on the wall). The disconnect can get flipped without you knowing, especially after any yard work.

Refrigerant line insulation. Two copper lines run from the outdoor unit into the house. The larger one (the suction line) should have intact foam insulation around it. If it’s cracked, torn, or missing, you’re losing efficiency. It won’t cause an immediate breakdown, but it’s worth noting.

Outdoor unit clearance. The unit needs adequate clear space around it on all sides — check your model’s installation manual for the exact spec, but overgrown shrubs, a stored ladder, or a pile of leaves against the coil will restrict airflow and make the system work harder. This is an easy self-fix.

Unusual sounds. A low hum is normal. A grinding or screeching noise usually points to a motor bearing. A rattling sound is often a loose panel or debris inside the unit. A gurgling or hissing sound could be refrigerant-related and needs a tech.

What you can’t check yourself

Refrigerant level is the big one. Low refrigerant is a common cause of poor heating or cooling, but you can’t diagnose it without gauges and EPA 608 certification to handle refrigerants. Symptoms include ice on the indoor coil, longer run times without reaching setpoint, and supply air that never gets warm (or cold) enough. If you’ve ruled out the filter, thermostat, and airflow issues and the system still underperforms, refrigerant charge is the next thing a tech will check.

Electrical components inside the unit, the capacitor, contactor, and control board, also need proper testing equipment. A weak capacitor is extremely common on units over 8-10 years old and shows up as the unit struggling to start or the outdoor fan spinning slowly.

Refrigerant leaks require leak detection equipment. Don’t let anyone just “top off” the refrigerant without finding the source of the loss.

Bay Area context

Mild winters here mean heat pumps often run at part load, which is actually ideal for them. But it also means people sometimes can’t tell if the system is underperforming because the house stays comfortable enough anyway. If your electric bill has spiked without a clear explanation, or if the system runs constantly but barely moves the temperature, those are signs worth investigating even if nothing feels obviously broken.

The other Bay Area quirk: a lot of homes have older single-stage systems that were sized for a gas furnace and then had a heat pump swapped in. If the system is genuinely undersized for the home, no amount of service will fix that, and that’s a conversation worth having with a contractor.

When to call a pro

Call someone if: the outdoor unit is iced over and won’t clear after a full defrost cycle, you hear grinding or screeching, the system runs but supply air is near room temperature for more than 15 minutes, or your breaker trips more than once.

The checks above are safe for any homeowner. Beyond that, leave it to a licensed tech. Refrigerant handling requires EPA 608 certification. Electrical work inside the unit carries real shock risk.

If you’re in the Bay Area and want someone to take a look, we do HVAC diagnostics and repairs at bayareahvacservice.com. We can usually get there same or next day.

Key takeaways

• Check the thermostat mode, air filter, and outdoor unit first — these are the cause of most complaints.
• Heat pump air feels warmer than room temperature but cooler than a gas furnace; that is normal and expected.
• Short-cycling, persistent ice on the outdoor unit, and grinding sounds are the clearest signs something is wrong.
• Refrigerant level and electrical components require a licensed tech with proper equipment.
• Bay Area homeowners often mistake normal part-load operation for underperformance.

Related questions

Written by Andrew Kuznetsov. Andrew is the founder and owner of Bay Area HVAC Service (ADRIUM Service Solutions). He holds a California Contractor License (CSLB #1136642), EPA 608 certification, and completed factory training at the Daikin/Goodman plant in Houston in 2025. He writes from direct field experience, not marketing copy.

Further reading

• Mitsubishi Hyper-Heat (H2i): How It Keeps Putting Out Heat When It Gets Cold in the Bay Area , Most people think heat pumps quit when it gets cold. Mitsubishi's Hyper-Heat (H2i) line is built to keep working as temperatures drop, which matters more here than folks expect, especially on cold mornings and up in the East Bay hills.
• Mitsubishi Mini-Split Blinking a Fault Light? What It Means and What to Do , A blinking light on your Mitsubishi indoor head is the system telling you something is wrong. Here is what the blink pattern means, the checks you can safely do yourself, and when to bring in a factory-trained tech.
• Why Your Mitsubishi Mini-Split Is Leaking Water Inside (and How to Fix It) , A Mitsubishi mini-split dripping water inside almost always comes down to condensate that can't drain. Here's what causes it, the safe checks you can do yourself, and when to call a tech.