In our experience, when the indoor fan is running but the outdoor heat pump is not, the first thing we determine is whether the outdoor unit should actually be running at that moment.
The indoor blower and outdoor heat pump are controlled separately, so air can still come from the vents even when the outdoor unit has lost power, isn’t receiving a call from the thermostat, or has been shut down by one of the system’s safety controls.
Sometimes the outdoor unit stops temporarily without anything being wrong. After a power interruption or recent shutdown, the compressor may wait several minutes before restarting, and during a defrost cycle, the outdoor fan can stop even though the heat pump is still operating.
If the outside unit remains off while the thermostat is calling for heating or cooling, we work through the thermostat settings, outdoor power supply, control signal, and safety controls before moving on to the contactor, capacitor, fan motor, and compressor.
In this guide, we’ll explain the most common reasons the outside heat pump may not be running while the inside fan is, what you can safely check yourself, and when the problem needs professional repair.
Why Is the Inside Fan Running if the Outside Heat Pump Is Not?
The indoor blower and outdoor heat pump do not have to run at the same time.
The blower can keep moving air through your home even when the outdoor unit is off, which is why you may still feel air coming from the vents even though the outdoor heat pump is completely quiet.
One of the first things we check is whether the thermostat is actually calling for the outdoor heat pump or simply running the indoor fan. A fan set to On instead of Auto runs continuously even when there is no heating or cooling call, which we cover in more detail below.
There are also a few situations where the outdoor unit may be off temporarily without anything being wrong.
After a power interruption, breaker reset, thermostat change, or recent heating or cooling cycle, many heat pumps use a built-in compressor protection delay that keeps the compressor off for several minutes.
This prevents the compressor from stopping and restarting under pressure. We sometimes arrive at a system that appears dead outside only to find it is still waiting through this delay, so give the outdoor unit several minutes before assuming it has failed.
In heating mode, we also make sure the outdoor unit is truly off and not just in a normal defrost cycle, during which the outdoor fan stops temporarily while the compressor continues to run.
Heating mode has one more wrinkle worth knowing about. The backup electric heat can keep the house comfortable even when the outdoor heat pump has stopped running entirely. In those cases, the first sign of a problem is often a much higher power bill rather than a cold house.
If the thermostat is calling for heating or cooling and the outdoor unit remains completely silent after a normal restart delay, we start checking power, thermostat controls, safety switches, the contactor, the capacitor, and other components that could keep the heat pump from starting.
Why Is My Outside Heat Pump Not Running?
When the indoor blower is running, but the outdoor heat pump is not, we first determine whether the outdoor unit is being told to run and whether it has the power it needs to start.
From there, the problem usually comes down to a thermostat or control issue, a safety shutoff shutting the system down, a failed electrical component, or a problem with the outdoor fan or compressor.
1. The Thermostat Is Not Calling for the Heat Pump
One of the first things we check is whether the thermostat is actually calling for heating or cooling rather than simply running the indoor fan.
The thermostat should be set to Heat or Cool, depending on the season, with the temperature setting far enough from the current indoor temperature for the system to turn on.
We also check whether the fan is set to On. With that setting, the indoor blower can run continuously even when the thermostat is not asking the outdoor heat pump to do anything. The Auto setting lets the fan cycle with the heating or cooling system instead.
In heating mode, we check that the thermostat has not been switched to Emergency Heat. On many heat pump systems, Emergency Heat uses the backup heating source and intentionally keeps the outdoor heat pump off.
If the thermostat was recently replaced or reconfigured, we also look at its heat-pump settings and wiring. A thermostat can appear to work normally while failing to send the correct signal to the outdoor equipment.
2. The Outdoor Unit Has Lost Power
The indoor and outdoor portions of a heat pump can have separate electrical circuits. That means the air handler may continue running even if the outdoor heat pump has lost power completely.
When the outdoor unit is totally silent, we check whether it is receiving the correct electrical supply.
Possible causes include:
- a tripped breaker;
- a problem at the outdoor disconnect;
- a blown fuse on systems that use one;
- a loose or damaged electrical connection;
- an electrical component that caused the circuit to trip.
In the Upstate, summer thunderstorms are a common trigger. A surge or brief outage can trip the outdoor breaker on its own, or damage a component that then trips the breaker again once power is restored.
If a breaker has tripped, we do not recommend resetting it repeatedly. A breaker that trips again may be protecting the wiring or equipment from an electrical fault, and the cause should be diagnosed before the system continues running.
3. A Condensate Safety Switch Has Shut the System Down
During cooling season, a clogged condensate drain can sometimes explain why the indoor system appears to have power while the outdoor unit will not start.
Heat pumps remove moisture from the indoor air while cooling. That water normally drains away through the condensate line. If the line becomes clogged and water begins backing up, many systems have a float switch that shuts down part or all of the cooling equipment before the drain pan overflows.
When we see an outdoor unit that has unexpectedly stopped during humid weather, one of the things we look for is water in the drain pan or a backed-up condensate line. Greenville summers produce a lot of condensate, so this is a frequent find from June through September.
The fix is not to bypass or hold down the float switch. We need to correct the drainage problem that caused the safety switch to open in the first place.
4. The Outdoor Unit Is Not Receiving the Control Signal
Sometimes the heat pump has electrical power available, but it is not receiving the low-voltage signal that tells it to start.
When we diagnose this condition, we trace the call from the thermostat through the indoor equipment and out to the heat pump.
The problem can be caused by:
- damaged thermostat wiring
- a loose low-voltage connection
- a blown low-voltage fuse
- a transformer problem
- an indoor control-board issue
- wiring damaged outside
- a problem introduced during recent thermostat or HVAC work
This is one reason we do not assume a completely silent outdoor unit automatically has a bad compressor. If the start signal never reaches the unit, the compressor has never been given the opportunity to run.
5. A Safety Control Has Locked the Heat Pump Out
Heat pumps have controls designed to stop the compressor when operating conditions could damage the system.
Depending on the equipment, that can include high- and low-pressure protection, temperature sensors, compressor overload protection, and fault logic built into the heat pump’s control board.
When we find that the unit has power and is receiving a call from the thermostat but still will not operate, we check whether one of these protections has shut it down.
The safety itself is not always the underlying problem. A pressure safety may be responding to low refrigerant, an outdoor fan problem, restricted airflow, or another refrigeration issue.
Around Greenville, one of the most common reasons we find a high-pressure safety open is an outdoor coil packed with spring pollen, cottonwood, or grass clippings that keeps the unit from shedding heat.
A reset that skips the question of why the system shut down can allow the same problem to happen again.
6. The Contactor Is Not Working
The contactor is an electrical switch inside the outdoor unit that allows power to reach the compressor and outdoor fan when the thermostat calls for heating or cooling.
When we troubleshoot a heat pump that will not start, the contactor helps us narrow down the problem.
If the outdoor unit is completely silent, the contactor may not be receiving the control signal or its coil may have failed.
If we hear the contactor click, but neither the fan nor compressor starts, we check whether power is actually passing through it and whether the problem is farther downstream.
Contactors can wear, pit, or fail electrically over time. Ants and other insects can also bridge the contacts. It is a relatively common repair compared with major components such as the compressor, and a replacement typically runs $200 to $450 installed.
7. The Capacitor Has Failed
The capacitor helps the outdoor fan motor and compressor start and run properly.
When the contactor engages but the outdoor unit only hums, buzzes, or tries to start without getting going, the capacitor is one of the first components we test.
Depending on the type of capacitor and what has failed, we may find:
- the outdoor fan will not start;
- the compressor will not start;
- both appear dead even though the contactor has engaged;
- the unit starts intermittently and then stops working again.
If the outdoor unit is humming with the fan stopped, turn the system off at the thermostat until it can be checked. Running it in that condition can overheat the compressor.
A capacitor can hold an electrical charge even after power has been disconnected, so we don’t recommend opening the outdoor unit to test it yourself.
We also do not recommend the common online advice of pushing the outdoor fan blade with a stick to see whether it starts. That does not safely diagnose the problem and puts you close to moving equipment and live electrical components.
Capacitor replacement is one of the less expensive heat pump repairs, usually $150 to $350 depending on the type and location, and it can often be completed the same day.
8. The Outdoor Fan Motor Has Failed
A stopped outdoor fan does not necessarily mean the entire heat pump is off.
During a normal defrost cycle in heating mode, the outdoor fan may temporarily stop while the compressor continues operating. If the fan starts again after defrost ends, that can be normal.
Outside of defrost, however, a fan that should be running but is not can point to a failed capacitor, fan motor, wiring problem, or control issue.
One thing we listen for is whether the compressor is still running even though the fan is stationary. If it is, the heat pump may quickly build excessive pressure or temperature and eventually shut itself down on a safety control.
A coil already coated in pollen or debris makes that happen faster. That can make the problem progress from a stopped fan to what looks like an entirely dead outdoor unit.
Outdoor fan motor replacement typically runs $300 to $650 depending on the motor type and the unit.
9. A Refrigerant Problem Has Shut the Compressor Down
Low refrigerant rarely makes the outdoor unit go completely dead as a first symptom.
More often, we find the heat pump losing heating or cooling capacity, running for long periods, icing abnormally, or cycling before it eventually stops.
If refrigerant pressure falls outside the range the system is designed to operate in, the same pressure controls described above may shut down the compressor to protect it.
Low refrigerant also means there is usually a leak somewhere in what should be a sealed system. A recharge that skips the question of why the charge is low does not address the underlying problem.
We have to test the refrigeration system to determine whether refrigerant pressure is actually responsible for the shutdown and where the problem is coming from. The cost depends on where the leak is and how much refrigerant the system holds.
A minor leak repair and recharge may be a few hundred dollars, while a coil replacement can run well over a thousand.
10. The Compressor Cannot Start or Has Failed
A failed compressor is possible, but it is not the first conclusion we jump to when the outdoor heat pump will not run.
Before we condemn a compressor, we want to know that the thermostat is calling for it, the outdoor unit has the correct power, the safety circuit is allowing operation, the contactor is working, and the starting components are doing what they should.
If all of those checks are normal but the compressor still cannot start, we begin testing the compressor itself.
Depending on the failure, we may find that the compressor:
- hums but cannot start;
- draws excessive electrical current;
- repeatedly trips its internal overload;
- trips the breaker;
- has damaged electrical windings;
- has failed mechanically.
A compressor is one of the more expensive components in a heat pump. Replacement commonly runs $1,500 to $2,800 or more depending on the system, so on an older unit, we will usually weigh the age and overall condition of the equipment along with the cost of the repair before recommending how to proceed.
What Can You Check Yourself When the Outside Heat Pump Is Not Running?
There are a few things you can safely check before calling for service, especially if the outdoor heat pump stopped suddenly, but the indoor blower is still running.
We recommend checking:
- that the thermostat is set to Heat or Cool, depending on what you are trying to do;
- that the temperature setting is far enough from the current indoor temperature for the system to call for heating or cooling;
- that the fan is set to Auto rather than On;
- whether Emergency Heat has been selected;
- whether the thermostat shows a delay, wait, or similar message after a recent outage or restart;
- whether the outdoor unit starts after several minutes, once it has had time to come out of a compressor protection delay;
- whether the outdoor breaker has tripped;
- whether leaves, pollen, grass clippings, or other debris are blocking airflow around the outdoor unit;
- during cooling season, whether there is standing water in the auxiliary drain pan or another obvious sign that the condensate drain is backed up.
Pay attention to what the outdoor unit is doing, not just whether the fan is spinning. If you hear the compressor running but the outdoor fan is stopped, that points us in a different direction than a unit that is completely silent.
There are several things we do not recommend trying yourself.
Do not remove the outdoor service panel, touch or test the capacitor, manually push in the contactor, jumper thermostat wires, bypass a float or pressure switch, push the fan blade with a stick, connect refrigerant gauges, or reset a tripped breaker more than once.
If the thermostat settings are correct, the system has had enough time to restart, and the outdoor unit still will not run, the next step is to determine whether it is receiving power and a control signal, and whether one of the system’s electrical or safety components is preventing it from starting.
When Should You Call for Heat Pump Repair?
If the indoor blower is running but the outdoor heat pump still will not start after the basic checks, the problem usually needs to be diagnosed rather than guessed at.
We recommend calling for service when:
- the outdoor unit remains completely silent after a normal restart delay;
- the thermostat is calling for heating or cooling, but the outdoor unit does not respond;
- the breaker has tripped;
- the unit clicks, hums, or buzzes but does not start;
- the outdoor fan is not running outside of a normal defrost cycle;
- the system starts and then shuts itself back down repeatedly;
- you see heavy ice on the outdoor unit;
- a condensate safety switch keeps shutting the system down;
- you notice a burning or electrical smell;
- Emergency Heat is keeping the house warm because the heat pump won’t run.
The repair cost depends heavily on what we find. A thermostat, contactor, capacitor, or control issue is usually much less involved than a refrigerant leak, failed fan motor, or compressor problem.
On an older heat pump, we may also compare the repair cost with the system’s age and overall condition before recommending whether it makes more sense to repair or replace it.
The important thing is not to assume that a quiet outdoor unit means the compressor has failed. We often find simpler electrical, control, or safety issues that produce the same symptom.
Outside Heat Pump Not Running in Greenville? Call Air Today
If the inside fan is running but the outside heat pump is not, the first step is finding out whether the outdoor unit is being called, whether it has power, and whether a control or safety issue is preventing it from starting.
Air Today Heating & Cooling provides heat pump repair throughout Greenville and the Upstate. We identify the cause before recommending a repair, and we will tell you when a simple fix is all the system needs.
Call 864-295-0905 or contact Air Today Heating & Cooling to schedule heat pump service.