Honeywell T4 Pro Replaces an 8-Year-Old Thermostat Calling for Heat and Cool Simultaneously: AC Repair on W Powhatan Ave, Tampa, FL 33614

A thermostat that sends simultaneous heat and cool calls keeps the blower running non-stop even after the house reaches the set temperature — and the fix is a thermostat replacement, not a compressor or refrigerant repair. On March 23, 2026, our technician Barbaro G. arrived at a home on W Powhatan Ave in Tampa, FL 33614 after the homeowner described an AC system that cooled the house but never shut off. After 120 minutes on site, Barbaro traced the root cause to an 8-year-old thermostat with a failed internal relay that was simultaneously calling for both heat and cooling. A Honeywell T4 Pro programmable thermostat replacement restored normal operation. Total invoice: $369. Call (813) 343-2212 for a FREE diagnosis when you hire us.

What the Homeowner Described: An AC That Cooled but Never Stopped Running

The homeowner at this W Powhatan Ave home — who explained the situation in Spanish — described the problem clearly: the air was cold, the house felt comfortable, but the system simply never cycled off. The indoor blower fan ran continuously regardless of what temperature the thermostat was set to.

That description is an important diagnostic clue. When a system cools correctly but the blower won’t stop, the issue is almost never the compressor, the refrigerant, or the coil. Those components affect temperature. A blower that runs without stopping points to the control signal — specifically, the command the thermostat is sending to the air handler.

The homeowner asked specifically that we call before proceeding with any expensive repair. That is exactly how we operate: FREE diagnosis when you hire us, and no additional work begins without clear approval and a quoted price.

How Barbaro G. Traced the Failure to the Thermostat in 120 Minutes

Because the system was producing cold air normally, Barbaro focused the diagnostic on controls rather than major HVAC components. The diagnostic sequence on W Powhatan Ave followed standard HVAC troubleshooting logic for a continuous-blower complaint:

1. Confirm the thermostat mode and settings: Verify the system was set to COOL (not FAN ON) and that the set-point was above the current room temperature. It was — and the fan still ran.
2. Read the thermostat’s output signals: Check which wires are energized at the thermostat terminals. On a standard 24V thermostat, the Y terminal energizes the compressor and G terminal energizes the blower. The W terminal calls for heat. Barbaro found that both the Y/G (cooling/fan) circuit AND the W (heat) circuit were simultaneously energized — the thermostat was calling for both modes at once.
3. Verify the air handler control board: Confirm the board itself was not generating the spurious signal. When the thermostat was disconnected from the wiring, the blower stopped. That confirms the problem was the thermostat’s output, not the board.
4. Confirm equipment function: With a known-good signal applied, the compressor and blower cycled normally. The rest of the 8-year-old system was functioning correctly.

Root cause confirmed: The thermostat’s internal relay contacts had degraded to the point where both the heat and cool circuits were energized simultaneously. This kept the W terminal energized at all times, which held the blower on and quietly activated heat mode even while the compressor was cooling — a particularly inefficient and wasteful failure mode in Tampa’s summer heat.

The Honeywell T4 Pro Thermostat Replacement: What Was Installed and Why

With the diagnosis confirmed and the homeowner approving the repair by phone, Barbaro installed a Honeywell T4 Pro programmable thermostat. This is one of the most reliable entry-level programmable thermostats available for standard split-system HVAC setups in Florida — simple, durable, and compatible with most residential systems including heat pump configurations.

The installation process on W Powhatan Ave followed the same steps used on every thermostat swap:

1. Safely isolate power to the air handler before working on low-voltage wiring
2. Remove the old thermostat and photograph the wiring before disconnecting
3. Label each wire by its terminal designation and inspect for damage or improper splices
4. Mount the new thermostat base, reconnect wiring to correct terminals
5. Configure for the correct system type (cooling only, heat pump, or conventional heat/cool)
6. Test all modes: cool, heat, fan auto, and fan on
7. Verify system shuts off cleanly when set temperature is reached
8. Walk the homeowner through basic thermostat operation and programming

Why This Thermostat Failure Mode Is More Common in Tampa’s 9-Month Cooling Season

Most homeowners think thermostat failures are all the same: the display goes blank, the buttons stop responding, or the system doesn’t start. The dual-call failure Barbaro found on W Powhatan Ave is less obvious and harder to diagnose without checking signal output directly.

In Tampa, FL 33614 and throughout the 33614 ZIP code — which covers neighborhoods including Carrollwood South, Town ‘n’ Country, and areas along the Hillsborough/Pinellas county line — HVAC systems run almost continuously from April through November. That extended duty cycle puts real stress on thermostat relay contacts. According to the U.S. Department of Energy’s guidance on thermostats, relay components in older mechanical or hybrid thermostats are among the first to degrade under continuous cycling loads.

When relay contacts pit or carbon-coat from arcing, they can fail in the “closed” position — meaning the circuit stays energized even when the thermostat intends to turn it off. That is what happened here. The heat relay stuck in the closed position while the system was simultaneously running the cooling cycle, resulting in a system that fought itself and consumed significantly more energy than it should have.

Key Takeaways From This Tampa, FL 33614 Thermostat Repair

• The AC was not broken — refrigerant, compressor, and air handler were all functioning normally. This was a pure controls failure.
• Simultaneous heat-and-cool call is a known relay failure mode, more common in systems with 7+ years of heavy Florida cycling.
• Catching this early matters: a blower running 24/7 in heat+cool mode wastes electricity and puts unnecessary wear on the blower motor. If this Tampa homeowner’s system had run in this state through summer, the blower motor would have been at elevated risk.
• Thermostat replacement resolved the issue completely: Barbaro confirmed normal cycling before leaving the W Powhatan Ave property.
• Total cost: $369, covered by a 5-year parts and 1-year labor warranty through Home Therapist.
• Free diagnosis when you hire us — call (813) 343-2212.

How Much Does a Thermostat Replacement Cost in Tampa, FL?

The $369 on this W Powhatan Ave job is at the lower end of the range for thermostat diagnosis and replacement in Tampa Bay, which reflects the straightforward nature of this particular failure mode. Here is the broader context for thermostat-related repair costs in 33614 and surrounding Hillsborough County ZIP codes:

For more context on what AC repairs cost in the Tampa area, visit our AC repair Tampa service page or our AC maintenance Tampa page for prevention-focused guidance.

Should You Replace an Aging Thermostat in Your Tampa Home Proactively?

Most thermostats in Tampa Bay homes are replaced reactively — after they fail. But given how inexpensive a basic programmable replacement is ($279–$399 installed) compared to the symptoms a failing thermostat can cause, proactive replacement at the 8–10 year mark is worth considering. Signs that a thermostat may be approaching the end of its useful life in a Florida home include:

• Inconsistent temperature readings or incorrect room-temperature display
• System short-cycling (turning on and off rapidly) or running too long without shutting off
• Buttons that are sticky, unresponsive, or require multiple presses
• A display that flickers, dims, or goes blank intermittently
• System behavior that does not match thermostat settings

Any of these symptoms in a 33614 home warrant a call. Our techs carry replacement thermostats on every HVAC van. In many cases, a same-day replacement is available. You can read more about preventive HVAC care on our AC maintenance Tampa FL page or call us directly at (813) 343-2212.

Related: AC services.

Sources: ENERGY STAR.