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York · YZF42B21S LX Series AC

York YZF42B21S LX Series AC E4 Error Fix: Low Pressure Switch Trip

The low pressure switch has tripped indicating insufficient refrigerant or a blockage in the system. This prevents compressor damage but causes loss of cooling.

critical2 fixes available

Quick Answer

Error E4 on the York YZF42B21S LX Series AC means: Low Pressure Switch Trip. The top-ranked community fix is “Check for Refrigerant Leaks and Recharge” (hard difficulty, ~90 min, DIY cost: $0-$50). 2 community-ranked fixes available below.

Published February 2026 · 2 fixes · air conditioner

Content is based on manufacturer service documentation, community repair experience, and OEM technical bulletins. Always verify with your owner's manual.Learn about our editorial standards.

Root Cause Analysis

Refrigerant IssuePrimary

Drainage Issue → Clogged Drain Filter

When to Call a Professional

While many air conditioner repairs can be done safely at home, consider hiring a qualified technician if:

The repair involves electrical wiring, gas lines, or refrigerant
You've tried the top-ranked fix and the error persists
You smell gas, see sparking, or notice water leaking
The repair requires specialized tools you don't have
Your appliance is still under manufacturer warranty

Average professional repair cost for this issue: $320-$470.

Other York Models with Error E4

DERA-F036N07 14 SEER

air_conditioner · 2 fixes

YHG42B21S 3.5 Ton 14 SEER 10 HSPF Affinity Series Heat Pump with Variable-Speed Compressor

heat_pump · 2 fixes

YZH36B21S 3 Ton 16 SEER 9.5 HSPF Heat Pump with Environmentally Friendly Refrigerant

heat_pump · 2 fixes

Other York YZF42B21S LX Series AC Error Codes

Indoor Temperature Sensor Failure

2 fixes

Outdoor Coil Temperature Sensor Fault

2 fixes

High Pressure Switch Trip

2 fixes

Compressor Overcurrent Protection

2 fixes

Indoor Fan Motor Locked Rotor

2 fixes

Outdoor Fan Motor Locked Rotor

2 fixes

Indoor Coil Freeze Protection Activated

2 fixes

Drain Pump Failure

2 fixes

People Also Ask About York YZF42B21S LX Series AC Error E4

What does error code E4 mean on a York YZF42B21S LX Series AC?

Error code E4 on the York YZF42B21S LX Series AC means: Low Pressure Switch Trip. The low pressure switch has tripped indicating insufficient refrigerant or a blockage in the system. This prevents compressor damage but causes loss of cooling.

How do I fix error code E4 on my York YZF42B21S LX Series AC?

The most successful fix is "Check for Refrigerant Leaks and Recharge" (hard difficulty, ~90 minutes). Estimated DIY cost: $0-$50. HomeMD has 2 community-ranked fixes for this error.

Is error code E4 on a York YZF42B21S LX Series AC serious?

This error is rated critical severity. It is generally not urgent and can often be resolved with a simple DIY fix.

Can I fix York YZF42B21S LX Series AC error E4 myself?

Yes — the top-ranked community fix ("Check for Refrigerant Leaks and Recharge") is rated hard difficulty and takes about 90 minutes. Tools needed: HVAC gauge set, Leak detector, Vacuum pump.

How much does it cost to repair York YZF42B21S LX Series AC error E4?

DIY cost: $0-$50. Professional repair typically costs $320-$470. Many homeowners save money by trying the top-ranked community fix first.

What other error codes does the York YZF42B21S LX Series AC have?

The York YZF42B21S LX Series AC has 8 other known error codes, including: E1 (Indoor Temperature Sensor Failure), E2 (Outdoor Coil Temperature Sensor Fault), E3 (High Pressure Switch Trip), E5 (Compressor Overcurrent Protection), E6 (Indoor Fan Motor Locked Rotor), and 3 more.

Which other York models have the E4 error?

Error code E4 also appears on 3 other York models: DERA-F036N07 14 SEER, YHG42B21S 3.5 Ton 14 SEER 10 HSPF Affinity Series Heat Pump with Variable-Speed Compressor, YZH36B21S 3 Ton 16 SEER 9.5 HSPF Heat Pump with Environmentally Friendly Refrigerant. The fix may vary by model, so check each model's specific page for tailored repair steps.

What other error codes does the York YZF42B21S LX Series AC have?

The York YZF42B21S LX Series AC has 8 other known error codes:

E1 — Indoor Temperature Sensor Failure (2 fixes)
E2 — Outdoor Coil Temperature Sensor Fault (2 fixes)
E3 — High Pressure Switch Trip (2 fixes)
E5 — Compressor Overcurrent Protection (2 fixes)
E6 — Indoor Fan Motor Locked Rotor (2 fixes)
E7 — Outdoor Fan Motor Locked Rotor (2 fixes)
E8 — Indoor Coil Freeze Protection Activated (2 fixes)
E9 — Drain Pump Failure (2 fixes)

Which other York models have the E4 error?

Error code E4 also appears on 3 other York models:

DERA-F036N07 14 SEER (air conditioner) · 2 fixes
YHG42B21S 3.5 Ton 14 SEER 10 HSPF Affinity Series Heat Pump with Variable-Speed Compressor (heat pump) · 2 fixes
YZH36B21S 3 Ton 16 SEER 9.5 HSPF Heat Pump with Environmentally Friendly Refrigerant (heat pump) · 2 fixes

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