SDHVD1S / SCHVD1S — Intermittent Low‑Airflow & “Fan Won’t Ramp” Diagnostic Guide
(Applies to all SDHV indoor units SDHV07–16D1S (single‑phase) & SDHV20–24D1S (three‑phase), and all matching SCHV outdoor units.)
About This Guide
This guide explains how to diagnose and correct the most common causes of intermittent low airflow and indoor fans not ramping to higher speeds on SDHVD1S ducted indoor units paired with SCHVD1S outdoor units. It provides a structured diagnostic workflow covering fan mapping, ESP setup, sensor accuracy, and fan motor behaviour. Commissioning and communication details are referenced only where they directly support airflow recovery.
1) Why SDHVD1S Indoor Fans Stay on Low or Fail to Ramp
SDHVD1S units will intentionally reduce fan output when commissioning parameters, ESP, or thermistor readings fall outside expected ranges. The most frequent causes of “fan stuck on low” or “weak airflow” symptoms include:
- Incorrect fan‑speed mapping
- Incorrect ESP (0–200 Pa typical range)
- Out‑of‑tolerance or poorly placed coil / ambient thermistors
- Fan motor connector or harness intermittency
References: Service Guide Sections 5, 15, 16 (airflow, ESP, commissioning)
2) First Step — Use Native SDHV Controller (AirTouch Disconnected)
Before testing anything:
Isolate AirTouch from the communication bus
(Required to access full SDHV commissioning parameters.)Use the correct controller:
- SDHV 07–16 kW single‑phase → XK60 or XK75
- SDHV 20–24 kW three‑phase → XK46
References: Service Guide Sections 15, 16, 19
This ensures access to ESP configuration, fan curve adjustment, and sensor values.
3) Main Root Causes of Intermittent Low Airflow
Cause 1 — Fan Mapping Incorrect (Common with AirTouch Systems)
If AirTouch fan‑speed assignments do not match the SDHV’s native 9‑step fan curve, the indoor fan may fail to ramp or will ramp inconsistently.
SDHV fan‑speed mapping format:
- 0 = Auto
- 1 = Low
- 2 = Low‑Med
- 3 = Med
- 4 = Med‑High
- 5 = High
- 6 = Turbo
Some models group speeds (e.g., Low = 1–2, Med = 3–4, High = 5–6). Incorrect grouping = no noticeable change.
References: Service Guide Sections 16, 20 (AirTouch)
Quick Check — Verify the Native 9‑Step Fan Curve (Before Reconnecting AirTouch)
- Isolate AirTouch so SDHV can operate independently.
- On XK60/XK75, open commissioning → Fan Steps/Fan Curve (Steps 1–9).
- Run the system in cooling and manually command Steps 1 → 9, pausing 3–5 s each step.
- Expect a distinct airflow/RPM increase for each step.
- Step 9 should reach near rated airflow for the installed SDHVD1S model (see Service Guide Section 5 airflow table).
- Examples: SDHV07 → 417 L/s, SDHV10 → 556 L/s, SDHV16 → 861 L/s.
- If steps don’t change or airflow is weak:
- Set ESP 0–200 Pa to measured duct static
- Remap all 9 fan steps
- Verify thermistor resistance vs Service Guide Section 36
- Check fan motor plug and RPM stability
References: Service Guide Sections 5, 15, 16, 36
Cause 2 — ESP Incorrect or Not Set (0–200 Pa)
Incorrect ESP will cause the indoor fan to clamp to a lower output.
- Measure the actual duct static pressure
- Set ESP inside the SDHV commissioning menu
- Adjust 9 fan steps so HIGH is close to rated airflow for the installed SDHVD1S model (see Service Guide Section 5)
References: Service Guide Section 5
Cause 3 — Coil or Ambient Sensors Out of Tolerance
Incorrect or drifting thermistor values often cause the fan to restrict airflow, even when no fault code appears.
Checks:
- Power OFF
- Disconnect sensors at PCB
- Measure resistance → compared to Thermistor Table (Service Guide Section 36)
- Confirm coil sensor is clipped firmly; ambient sensor positioned correctly
- Wiggle‑test for intermittent readings
References: Service Guide Sections 35, 36
Cause 4 — Fan Motor Connector / Harness Issues
Loose connectors, strained wires, or unstable RPM feedback will prevent the fan from ramping.
Fix:
- Reseat connector
- Inspect harness for corrosion or strain
- Test LOW / MED / HIGH for stable RPM (no H6‑type behaviour)
References: Service Guide Section 35 (H6 context)
4) 15‑Minute Field Diagnostics (All SDHV Models)
Perform these steps in order:
- Isolate AirTouch → restore full SDHV control
- Check thermistor values at indoor PCB (coil & ambient vs Service Guide Section 36).
- Set ESP (0–200 Pa) to measured duct static; map all 9 fan steps.
- Verify fan ramping through Steps 1 → 9.
- Reconnect AirTouch and verify step‑to‑step changes occur.
References: Service Guide Sections 5, 15, 16, 20, 36.
5) Secondary Influences (Supporting Only)
E6 (Communication)
Model pairing, wiring polarity, or third‑party flags can indirectly affect fan behaviour.
References: Service Guide Section 35 (E6)
H6 (Fan Protection)
Indicates mechanical load, wiring issues, or fan motor abnormalities.
References: Service Guide Section 35 (H6).
6) Short Summary (with AirTouch Fan‑Mapping Details)
Why fans stay low: SDHV holds fan speed down when fan mapping, ESP, sensors, or fan harness aren’t right.
First step every time:
- Disconnect AirTouch and use XK60/XK75 (single‑phase) or XK46 (three‑phase).
- This lets you test SDHV’s own 9‑step curve, set ESP, and check sensors.
Most common cause — AirTouch mapping:
- AirTouch speeds (e.g., Low/Med/High) are just pointers to SDHV’s Steps 1–9.
- If multiple AirTouch speeds point to the same step, the fan will sound the same and won’t ramp.
- Recommended baseline links:
- Low → Steps 1–2
- Medium → Steps 3–4
- High → Steps 5–6
- Boost/Max (if used) → Steps 7–9
- After confirming SDHV Steps 1→9 ramp cleanly under the wired controller, fix AirTouch mapping so each AirTouch speed changes an SDHV step on purpose (no duplicates).
Example mapping relationship:
| AirTouch (AT) Speed | SDHV Native Step |
|---|---|
| Low | 1–2 |
| Medium | 3–4 |
| High | 5–6 |
| Boost (if used) | 7–9 |
ESP (0–200 Pa):
- Measure duct static, set ESP to that value, and remap all 9 steps. Wrong ESP makes the unit hold back airflow.
Sensors:
- Measure coil/ambient ohms at PCB, compare to SG 36; correct placement; replace if out or intermittent.
Fan harness/RPM:
- Reseat connector; check for corrosion/strain; confirm stable RPM at LOW/MED/HIGH.
Fastest fix path (covers ~90% of cases):
- Isolate AirTouch → 2) Verify SDHV Steps 1→9 ramp → 3) Set ESP (0–200 Pa) → 4) Correct AT→SDHV mapping → 5) Check sensors → 6) Check fan harness/RPM.
These actions resolve majority of intermittent low‑airflow or no‑ramping complaints across the entire SDHVD1S + SCHVD1S range.