RPSI & EXS Coolers Cutting Out on High Fan Speed LED (A09/24) Due to High Static Pressure – Checking Outlet Capacity

Description

Issue Summary

• RPSI/EXS coolers use direct‑drive ECM motors that maintain constant power and adjust fan speed to overcome airflow restrictions.
• If static pressure is too high (or building pressure is negative), the motor may exceed RPM limits and shut down for safety.
• Common causes: undersized ductwork, too few or closed outlets, tight bends/long runs, jammed weather seal, or extraction fans creating negative pressure.
• Target design: ~80 Pa static pressure at the cooler.

Performance Data @ 80 Pa

Outlet Airflow Guide (Typical Domestic Values)

Calculation: Is Outlet Capacity ≥ Airflow @80 Pa?

1. List all outlets and sizes.

1. Multiply by typical L/s per outlet:
   • 6 × 300 L/s = 1800 L/s
   • 2 × 400 L/s = 800 L/s

1. Compare to the cooler airflow @80 Pa:
   • RPSI2500 = 2130 L/s → PASS
   • RPSI2800 = 2530 L/s → PASS
   • EXS200 = 2320 L/s → PASS

PASS Example

• Outlets: 6 × 350 mm (300 L/s each) + 2 × 400 mm (400 L/s each)
• Total outlet capacity = (6 × 300) + (2 × 400) = 2600 L/s
• Cooler airflow @80 Pa = 2530 L/s (RPSI2800)
• Result: PASS – Outlet capacity exceeds cooler airflow.

FAIL Example

• Outlets: 4 × 350 mm (300 L/s each)
• Total outlet capacity = 4 × 300 = 1200 L/s
• Cooler airflow @80 Pa = 2130 L/s (RPSI2500)
• Result: FAIL – Outlet capacity is less than cooler airflow. Add outlets or upsize existing ones.

If total outlet airflow < cooler airflow:

• Add outlets or upsize existing ones.
• Check duct layout for restrictions (bends, length, diameter).

Quick Reference Table: Outlet Count vs Cooler Airflow

Direct‑Drive Motor – Fan Speed LED Diagnostics (RPSI/RPCQi/EXS)

• Solid green = Normal. Fan speed is within the allowed range for the set speed.
• Flashing green = Over‑speed. Motor is about 20% faster than target; it will shut down in 30 s (sooner at higher speeds). At 30% over target, it stops immediately.
• Off during a run command = Under‑speed. Motor is about 30% slower than target or hasn’t started; it will shut down after ~30 s at high speed (longer at lower speeds).

• High static pressure/restrictions: undersized or squashed duct, tight bends/long runs, too few/closed outlets, short dropper to too few outlets, or weather seal not fully opening.
• Negative building pressure: big extraction fans or lack of relief openings.
• Electrical/mechanical: supply voltage out of spec (≤ 207 V or ≥ 253 V), fan installed backwards, worn bearings or internal motor fault.

• ECM coolers hold a target input power at each set speed. If airflow is restricted, the controller raises RPM to maintain that power. When RPM goes outside ~±20%, the control enters fault mode, showing over/under‑speed and protecting the motor — which is why restricted systems tend to cut‑out on high speed.

1. Confirm total outlet capacity ≥ cooler airflow @80 Pa (see tables above).
2. Verify the weather seal opens fully; inspect for kinks/squash in duct runs.
3. Ensure the home has an exhaust/relief path (crack windows/doors if needed).
4. Check mains voltage is within 230–240 V tolerance.

Preventive Measures

• Confirm outlet capacity ≥ cooler airflow @80 Pa before installation.
• Avoid long restrictive runs; ensure registers fully open.
• Provide adequate exhaust openings to prevent negative pressure.
• Verify weather seal operation and dropper/transition integrity.

How to Test Static Pressure at the Dropper (Step‑by‑Step)

What you need

• A digital manometer (or U‑tube manometer) that reads in Pascal (Pa).
• Flexible pressure tube (the small clear hose that plugs into the manometer).
• 6 mm drill bit and a blanking grommet (or aluminum tape) to seal the hole afterwards.
• A marker and a bit of tape.

Safety first

• Turn OFF power to the cooler at the isolation switch.
• Work from a stable ladder and keep hands clear of moving parts.

Where to make the test hole

• On a down‑discharge dropper: drill on the side wall just beneath the weather seal, roughly 25–50 mm below the seal lip, on a straight section. This reads the plenum static pressure the cooler “sees”, without extra turbulence.
• On top/side‑discharge transitions: pick the first straight section before the first bend/branch, ideally 1–2 duct diameters downstream of the outlet.

Step‑by‑step

1. Drill the hole: Use the 6 mm bit at the location above. Lightly deburr the edges.
2. Insert the tube: Push the manometer tube through so the tip sits flush with the inner wall (don’t poke it far into the airflow). Seal around the tube with a grommet or tape so air can’t leak.
3. Power ON and run High Fan: Set the cooler to fan HIGH (ventilation is fine). Make sure the weather seal opens fully. Wait 2–3 minutes for airflow to settle.
4. Read the pressure: Note the Pa value on the manometer. 
   • Around 80 Pa → Good for domestic systems.
   • >100 Pa → Restriction likely (undersized/squashed duct, tight bends, too few/closed outlets, damper not opening).
   • <50 Pa → Too much outlet area or negative pressure in the house (strong extraction fans, closed windows/doors).
5. Finish up: Turn power OFF, remove the tube, and seal the hole with a blanking grommet (preferred) or aluminum tape.

Quick tips for a clean reading

• Keep the tube tip flush and perpendicular to the airflow—this avoids picking up velocity pressure.
• Don’t measure right next to elbows, take‑offs, dampers, or mesh.
• Check all outlets are open and the home has a relief path (windows/doors cracked open) so the cooler isn’t fighting negative pressure.
• If the reading hunts up and down, take a short 5–10 second average (many digital manometers have a damping setting).