Hyper hypothermia machines · Medi-Therm family

Stryker Medi-Therm III: troubleshooting and error codes

The ServiceForge knowledge base holds 12 documented symptoms for the Stryker Medi-Therm III, with 43 ranked causes, 35 diagnostic checks with test points and expected values, and 8 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Blanket will not cool

Cooling system does not function; blanket does not reach target cold temperature.

Ranked causes

1. Compressor not running (common)
2. No line voltage at TB1 terminals 1 and 3 (cold solenoid circuit) (common)
3. Cold solenoid SV1 not energized (common)
4. Cold solenoid SV1 coil shorted (occasional)
5. No line voltage at Q9 output (Q9 or U8 damaged) (occasional)
6. Pump not running or inadequate flow (occasional)
7. Reservoir temperature not reaching target cold temperature (occasional)

First check

Verify compressor is operating

Test point: Compressor motor
Expected: Compressor running

6 more checks with pass and fail actions, 7 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Pump motor not running

Pump does not operate in AUTO or MANUAL modes; no water circulation.

Ranked causes

1. No line voltage at TB1 terminals 6 and 8 (common)
2. No line voltage at Q4 output (common)
3. Optocoupler U2 input not pulled low (occasional)
4. Pin 8 of U51 not 0 VDC relative to pin 10 (occasional)
5. Pump winding shorted (occasional)
6. Q4 or U2 damaged (rare)

First check

Verify operating mode selection

Test point: Unit mode selector
Expected: AUTO or MANUAL

5 more checks with pass and fail actions, 6 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

RFU Code 1: Temperature reading out of range

Machine displays RFU Code 1 when measured values from RT1 or RT2 are not within 32°F and 122°F (0°C and 50°C).

Ranked causes

1. RT1 sensor reading out of range (common)
2. RT2 sensor reading out of range (common)
3. Faulty signal lines between control/display board and RT1 (occasional)
4. Faulty signal lines between control/display board and RT2 (occasional)
5. Temperature measurement circuitry fault (occasional)
6. Controller failure (rare)

First check

Measure RT1 resistance between pins 2 and 9 of connector P6

Test point: P6 pins 2 and 9
Expected: between 811 and 7355 ohms, 811-7355

3 more checks with pass and fail actions, 6 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Blanket will not heat in AUTO or MANUAL mode

Heating system does not function; blanket remains at ambient temperature in heating modes.

Ranked causes

1. No line voltage at TB1 terminals 2 and 3 (common)
2. Heater is energized when it should be off (common)
3. Pump not running (common)
4. Inadequate water flow through heating circuit (occasional)

First check

Measure line voltage at heater circuit

Test point: TB1 terminals 2 and 3
Expected: Line voltage present

3 more checks with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

RFU Code 8: Blanket probe reading faulty

Machine displays RFU Code 8 when blanket probe (RT2) reading is faulty.

Ranked causes

1. RT2 blanket probe malfunction (common)
2. Faulty signal lines between control/display board and RT2 (occasional)
3. Temperature measurement circuitry fault (occasional)
4. Controller failure caused RT2 out of range (rare)

First check

Disconnect connector P6 from J2 and measure resistance between pins 3 and 5 of connector P6

Test point: P6 pins 3 and 5
Expected: between 811 and 7355 ohms, 811-7355

1 more check with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

RFU Code 9: Reservoir probe reading faulty

Machine displays RFU Code 9 when reservoir probe (RT1) reading is faulty.

Ranked causes

1. RT1 reservoir probe malfunction (common)
2. Faulty signal lines between control/display board and RT1 (occasional)
3. Temperature measurement circuitry fault (occasional)
4. Controller failure caused RT1 out of range (rare)

First check

Disconnect connector P6 from J2 and measure resistance between pins 2 and 9 of connector P6

Test point: P6 pins 2 and 9
Expected: between 811 and 7355 ohms, 811-7355

1 more check with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

RFU Code H: S1 thermostat open

Machine displays RFU Code H with S1 low temperature thermostat stuck open.

Ranked causes

1. S1 low temperature thermostat out of specification or stuck open (common)
2. S2 or S3 high temperature thermostat out of specification (occasional)
3. Temperature measurement failure or control system fault (rare)

First check

Operate unit in MANUAL mode with setpoint temperature equal to 39.2°F (4°C) and verify TP9 temperature

Test point: TP9
Expected: less than 37.4°F (3°C)

4 more checks with pass and fail actions, 5 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

RFU Code 4: Compensation resistor 1 reading too high

Machine displays RFU Code 4 when R12 compensation resistor on control/display board reads too high.

Ranked causes

1. R12 compensation resistor out of specification (common)
2. Temperature measurement circuitry fault (occasional)

First check

Measure R12 resistance

Test point: R12 on control/display board
Expected: 816 ohms ±0.1%, ±0.1%

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

RFU Code 5: Compensation resistor 1 reading too low

Machine displays RFU Code 5 when R12 compensation resistor on control/display board reads too low.

Ranked causes

1. R12 compensation resistor out of specification (common)
2. Temperature measurement circuitry fault (occasional)

First check

Measure R12 resistance

Test point: R12 on control/display board
Expected: 816 ohms ±0.1%, ±0.1%

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

RFU Code 6: Compensation resistor 2 reading too high

Machine displays RFU Code 6 when R13 compensation resistor on control/display board reads too high.

Ranked causes

1. R13 compensation resistor out of specification (common)
2. Temperature measurement circuitry fault (occasional)

First check

Measure R13 resistance

Test point: R13 on control/display board
Expected: 7320 ohms ±0.1%, ±0.1%

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

RFU Code 7: Compensation resistor 2 reading too low

Machine displays RFU Code 7 when R13 compensation resistor on control/display board reads too low.

Ranked causes

1. R13 compensation resistor out of specification (common)
2. Temperature measurement circuitry fault (occasional)

First check

Measure R13 resistance

Test point: R13 on control/display board
Expected: 7320 ohms ±0.1%, ±0.1%

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Blanket display temperature not matching setpoint patient safety

Blanket temperature display shows significant deviation from setpoint; does not stabilize within acceptable range.

Ranked causes

1. Temperature sensor RT2 reading inaccurate (occasional)

First check

Compare blanket display temperature to setpoint and independent thermometer

Test point: Blanket display and separate thermometer probe in blanket
Expected: Display within 1.8°F (1°C) of setpoint; matches independent reading

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Error codes

Code	Meaning	Trigger	Severity
`RFU Code 1`	Measured values from RT1 or RT2 are not within 32°F and 122°F (0°C and 50°C).	Temperature sensor reading out of specification or faulty signal path	error
`RFU Code 4`	Compensation resistor 1 (R12 on control/display board) reading is too high	R12 resistance exceeds specification during temperature measurement circuit self-test	error
`RFU Code 5`	Compensation resistor 1 (R12 on control/display board) reading is too low	R12 resistance is below specification during temperature measurement circuit self-test	error
`RFU Code 6`	Compensation resistor 2 (R13 on control/display board) reading is too high	R13 resistance exceeds specification during temperature measurement circuit self-test	error
`RFU Code 7`	Compensation resistor 2 (R13 on control/display board) reading is too low	R13 resistance is below specification during temperature measurement circuit self-test	error
`RFU Code 8`	Blanket probe (RT2) reading faulty	Blanket temperature probe malfunction or signal path failure detected during operation	error
`RFU Code 9`	Reservoir probe (RT1) reading faulty	Reservoir temperature probe malfunction or signal path failure detected during operation	error
`RFU Code H`	S1 low temperature thermostat stuck open or out of specification	S1 thermostat fails to close when setpoint is reached or remains open during normal operation	error

Likely causes and actions for each code are in ServiceForge. Connect ServiceForge to your AI

Community

0 fixes logged by technicians through their AI, with outcomes, for this model.

ServiceForge knowledge base record. Field-unverified unless technicians confirmed it. A teaching summary of the record, not a service manual. Export 2026-10-14.