diff --git a/9_Firmware/9_1_Microcontroller/9_1_3_C_Cpp_Code/main.cpp b/9_Firmware/9_1_Microcontroller/9_1_3_C_Cpp_Code/main.cpp
index 305b595..a4f8f40 100644
--- a/9_Firmware/9_1_Microcontroller/9_1_3_C_Cpp_Code/main.cpp
+++ b/9_Firmware/9_1_Microcontroller/9_1_3_C_Cpp_Code/main.cpp
@@ -2179,16 +2179,25 @@ int main(void)
 		      DIAG("PA", "System temperature (max of 8 sensors) = %.1f C", (double)temperature);
 		  }
 
-		  //(20 mV/°C on TMP37) QPA2962 RF amplifier Operating Temp. Range, TBASE min−40 normal+25 max+85 °C
-		  int Max_Temp = 25;
-		  if((Temperature_1>Max_Temp)||(Temperature_2>Max_Temp)||(Temperature_3>Max_Temp)||(Temperature_4>Max_Temp)
-				  ||(Temperature_5>Max_Temp)||(Temperature_6>Max_Temp)||(Temperature_7>Max_Temp)||(Temperature_8>Max_Temp))
-			{
+		  // MCU-A1: production thermal limits for QPA2962 (TBASE max +85 °C).
+		  // Cooling fan turns ON at 70 °C and OFF at 60 °C — 10 °C hysteresis
+		  // prevents relay/fan chatter near the threshold. The system-level
+		  // hard overtemp gate at checkSystemHealth() (>75 °C → SAFE mode)
+		  // sits above the cooling ON point so the fan gets a chance to act
+		  // before shutdown. Was previously a 25 °C dev-bench stub that kept
+		  // the fan latched on at room temperature.
+		  static bool cooling_on = false;
+		  const float COOLING_ON_C  = 70.0f;
+		  const float COOLING_OFF_C = 60.0f;
+		  float t_max = temperature;  // populated above as max of 8 sensors
+		  if (!cooling_on && t_max > COOLING_ON_C) {
+			  cooling_on = true;
 			  HAL_GPIO_WritePin(EN_DIS_COOLING_GPIO_Port, EN_DIS_COOLING_Pin, GPIO_PIN_SET);
-			  DIAG_WARN("PA", "Over-temp detected (>%d C) -- cooling ENABLED", Max_Temp);
-			}
-		  else{
+			  DIAG_WARN("PA", "Over-temp %.1f C > %.0f C -- cooling ENABLED", (double)t_max, (double)COOLING_ON_C);
+		  } else if (cooling_on && t_max < COOLING_OFF_C) {
+			  cooling_on = false;
 			  HAL_GPIO_WritePin(EN_DIS_COOLING_GPIO_Port, EN_DIS_COOLING_Pin, GPIO_PIN_RESET);
+			  DIAG("PA", "Temp %.1f C < %.0f C -- cooling DISABLED", (double)t_max, (double)COOLING_OFF_C);
 		  }
 
 		  /* [GAP-3 FIX 4] Periodic IDQ re-read — the Idq_reading[] array was only
diff --git a/9_Firmware/9_1_Microcontroller/tests/Makefile b/9_Firmware/9_1_Microcontroller/tests/Makefile
index a7ce6ad..da60cde 100644
--- a/9_Firmware/9_1_Microcontroller/tests/Makefile
+++ b/9_Firmware/9_1_Microcontroller/tests/Makefile
@@ -66,6 +66,7 @@ TESTS_MOCK_ONLY := test_bug2_ad9523_double_setup \
 TESTS_STANDALONE := test_bug12_pa_cal_loop_inverted \
                     test_bug13_dac2_adc_buffer_mismatch \
                     test_bug16_runradar_shadows_globals \
+                    test_mcu_a1_cooling_hysteresis \
                     test_gap3_iwdg_config \
                     test_gap3_temperature_max \
                     test_gap3_idq_periodic_reread \
@@ -159,6 +160,9 @@ test_bug13_dac2_adc_buffer_mismatch: test_bug13_dac2_adc_buffer_mismatch.c
 test_bug16_runradar_shadows_globals: test_bug16_runradar_shadows_globals.c
 	$(CC) $(CFLAGS) $< -o $@
 
+test_mcu_a1_cooling_hysteresis: test_mcu_a1_cooling_hysteresis.c
+	$(CC) $(CFLAGS) $< -o $@
+
 # Gap-3 safety tests -- mock-only (needs spy log for GPIO sequence)
 test_gap3_emergency_stop_rails: test_gap3_emergency_stop_rails.c $(MOCK_OBJS)
 	$(CC) $(CFLAGS) $(INCLUDES) $< $(MOCK_OBJS) -o $@
diff --git a/9_Firmware/9_1_Microcontroller/tests/test_mcu_a1_cooling_hysteresis.c b/9_Firmware/9_1_Microcontroller/tests/test_mcu_a1_cooling_hysteresis.c
new file mode 100644
index 0000000..bd3a122
--- /dev/null
+++ b/9_Firmware/9_1_Microcontroller/tests/test_mcu_a1_cooling_hysteresis.c
@@ -0,0 +1,95 @@
+/*******************************************************************************
+ * test_mcu_a1_cooling_hysteresis.c
+ *
+ * MCU-A1: cooling-fan threshold was a 25 C dev stub that latched the fan ON
+ * at room temperature. Production fix raises the threshold to 70 C with a
+ * 60 C off point (10 C hysteresis) so the fan does not chatter near the
+ * trip point.
+ *
+ * This test replays the fixed cooling-control logic against a temperature
+ * sweep and asserts (a) the fan stays off below the ON threshold from cold,
+ * (b) it engages crossing 70 C upward, (c) it stays on through the 60-70 C
+ * dead-band on the way down, and (d) it disengages below 60 C.
+ ******************************************************************************/
+#include <assert.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+static const float COOLING_ON_C  = 70.0f;
+static const float COOLING_OFF_C = 60.0f;
+
+/* Replays the post-fix cooling control inside main.cpp:2183-... */
+static bool step_cooling(bool cooling_on, float t_max)
+{
+    if (!cooling_on && t_max > COOLING_ON_C)       return true;
+    else if (cooling_on && t_max < COOLING_OFF_C)  return false;
+    return cooling_on;
+}
+
+int main(void)
+{
+    printf("=== MCU-A1: cooling-fan hysteresis (70 C ON / 60 C OFF) ===\n");
+
+    bool fan = false;
+
+    /* 1. Cold start: room temperature must NOT engage the fan
+     * (this is the bug the 25 C stub caused). */
+    printf("  Test 1: 25 C from cold ... ");
+    fan = step_cooling(fan, 25.0f);
+    assert(fan == false);
+    printf("OFF, PASS\n");
+
+    /* 2. Walking up through the dead band must not engage. */
+    printf("  Test 2: 65 C from cold ... ");
+    fan = step_cooling(fan, 65.0f);
+    assert(fan == false);
+    printf("OFF, PASS\n");
+
+    /* 3. At the exact threshold (>, not >=) still off. */
+    printf("  Test 3: 70.0 C exactly ... ");
+    fan = step_cooling(fan, 70.0f);
+    assert(fan == false);
+    printf("OFF, PASS\n");
+
+    /* 4. Crossing the trip point upward engages. */
+    printf("  Test 4: 70.5 C ... ");
+    fan = step_cooling(fan, 70.5f);
+    assert(fan == true);
+    printf("ON, PASS\n");
+
+    /* 5. Cooling off into the dead band — fan must stay on. */
+    printf("  Test 5: 65 C while ON ... ");
+    fan = step_cooling(fan, 65.0f);
+    assert(fan == true);
+    printf("ON (hysteresis), PASS\n");
+
+    /* 6. At the OFF threshold exactly, still on (uses <, not <=). */
+    printf("  Test 6: 60.0 C exactly while ON ... ");
+    fan = step_cooling(fan, 60.0f);
+    assert(fan == true);
+    printf("ON, PASS\n");
+
+    /* 7. Crossing the OFF point disengages. */
+    printf("  Test 7: 59.5 C while ON ... ");
+    fan = step_cooling(fan, 59.5f);
+    assert(fan == false);
+    printf("OFF, PASS\n");
+
+    /* 8. Spike-and-recover above the system overtemp gate (75 C) — the
+     * fan engages well before checkSystemHealth() trips SAFE mode. */
+    printf("  Test 8: 76 C engages cooling before 75 C SAFE-mode gate ... ");
+    fan = step_cooling(fan, 76.0f);
+    assert(fan == true);
+    printf("ON, PASS\n");
+
+    /* 9. The pre-fix 25 C stub would have set fan=true here. Confirm the
+     * fixed logic does not. */
+    printf("  Test 9: 30 C does NOT engage (regression guard for 25 C stub) ... ");
+    fan = false;
+    fan = step_cooling(fan, 30.0f);
+    assert(fan == false);
+    printf("OFF, PASS\n");
+
+    printf("\n=== MCU-A1: ALL TESTS PASSED ===\n\n");
+    return 0;
+}