How do I turn the fan on?

I have a fairly oldish system76 laptop and the fan does not turn on automatically any longer, so the CPU overheats and the laptop powers off all the time.

I opened it and cleaned it from dust. I also followed the instructions in How to control fan speed? and it worked. Once. I.e., I (as root) installed the lm-sensors and fancontrol packages, ran sensors-detect, had it add coretemp to /etc/modules, ran service kmod start, ran pwmconfig, then fancontrol turned the fan on - I heard the noise, I felt the hot air escape the exhaust opening, and the laptop ran as it should.

However, I rebooted, and now the fan does not turn on. I walked the path from scratch (apt purged the lm-sensors and fancontrol packages &c), but now pwmconfig fails

There are no pwm-capable sensor modules installed

At this point, I just want to turn the fan on, damn the temperatures. How do I do that?

PS. The output from sensors is

coretemp-isa-0000
Adapter: ISA adapter
Core 0:       +28.0°C  (high = +105.0°C, crit = +105.0°C)
Core 1:       +28.0°C  (high = +105.0°C, crit = +105.0°C)

acpitz-virtual-0
Adapter: Virtual device
temp1:        +30.8°C  (crit = +112.0°C)

nouveau-pci-0100
Adapter: PCI adapter
GPU core:     +0.90 V  (min =  +0.90 V, max =  +1.17 V)
temp1:        +51.0°C  (high = +95.0°C, hyst =  +3.0°C)
                       (crit = +105.0°C, hyst =  +2.0°C)
                       (emerg = +110.0°C, hyst =  +5.0°C)

PPS. cpuinfo:

processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 23
model name      : Intel(R) Core(TM)2 Duo CPU     P8400  @ 2.26GHz
stepping        : 6
microcode       : 0x60f
cpu MHz         : 886.270
cache size      : 3072 KB
physical id     : 0
siblings        : 2
core id         : 0
cpu cores       : 2
apicid          : 0
initial apicid  : 0
fpu             : yes
fpu_exception   : yes
cpuid level     : 10
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good nopl cpuid aperfmperf pni dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm sse4_1 lahf_lm pti tpr_shadow vnmi flexpriority dtherm
bugs            : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf
bogomips        : 4522.14
clflush size    : 64
cache_alignment : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:

processor       : 1
vendor_id       : GenuineIntel
cpu family      : 6
model           : 23
model name      : Intel(R) Core(TM)2 Duo CPU     P8400  @ 2.26GHz
stepping        : 6
microcode       : 0x60f
cpu MHz         : 886.334
cache size      : 3072 KB
physical id     : 0
siblings        : 2
core id         : 1
cpu cores       : 2
apicid          : 1
initial apicid  : 1
fpu             : yes
fpu_exception   : yes
cpuid level     : 10
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good nopl cpuid aperfmperf pni dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm sse4_1 lahf_lm pti tpr_shadow vnmi flexpriority dtherm
bugs            : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf
bogomips        : 4522.14
clflush size    : 64
cache_alignment : 64
address sizes   : 36 bits physical, 48 bits virtual
power management: