Old HP nc4400 laptop on Debian, fan turns on for 10 secs, then off for 20 secs

Old HP nc4400 laptop on Debian, fan turns on for 10 secs, then off for 20 secs

I run Debian 7 on an HP nc4400 laptop. This is an old laptop with an Intel Centrino chipset. It runs fine except that the fan turns on for 10 seconds, then off for 20 seconds and then on for 10 seconds, and so on.
The BIOS doesn't say anything on ACPI or APM. dmesg | grep -i "acpi" returns this:
0317)
[    0.229900] ACPI: Dynamic OEM Table Load:
[    0.229904] ACPI: SSDT   (null) 001FB (v01 HP      Cpu0Ist 00003000 INTL 20060317)
[    0.230045] ACPI: SSDT 7f7f629b 004CB (v01 HP      Cpu0Cst 00003001 INTL 20060317)
[    0.230435] ACPI: Dynamic OEM Table Load:
[    0.230439] ACPI: SSDT   (null) 004CB (v01 HP      Cpu0Cst 00003001 INTL 20060317)
[    0.230701] ACPI: SSDT 7f7f5f53 000C8 (v01 HP      Cpu1Ist 00003000 INTL 20060317)
[    0.231101] ACPI: Dynamic OEM Table Load:
[    0.231105] ACPI: SSDT   (null) 000C8 (v01 HP      Cpu1Ist 00003000 INTL 20060317)
[    0.231211] ACPI: SSDT 7f7f6216 00085 (v01 HP      Cpu1Cst 00003000 INTL 20060317)
[    0.231603] ACPI: Dynamic OEM Table Load:
[    0.231606] ACPI: SSDT   (null) 00085 (v01 HP      Cpu1Cst 00003000 INTL 20060317)
[    0.244084] ACPI: Interpreter enabled
[    0.244100] ACPI: (supports S0 S3 S4 S5)
[    0.244121] ACPI: Using IOAPIC for interrupt routing
[    0.244789] PCI: MMCONFIG at [mem 0xf8000000-0xfbffffff] reserved in ACPI motherboard resources
[    0.245206] [Firmware Bug]: ACPI: No _BQC method, cannot determine initial brightness
[    0.260264] ACPI: Power Resource [C220] (on)
[    0.262871] ACPI: Power Resource [C228] (on)
[    0.269881] ACPI: Power Resource [C329] (off)
[    0.269959] ACPI: Power Resource [C32A] (off)
[    0.270035] ACPI: Power Resource [C32B] (off)
[    0.270113] ACPI: Power Resource [C32C] (off)
[    0.270888] ACPI: EC: GPE = 0x16, I/O: command/status = 0x66, data = 0x62
[    0.271132] ACPI: No dock devices found.
[    0.271142] PCI: Ignoring host bridge windows from ACPI; if necessary, use "pci=use_crs" and report a bug
[    0.274594] ACPI: PCI Root Bridge [C002] (domain 0000 [bus 00-ff])
[    0.283058] pci 0000:00:1f.0: quirk: [io  0x1000-0x107f] claimed by ICH6 ACPI/GPIO/TCO
[    0.285079] ACPI: PCI Interrupt Routing Table [\_SB_.C002._PRT]
[    0.285255] ACPI: PCI Interrupt Routing Table [\_SB_.C002.C098._PRT]
[    0.285357] ACPI: PCI Interrupt Routing Table [\_SB_.C002.C101._PRT]
[    0.285421] ACPI: PCI Interrupt Routing Table [\_SB_.C002.C111._PRT]
[    0.285491]  pci0000:00: Requesting ACPI _OSC control (0x1d)
[    0.285495]  pci0000:00: ACPI _OSC request failed (AE_NOT_FOUND), returned control mask: 0x1d
[    0.285498] ACPI _OSC control for PCIe not granted, disabling ASPM
[    0.298542] ACPI: PCI Interrupt Link [C10D] (IRQs *10 11)
[    0.298640] ACPI: PCI Interrupt Link [C10E] (IRQs *10 11)
[    0.298735] ACPI: PCI Interrupt Link [C10F] (IRQs 10 *11)
[    0.298829] ACPI: PCI Interrupt Link [C110] (IRQs 10 11) *5
[    0.298923] ACPI: PCI Interrupt Link [C123] (IRQs *10 11)
[    0.299016] ACPI: PCI Interrupt Link [C124] (IRQs *10 11)
[    0.299110] ACPI: PCI Interrupt Link [C125] (IRQs 10 *11)
[    0.299152] ACPI Exception: AE_NOT_FOUND, Evaluating _PRS (20110623/pci_link-184)
[    0.299282] PCI: Using ACPI for IRQ routing
[    0.306278] pnp: PnP ACPI init
[