We request 9.1hrs to obtain IRAC photometry of 11 cold brown dwarfs. The observations will complete the dataset of near-infrared spectroscopy and 1-5um photometry, for known brown dwarfs with spectral types >T7, and temperatures of 500K to 800K. These rare very late- type T dwarfs are the coolest objects known outside of the solar system. For these the [3.6] band samples a low-flux region of strong CH4 absorption, and the [4.5] band a bright region subject to absorption by dredged-up CO. The [4.5] flux becomes increasingly dominant at low temperatures, and is the best temperature indicator for the latest T dwarfs, for which the near- infrared features are saturated. Combining accurate IRAC photometry with our near-infrared data, and models, will allow us to constrain temperature, metallicity and gravity, as well as vertical mixing in the atmospheres of our targets. Now that objects as cool as ~500K are being found it is vital that we understand their behaviour in the mid-infrared, especially in the WISE era, when the red [3.6]-[4.5] color will be used to find even more extreme objects.