Portable air conditioners previously running in cooling mode might take up to 5 minutes to switch over to heat mode. The unit has a safety circuit which prevents the compressor from switching too quickly and drawing excessive current.
Select Heat Mode and wait approximately 5 minutes to allow the compressor too cool down and switch to heat mode. After about 4 minutes the compressor will come on and then, after an additional 1 minute, the fan will turn on to produce warm air.