My Whirlpool Super Duty Imperial drier won't produce heat. I made sure the outside vent was unclogged; it is blowing cold air.

Make sure it's blowing air out the vent outside. But even though it's heating doesn't mean it's heating 100 percent so u might need a heating element. Not to expensive to buy and often not to hard to change, refer to owners Manuel or a computer on how to change it.

your heater core is possibly stopped up if there has been a radiator leak and stop leak has been poured its definetly clogged or could be a faulty thermostat

could be slightly low on charge-or cooling fan is not working-as the temp outside goes up the ac needs to be more efficent to blow cold air--and really 55 is not that cold--depending on outside conditions should be able to blow at low to mid 40 s

OK, check that the zoned heating a/c system isn't set for the passenger side to get hotter than normal air.

No airflow at all or just not cold? The AC only runs in the AC , Max or either of the defrost modes to automatically dehumidify the air to reduce fogging. The other positions vent in outside (non conditioned) air.

there should be a filter under the panel where the wipers are, also is all of your fan switch setting working?

check the filter is clear and the access vent from heater fan to tumbler is not blocked - have seen a sock blocking air flow -
drier is only a fan blowing air over a heated element & through a duct or pipe into the tumbler - on exit the air passes a filter and if this is blocked - through passage is obstructed and hot air will escape backwards

sometimes a element that heats the dryer breaks giving it only power till were it broke /then will cause no or very little heat these run about 30-34$ depending on what type of brand of dryer you have

it takes quite a while for a diesel to warm up by just idling in order to produce any heat.you have to put them under a load (drive it), before you will get any noticeable heat.if you have a block heater, plug it in 4-5 hours before you plan on driving it and that will definitely help produce interior heat quicker.

Disconnect the vent at the back of the dryer and dry a load unvented to make sure you don't have a clog in the vent line too the outside causing an air flow restriction, if still not drying check and make sure the blower wheel that circulates the heat inside the dryer isn't broken.