You mentioned the "heater/defrost unit" which implies the complete heater box under the dash. There is no reason to remove that complete assembly. Instead, you repair what is wrong with that. The compressor does not have to be removed to prevent the AC system from running, but someone may have replaced it with an idler pulley if the clutch had failed. It sounds like you had two unrelated problems. That is not very likely.
If the compressor was removed, most people just let the hoses hang there, which is a real bad idea. When air gets into the system, the humidity comes along with it. That leads to corrosion of metal parts and typically results in a lot of additional failing parts when you try to resurrect the system. At a minimum, every AC repair job that includes replacing a part that carries refrigerant, requires the system be pumped into a vacuum for at least half an hour. In a vacuum, water boils at seventy seven degrees and turns into a vapor that can be drawn out before the refrigerant is pumped in.
With this type of job, it is standard procedure to replace the receiver/drier. That unit has a desiccant in it to absorb a few drops of remaining water, and a filter. The condenser and evaporator are made of aluminum, as well as some of the hoses. You can expect them to develop corrosion that will flake off and hopefully make it through the compressor to the filter where it will be trapped. If a flake gets through the filter, it will usually become lodged in the orifice that controls how much refrigerant flows into the evaporator. That will cause a failure to cool, or it will cool intermittently. It is common to never achieve the same level of efficiency as with a system that was never left open.
The people at a repair shop will inspect your system, then come up with a repair estimate. It is unlikely they will include a warranty on anything other than what they replaced. There are likely to be additional or recurring problems that they have no way of knowing or preparing for. It is not fair to expect them to warranty things they have no control over. A lot of shops will not even try to put an AC system back in service if it has been open to air, because they know it is only going to lead to dissatisfaction on your part.
Sunday, March 12th, 2017 AT 1:39 PM