Need some AC system advice

[Gareth Randall]

I’m planning to completely refurb the 22-year-old AC system in my Jeep ZJ, which currently has broken blend doors in the HVAC box behind the dash. Some of the job I will do myself, some I will leave to a professional shop.

The part I will do myself is pulling the dash, removing the HVAC box and repairing the blend doors. While I’ve got the box out, I will replace the evaporator. The shop can do all the other stuff – replacing the compressor, condenser and accumulator.

Here’s my real issue: while I’m working on the HVAC box, the AC system will be open to the atmosphere. I’m not bothered about that since everything’s being replaced anyway, but once I’ve replaced the evaporator, should I reconnect it to the old components so that the car can be driven until I can get it into the shop to have the other parts replaced? Or could that potentially damage it, given that I understand nasty things happen to the inside of the AC system after it’s been opened to the atmosphere?

If I shouldn’t connect it back up to the old accumulator and compressor, is it OK to run with the lines to the evaporator disconnected? Or should I just pull all the old components and temporarily install a compressor bypass pulley?

Topic

[Its me]

I would just leave the new evaporator alone… After you re-install the evaporator I would put the protective plugs on it (it probably will come with rubber or plastic plugs for the ends)… If not then I would cap it somehow (ziplock bag with rubber bands)… The chances of something getting in it in a short time are remote, but are there…. The shop will probably want to use cleaner to clean out all the lines, so you are saving yourself the labor of hooking the lines back in and the shop the time of disconnecting them again… I would also plug those open lines that should go to the evaporator (just in case)… The system will be discharged and won’t work anyway so you will be fine…

Also the real issue with an open system is moisture getting into the accumulator… The accumulator contains desiccant which absorbs moisture… It should be the last thing bolted up and opened for a minimal amount of time (which is just installation)… When they evacuate the system (pull vacuum on it for 30-60 mins) all the moisture that got in when the system was open will be boiled away and gone…

JMHO

-Karl

[Gareth Randall]

Thanks Karl. So it’s fine to leave the new evaporator disconnected (with the lines capped) and let the compressor pulley turn even though the compressor and accumulator won’t be connected to the evap?

I’d been led to believe that if moisture got into the AC system while it was open, it would cause corrosion inside the various components. Is that the case?

[Lorrin Barth]

Moisture reacts with the refrigerant. You have no refrigerant. Moisture reacts with and uses up the desiccant. You are going to replace the desiccant. So, just do as suggested above.

[college man]

What you could do as suggested leave the new evap capped/plugged.
For the lines that are disconnected. Take small freezer zip lock bags
and put each line in there own bag. seal the bag to the line. then use
electrical tape to seal where the bag did not close or cover the ends of
the lines with either a good thick saran wrap or that plastic they use
to wrap pallets with. Then tape it with electrical tape to hold everything
in place. Then zip tye the lines secure so they don’t move.

[Lorrin Barth]

It is true that you don’t want moisture in the system. But an evaporator is manufactured, packaged and then sits on a warehouse shelf for an unknown period of time. The evaporator contains atmosphere and atmosphere contains a tiny percentage of water.

Once you conclude your work and take the vehicle to the shop, when the system is sealed but before refrigerant is introduced, a vacuum pump will be attached to the system. This is to remove air but also to removes all traces of moisture. As you go up a mountain the temperature at which water boils goes down. This is due to reduced atmospheric pressure. The same thing happens in the A/C system as the air is pumped out. Eventually the pressure gets so low that water boils at room temperature, turns to a gas and is removed by the vacuum pump.

A/C systems that contain no pressure are considered wet. If the refrigerant can leak out air with moisture can leak in. In normal operation a tiny amount of moisture can get into the system even though the system is sealed. The moisture goes right through rubber hoses. With modern hoses this is a very slow process. A desiccant is used to absorb this moisture and keep the system dry.

[Author]

Replies