BLOCKED CAPILLARY TUBE - NO PROBLEM
This will not work if the capillary tube orifice is kinked, pinched in any way to restrict the fluid flow. The capillary tube must then be replaced. One cannot always inspect all of the tube for damage so pumping the tube is the way to start. If the tube is blocked because debris has got past the filter/dryer and partially, or fully, blocked up the capillary tube there is an easy way to clear the blockage using this small modified hydraulic bottle jack. An old used jack can be used and the pump plunger "O"ring can be replaced if it is leaking. This is the second pump I have made. The first one I used to unblock about 5 or 6 capillary tubes with varying degrees of blockage and I was very pleased with it if one considers the time saved obtaining the correct tube size and then digging out the foam to replace it.
Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: Making the Capillary Pump
Unfortunately I had already made this pump when I decided to make it an Instructable so there are no images taken during the modification. This involves dismantling the reservoir, cylinder and piston section and unscrewing the cylinder and cutting the bottom 30mm off. A thick washer with a small hole is brazed to the top of the cut off piece and the brass fitting is silver soldered into the small hole. When screwing this piece back into the jack housing be careful that the ball bearing and sealing washer are both in place in the bottom of the jack housing.
The reservoir must also be shortened to make the fitting accessable but also hold a sufficient quantity of fluid to pump the capillary. I used a short length of 1/4in steel tube (for strength) with a double flare and nut to attach to the jack fitting and silver soldered a short piece of 3/16in copper to the steel pipe for attaching to the capillary tube. As you can see I have just drilled two holes in the top of the reservoir and in a piece of wood and secured the reservoir down onto the sealing rubber, and secured the pump to the wood with wire at the same time. With the right equipment a much better job could be done.
Step 2: Using the Pump
Using the pump.
The suction line must be disconnected from the compressor before pumping the capillary as you don't want any cleaning fluid getting into the compressor.
I filled the reservoir with R141b flushing fluid (I still have some) and after three pumps of the handle the resistance dropped indicating that the pipe was clear. Thinners, paraffin or meths or other fluids can be used but the evaporator must be flushed clean and dry before reconnecting to the system.
After unblocking the capillary detach the pipe from the jack and attach your flushing cylinder to clean out the the capillary and the evaporator with whatever flushing fluid you use.
Another option is, if you have have access to a diesel injector tester, then you can just make up fittings to connect to the capillary and pump it through with diesel. I haven't tried this but I had an injector tester and have no doubt that it would work.