slow leak of freon


Old 06-02-08, 07:51 AM
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slow leak of freon

Dear AC experts,

I have two, 2.5 ton carrier central AC units in my home. The split system is 8 years old. One unit works great. However, the other one has needed freon at the start of each of the last 4 summers. This unit has worked fine through each summer. However, each year, by the start of the next summer, it doesnt cool very well. The first time a repariman came, he said he added freon, tightened the connections and thought that would solve the problem. It did not. The next two times, the repairmen said I must have a slow leak but they could not find it. Each time they charged $450 for topping off the freon. In the past, the repairman, appeared to just do a visual check of the condensor. The condensor is connected to the blower by about 18 feet of pipe hidden behind a closed sheet rock ceiling. The repairman said the leak could be there.

What procedure do you recommend to diagnose this problem? What should be checked, before we cut open the ceiling to check the pipes? Is there other tests my repairman should be doing. (I have been using repairman from the same company that installed my unit originally.)

I have heard you can put a dye in the freon to help find the leak. Do you suggest that? Should we apply soapy water to the visible pipes in the condensor, evaporator and then finally the hidden pipes to find the leak?
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Old 06-02-08, 11:01 AM
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I would suggest that you stop by your local HVAC supply house and pick up a spray bottle of bubble leak detector maybe some Big Blu would work for you, there are several different brands out there and they all work very similar I am fond of the heavy bodied ones as they tend to cling better to the piping. It sounds like your leak is very small so it will most likely be hard to pinpoint. Wipe the lines off and apply the leak detector continuosly, it sometimes takes a few minutes with a real small leak for any bubbles to form so keep a sharp eye out. Suspect areas are field brazed joints/service valves/factory brazed joints and of course the dreaded coils. The bubble leak detector is ineffective at finding leaks on most coils since the actual tubing is usually encased and inaccessible to the liquid. A nice TIF Heated Pentode Electronic Refrigerant leak detector or equivalent is the most effective tool but not so sure that a 400 dollar investment is very smart for a one time use lol. You may have a splice in the lines above the ceiling that is leaking but I would check every inch of lines that are exposed before tearing into that. If you do a google search on ac coil leaks you will find a lot of interesting information they are claiming now that certain chemicals regularly found in the home can cause corrosion pinholes in the coil tubing so you may go to a lot of trouble only to find that the coil is leaking. Coil leaks are common even on units only a few years old.
Old 06-02-08, 02:19 PM
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I for sure I would have them put in some dye and see what come up. Out of the box here. But if it seem's like the freon gets out over the winter. Leak could be in the big copper return line. Kids bubble stuff works just fine. Check all line caps on schrader valves.
Old 06-02-08, 05:46 PM
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Saturn, how about hitting the enter key every once it a while in long posts, makes it easier to read.

Ed, pleasure to follow your post. Hope your son is doing well with the business.

4 years with a slow leak. Granted I don't have to pay Me for my time, but there is no "can't" find the leak.

As Ed said, have them, or a company that wants to fix rather than patch the problem, add dye to the system.

Dye mixes with oil which mixes with refrigerant. You end up with a neon sign saying "here I am" fix me.

Were I a betting man and could make money here, I'd bet on the indoor coil being the culprit.

This is what always gets me about residential, the customer is paying you to repair and maintain a system, not just keep sucking money from savings. FIX IT!
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