Tempature Control valve


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Old 06-08-11, 08:21 AM
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Tempature Control valve

What is the running price to replace a tempature control valve? It seems like a fairly easy valve to replace, is this something I could purchase online somewhere and replace myself?
 
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Old 06-08-11, 09:59 AM
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You are going to have to be more specific, what kind of machine and what exactly are you calling a "tempature valve". If you are referring to an expansion valve then the answer is no, you cannot replace it yourself and quite possibly not even purchase it.
 
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Old 06-08-11, 12:39 PM
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thanks for the response Furd...Im speaking about the AC unit in my house. Its a Lennox Central heat and air unit. It seems to blow cold for about an hour or so and then just blows warm air. I had a friend look at it and they stated that the tempature control valve is not opening and closing like it should and needs to be replaced. I was wondering if that part is something that I can purchase myself and replace?
 
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Old 06-08-11, 02:53 PM
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I still don't know what you are referring to and I doubt that your friend knows either. Refrigeration systems (your air conditioner is just a big refrigerator) use what is called an expansion valve to allow a controlled amount of liquid refrigerant from a high pressure supply into a coil of tubing called an evaporator. The evaporator is located in the duct of the furnace and when the high pressure liquid refrigerant "expands" into the evaporator the refrigerant absorbs heat and changes to a low pressure gas. The heat to cause this evaporation comes from the air flowing through the evaporator coil inside the ductwork and passes into your home's living quarters.

Once changed to a low pressure gas the refrigerant then travels to the compressor where it is changed to a high pressure (and hot) gas. This gas travels to another coil, called the condenser, where the outside air cools the hot gas and it condenses to a liquid at high pressure and the cycle starts all over. The compressor and condenser coil are located in the outside cabinet.

The ONLY "temperature" (the correct spelling) valve in the system is the "thermal expansion valve" that controls the amount (not temperature) of liquid refrigerant passing into the evaporator. It is part of the sealed refrigerant system and CANNOT be serviced except by a person that has taken qualifying tests and certified by the United States Environmental Protection Agency. Most companies that would sell this valve won't even sell it except to a person holding the EPA certification.

Now what you CAN do is to do some simple tests to make a preliminary determination of the problem. Shortly after starting the A/C hold your hand on the larger of the two copper tubes connected to the evaporator (the coil in the duct at the furnace) and feel the temperature. It should be cooler than the room temperature and will eventually get quite cold. It may get covered with moisture if the humidity is high but it should NEVER get covered with ice. The smaller tube should be slightly warmer than the outside air temperature at all times.

After an hour or when the temperature coming from the room air registers seems to be warming up do the "feel test" on the tubes again. If you have an access panel that will allow you to see the evaporator coil in the duct open it and look for ice on the coil. Any ice is bad and usually denotes a low refrigerant charge. The same rules apply on recharging a refrigerant system as do repairing or replacing the expansion valve. Partially because of the requirement for certification and mostly because it is not as simple as it looks the cost for adding refrigerant or changing any part of the refrigerant system is fairly high. Most companies are going to be charging in the neighborhood of $100 per hour plus the cost of parts and supplies. Larger cities are going to have higher prices than smaller cities.

Please post back with the results of the simple tests I described. And first of all, make sure that the filter(s) in the air ducts are clean.
 
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Old 06-10-11, 07:37 AM
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Sorry for the confusion as I misunderstood what I was told and it is in fact the thermal expansion valve. There are no indications of ice on any of the coils just moisture. The filters are clean as well as I replaced them not long ago.

I understand that its best to have a certified tech look at the unit but dont have the money. Obviously, that would be the ideal situation but am merly trying to work within my restraints. I was simply wondering if I could either purchase the valve and have a tech replace it or do it myself?
 
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Old 06-10-11, 09:05 AM
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And I'm sorry to be a broken record but no, you can not repair this yourself. My area of expertise is with commercial air conditioning systems but the principles are the same as are the laws. To change the expansion valve you would first need to "recover" the refrigerant in the system and that takes specialized equipment and training. Depending on how the present valve is installed you may need to have a torch and brazing skills to replace it. You would need to purge the system with dry nitrogen while brazing to protect the interior of the copper tubing. After the valve is installed the system needs to be pressurized with nitrogen to test for leaks and if any are found those leaks need to be repaired.

Then a vacuum pump would be connected to the system and a deep vacuum drawn to remove any moisture that may have entered during the valve replacement. After this vacuum treatment the vacuum would be "broken" by admitting a small amount of the dry nitrogen and then a new "filter-dryer" cartridge installed with another leak test. Finally the refrigerant is re-installed and temperatures and pressures at various points of the system are checked and adjusted.

As you can now understand, the equipment for all of this will likely cost upwards of ten thousand dollars and the skills required are considerable. Even if you could purchase the valve (which is doubtful) you cannot purchase refrigerant or all of the tools necessary without first having the EPA certification. The skills necessary cannot be learned from reading a book, Internet forum or Wikipedia entry. I'm sorry for your financial status and wish there was something good I could tell you.
 
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Old 06-10-11, 09:12 AM
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understood and thanks for your time, I appreciate the assistance!
 
 

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