Expert: john t. borgman - 7/13/2009

Question
QUESTION: I believe that my unit is a heat pump, as it provides my heating and air conditioning. My question is regarding freon loss. I live in central Florida and the unit is in air conditioning mode about 90% of the time. The unit was installed in a new mobile home in 2002. There was 1 service call for a warranty repair in 2003 (not sure what the issue was then). The unit has not been serviced since then. I had an ac contractor out last week and he advised me that the unit was over 2 lbs low and needed a $350.00 service call to check for leaks and replace the lost freon. The ac rejuvenation call that the contractor was out for was to include 2 lbs of freon. The pressure readings were 180 high 50 low and he advised that the proper pressure was 220 high and 70 low.

Would you expect any freon loss over time with use in the 6-7 years since the unit was last serviced? I would think that the constant change in temperature and change from gas to liquid and back would result in a minor loss. Over the course of the years, you would expect a minor loss. The other issue is that there is no way of knowing that the previous contractor put the pressure up to the max at the time of installation.

The contractor also advised me that my capacitor was weak and wanted another $350.00 to replace it. I watched his meter and checked the specs of the cap myself and it is weak. The background here is that the contractor rescheduled my appointment at the last minute 4 times and was coming out for free to appease me. As soon as I refused the expensive repairs, he put the unit back together and put a little freon in before leaving. There was an entire checklist that he was to complete as per their advertising that was never completed.

My question is can it be possible that the freon is that low without a leak? Do you think his charges were reasonable? These charges did not include the repair of the leak, just locating and recharging.

I would appreciate any information that you can provide.
Thank You
Rick

ANSWER: Rick,
 There is no such thing as magic, a phrase from my engineering teacher of old.  Why would you think that Freon would cease to exist in the system.  Where would the loss be if not for a leak.  And pressures alone tell you nothing without the temperatures of the refrigerant at those pressures and the difference in air temperature entering and exiting the coil, both indoor and out.  Did this contractor make sure you had a clean filter and all the vents in your home open?  Dirty filter and / or vents closed will lower the suction pressure.
 The capacitor should be around 150 bucks installed.  And why do a leak search if your not going to repair it.
 If your in a mobile home you probably have only a 2 ton system or so.  Total freon would be only 5 to 7 lbs.  So if it is 2 low that is a lot.  Was it cooling?  Does the large copper insulated pipe get dripping wet after it runs for a while, with vents open and a clean filter?


---------- FOLLOW-UP ----------

QUESTION: The freon loss came from something my instructor said in my auto shop class in high school...but that was in the 70s. My experience with automotive ac (not professional) tends to lend credence to it. You still need to recharge the system now and then even if there is no leak. I was of the impression that automotive and home ac units are similar in nature when it comes to the physics of cooling.

The system is a 2 1/2 or 3 ton. The label is partially gone but I remember from previous discussions with my landlord. The filter was replaced 2 days prior, but he didn't check. As for the vents, they were all off because I had been running them through the dishwasher, but he didn't ask. He did not take any temperature readings. It was and is cooling and it does get dripping wet. When my landlord was still living here we had a lot of animals and the filter sometimes did not get changed. The unit would freeze solid when this happened and had to be defrosted with a hose. I am not sure how this would affect the unit.

It is not cooling like it used to and it seems to run too long when it is on, but the air is still cold. This is a mobile, but it is 4 bedroom and it was the largest that Fleetwood made at the time, so it is a large house to cool.

Thank You
Rick

Answer
Rick,
 You need to crawl under your home and secure the cross over duct work, it is flex duct and must be leaking.  It is the only place on a mobile home for it to leak.  Other than that....it is dripping wet when running, then no one can make it better for cooling than that.  
 And the dichlorodifluoromethane that you used in automotive A/C does not cease to exist during the refrigeration cycle, nor does it change its physical properties under the heat of compression, unless there are non condesibles in the system.  All refrigeration cycles work exactly the same with the exception of the saturation temperatures which are what dictate the temperature region they work best in.  Your teacher was wrong....look it up