A/C Problem in Houston

Problems related to residential installations.

A/C Problem in Houston

Postby Noble » Tue Aug 02, 2011 8:27 pm

As a bit of background information I have a new-ish townhouse constructed in 08, i have a rheem condenser unit outside and central air/heating with a central filter.

This past Thursday i woke up at about 8am with a lower layer of cool air and a layer of warm air on top of it, as the A/C system was on over night and apparently the condenser fan had stopped running. I called an a/c tech and on friday after a brief diagnosis he stated that a capacitor was at fault and replacing it would restore cooling. I did not see him check the refrigerant pressures on that visit, nor did he attempt to verify a repair by checking the inlet/outlet temperature differences. He was correct- the capacitor did restore the fan operation, however cooling was not restored. He did not leave the bad capacitor and i did not request the part.
I called saturday explained the situation and that i would like a full inspection of the cooling system, to the same company, and monday the tech arrived and informed me that the problem was the contactor was going out and the compressor was not receiving enough electrical power to properly operate, after replacing the contactor, he claimed to put gauges on the system and stated it required refrigerant and proceeded to add it to the system, I requested that he look over the system to ensure that it would operate properly, after his inspection he stated that i needed to replace my filter and other than that the system should operate as expected. After he left I purchased and installed a new filter. The lowest temperature the house hit last night was about 90*
- Shouldn't a contactor be part of the electrical system diagnosis, during which he decided to replace the capacitor?
Last night i was google-ing around and found this forum and its wonderful articles, after reading a bit and refreshing myself on hvac systems(i'm an auto mechanic, however most of the A/C work i do is simply evacuation and removal of systems for 'performance gains'/clearence issues for turbo kits) And after some poking around i discovered that the while there is some pitting/burning on the points (and that is reason to replace it on preventative maintenance) none of the resistance readings were out of spec, from the materials i was reading, ~.1 ohm across contacts when closed and the coil was at about 25 ohms. The Suction line is of ambient temperature, and the discharge/liquid line is also of ambient temperature, from my understanding the suction line should be 50-55* and the discharge/liquid line warm/hot to the touch.
Today, again i called the A/C company and explained that the previous repairs did not restore cooling and that the inspection and verification the tech gave me was not accurate. She apologized and promised to make it right, so again the tech came out and i pointed out the lack of a difference of temperature in the lines, as well as the obvious lack of cooling, and asked if it could be an issue with the compressor or if it might possibly be the expansion valve. He put gauges on it and stated that the low side was unusually low on pressure, reading in at about ~35lbs, and the high side was reading about 225, and stated that the low side should be 70 and the high side 250 and that it was probably the expansion valve, he stated that he 'adjusted it' and though it would need to be replaced it should cool through the night. He checked his gauges again and they read 70/250, again he stated that it will cool through the night but the expansion valve will need to be replaced. There has been no change in cooling what so ever. The suction line is still ambient temperature as well as the liquid/discharge line.
After reading the techs posting here i did not see him checking a single vent or return with a digital thermometer nor has he stuck around long enough to verify proper cooling. I have since called and setup an appointment with another company, however i'm looking for any kind of advice as to what this issue can be, i feel like this tech keeps throwing parts at the problem hoping it will fix it- that is not in my opinion proper diagnosis. Any input/opinions would be greatly appreciated.
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- A/C Problem in Houston

Postby heatseeker » Fri Aug 05, 2011 11:52 am

Good response, I'm kind of in the middle myself half parts changer and half technician. I will never stop learning some days are very challenging.
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- A/C Problem in Houston

Postby Freon » Sat Aug 06, 2011 1:49 pm

If this system has been running fine for years and the tech did not open it up, I am puzzled how the expansion valve can become clogged. I would go back out and find the condenser schematic, usually in the electrical compartment of the unit, and verify the tech used the correct capacitor. Each condenser has very specific microfarad values for their fan and compressor run capacitors. Deviating from that value can cause problems. Did he replace the capacitor with a dual capacitor (one capacitor each for the fan and compressor both contained in one "can" with 3 connections at the top) or did he replace a single capacitor... you'd see 2 "cans"?

Out of curiosity, could you post the make and model and age. Also when the condenser unit is running, carefully feel the smaller copper line and see if it feels hot... be careful it may be very hot. Then check the bigger copper line and see if it feels 'beer can cool". Althought not the correct way, it will tell me if the condenser is doing close to what it should be doing. Also tell me if you see, in series with the smaller copper line, a cylinder shaped object about 3" in diameter and 5"long.

Since the unit was cooling fine until the fan capacitor broke, it should cool fine now with the correct capacitor. The only other thing the tech did was add refrigerant and he may have messed that up. What else is there that he did?
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- A/C Problem in Houston

Postby nomadpeo » Wed Aug 10, 2011 7:02 am

another 'tech' without training. common problem. changing companies is your best option at this point. temperature readings of the lines and calculation of superheat and subcooling will tell the story.
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