Can anyone help out with a cpl of questions?

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Can anyone help out with a cpl of questions?

Postby Tiamat1968 » Sat Mar 09, 2013 6:39 pm

Ill describe BOTH situations, and hopefully youll get back to me as quickly as you can….

#1) Customer calls with a complaint that their a/c unit isn’t cooling enough to reduce the space temp to the thermostat setting. It is running continuously running on the 3rd hot day. The thermostat has been set at 73 degrees, the house temp is 78 degrees. Air is coming out of the registers, so the filter must be clean. The air is cool, but not as cold as it should be. The air temp. should be about 55 degrees, and it is 63 degrees.
At the condensing unit the suction line is cool, but not cold. The liquid line seems extra cool. It is 90 degrees outside, and the condensing unit should be condensing at about 120 degrees. If the unit had 15 degrees of subcooling, the liquid line should be warmer than hand temp. yet it is not.
Gages are attached to check the suction pressure, which reads 95 psig, and the discharge pressure is 225 psig. The airflow is restricted to the condenser, and the head pressure gradually climbs to 250 psig, while the suction pressure rises to 110 psig. The compressor should have a current draw of 27 amps, but it is only drawing 15 amps. What is the likely problem and the recommended solution?


#2) Commercial customer calls to indicate the a/c unit in a small office bldg was running, but suddenly shut off. Tech arrives, goes to the space thermostat and finds that its set at 74, and the space temp is at 77. The fan is not running. The fan switch is moved to the ON position, but the fan motor does not start. It is determined that the control voltage supply is in the roof condensing unit on this particular installation. Electrical test instruments are taken to the roof, and the breakers appear to be in the ON position. The low voltage terminal block is mounted inside, is checked showing line voltage but no control voltage. What is the likely problem and the recommended solution?

These are questions out of a book for school, and I think know the answers, but want to check to see if im right? Its for extra credit and I want to get it! Thanxx again!
Tiamat1968
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- Can anyone help out with a cpl of *

Postby ServiceManager » Sun Apr 14, 2013 2:05 pm

For #1
There is still more info needed, air temp inside is 78 so 63 could be the right temp coming out of vents if indoor coil has got a TXV. Also just because there is are coming out of the vents does not mean the air filter is clean or that the evap coil is clean. "all stuff you need to know" I would also ck to be sure the indoor fan motor is not shutting off for a little bit and you're not knowing it, there has been a lot of issues of that with the X-13 motors, if that is not the case and all of about is clean I would clean outdoor coil then re-check sub-cool temps if there is a "TXV" at the evap coil (OR) ck you're Superheat temp if there is not a "TXV" at the indoor coil.

To be 100% sure you're freon charge is okay and could no way be causing any issues both coil's need to be clean, blower motor needs to be working at 100% blower wheel needs to be clean, air filter needs to be clean (or) new. Then check freon charge superheat "non-TXV" or sub cool "TXV" at indoor evap coil. If evap has a TXV the sub cool temp needs to be aprox 12 degrees if there is no TXV at evap coil and there is a piston or "cap tube" then you need to find out what you're indoor wet bulb temp is and you're out door dry bulb temp is at time of charging and then you can find out what the recommended superheat temp is via iPhone app "Superheat" then charge system to that temp.

After that is done you will know a lot more and can rule out a lot more if that does not fix the issue. Just remember that back in the day the rule of thumb for air temp coming out of the vents was 18 to 20 lower then the return temp but if indoor unit has a TXV on the evap coil there is know right or wrong temp coming from the vents. The TXV will open or close as need to let more or less freon into evap as needed depending on the coils latin heat load at that time.

I hope this helps,
- Dale
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- Can anyone help out with a cpl of *

Postby ServiceManager » Sun Apr 14, 2013 2:12 pm

> These are questions out of a book for school, and I think
> know the answers, but want to check to see if im * Its for extra credit
> and I want to get it! Thanxx again!

Did not see this before posting last post.... Even still this leads to a point I try to make all the time, The book does not tell you everything you need to know it just gets you started!
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