measuring subcool using webcontrol

[fwd03]

I had an A/C technician came to tune the air condition for me. However, he came and did not do anything, but wanted me to replace the working air condition to a new model, with my current A/C total working hour is less than 1000. The only problem is not cool enough. I let him go.

I want to check out how air conditioning unit working myself. My first goal is to measure the subcool, because the A/C compressor labled sbucool 15F. I brought the pressure gauge meter. But I don't want to buy the thermometer for A/C technician, since I don't want to be A/C technician, just want to check out the subcool, then ask A/C technician to add coolant if needed.

I checked with manufacture of DS18B20, they told me the sensor actually using its ground pin to sample temprature. I want to use webcontrol and DS18B20 to measure the pipe temperature. I wonder how can I make the best thermo contact between ground pin and A/C high pressure copper pipe? Just tape it to the pipe? Could ground pin directly touch the copper pipe causing damage to webcontrol?

 

[tmbrown97]

I won't get started on what I think of most HVAC technicians... luckily I finally found a good one that fixed my unit for $450, when everyone else wanted between $4500-$9000 to replace everything...

The most basic test of all, is to put one hand on the larger copper pipe and one hand over the fan. The copper pipe should feel about mid 30's - like a cold beer is the analogy the HVAC guys used... and the air out the top should feel like it's about 100 degrees - a nice noticeably warm temperature.

I also suggest calling around and look for the smaller HVAC shops - they tend to be fixers - the larger firms employ a bunch of lower-level HVAC technicians who are on commission to try to sell you everything imaginable.

A friend of mine had a compressor die last week - wouldn't wait for my trusted guy to show up... was told the entire system was shot. Price - $7500 - so they worked out financing and had the unit replaced 24 hours later. When I calculated the payment out, after financing, they'll pay $18,000 - when all they really had to have was a $3K compressor. I really don't like HVAC people!

 

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I just put the DS18B20 sensor on the copper pipe on the high pressure side, using some old fabric to wrape around as insulation. Webcontrol reads about 90F. The pressure reading is 230psi, checked the liquid pressure/temperature conversion chart from Fluke site showing about 110F. The panel on the AC unit saying TVX subcool 17F. If I deduct 17 from 110, that is 93F. So that actual liqud temperature is 3 degree cooler than required subcool. I don't need coolant. Probably I just need to replace filter.

After I told that HVAC technician that I did not want him do anything, before he was leaving, he said that he could add 6lbs coolant to my A/C at $200 per lb. Now I know I don't need adding any coolant. Actually, since subcool is lower than spec 17F, it has slightly more coolant. Too much coolant would kill comrpessor. If I let that HVAC technician add 6lbs coolant to my AC unit, I will probably need new compressor next week.