Btu Buddy 170: Routine Air Conditioning Call, No Cooling
Bob and Tim just arrived at the house of a new customer. The customer explained to them that he just started up his air conditioner for the first time this spring. There was a warm spell, and the system didn’t work. As a matter of fact, it didn’t cool — the outdoor unit did not run at all.
Bob explained to the customer that they would get started looking at the system and figure out what was going on.
They went into the house and set the thermostat to 75°F when the house temperature was 80°, so the unit would try to start up. They heard the indoor fan start, so they knew that the control voltage circuit was working correctly. “I think we need to move outside and make sure the 24-V signal is reaching the outdoor unit,” Bob said.
They removed the control panel cover, and Tim checked the voltage from the Y wire to the common terminal. “There’s a 24-V signal calling for cooling, but the compressor nor the fan are running. The compressor contactor is not engaged,” Tim reported.
“Check the voltage across the low charge protection control. It’s on the liquid line,” Bob said (Figure 1).
“I read 24 V across the control contacts, so that means the control circuit is open at this point,” said Tim. “This is one thing at least that is keeping the unit from starting. Please explain to me the low charge protection of this unit.”
“The low charge protection control is virtually a low pressure control (Figure 2) that opens on a drop in pressure or makes on a rise in pressure. The control is placed on the liquid line in the condensing unit, and when the charge reaches the preset point, it stops the unit from running. When the low charge protection shuts the unit off, it’s usually a sign of no charge at all in the system. If there is a large low pressure side leak, it will prevent the system from operating in a vacuum and pulling atmosphere into the system,” said Time. “Get the gauge manifold, and let’s see how much pressure there is in the system. I am betting there is no pressure.”
They fastened the gauges to the system and, sure enough, the high and the low pressure gauges both read zero psig.
Tim knew just what to do — he went to the truck and got the nitrogen cylinder and an R-22 cylinder of refrigerant. He put just a small amount of R-22 in the system to use as a trace refrigerant and then pressured the whole system up to 150 psig. Then he said, “Let’s go listening before we get out the leak detector. If the system is all the way out of refrigerant, we might be able to hear the leak.”
They listened to the outdoor unit carefully and did not detect any sound, so they crawled under the house where the tubing ran towards the air handler, which was in an upstairs closet. As they were crawling down the route, Tim said, “I hear a hissing sound. We need to look closer at the tubing.” They started looking at every foot of the tubing, and they found a place where it came through the brick wall and the liquid line had a sharp bend in it. They used soap bubbles and verified there was a leak.
“I will let the pressure out of the system, and we will need to cut the tubing and put a coupling in this place,” said Tim.
“We also need to install a filter dryer (Figure 3) in the liquid line,” Bob added.
“It seems like the system was sealed — it only has a pinhole in it. Why should we have to do an evacuation and install a filter dryer?” Tim asked.
“We have no idea how long the pinhole has been in the line. A system like this will breathe over time as the temperature of the system warms and cools — the vapor inside the system expands and contracts, pulling in small amounts of air and then exhausting them when it heats up. The temperature difference from day to night, season to season will bring enough contamination to the system to cause problems. So, we correct these problems by pulling out any atmosphere that was in and filtering the system on startup and while it’s running just to be sure that we have a good, dry system. Remember that air contains moisture and oxygen. These two products will set up corrosion within the system over time, shortening the life of the system,” Bob said.
They got set up with their torch and cut in a coupling where the leak had been. They then cut a liquid line filter dryer into the liquid line, soldered everything back together, and were ready to do a pressure check. They only had two places to check — the two connections on the coupling and both ends of the dryer. So, they got the system pressure back up with a little bit of trace refrigerant, R-22, and nitrogen. They pushed the system pressure up to 150 psig and checked it with the electronic leak detector. Everything was solid, so they installed the vacuum pump and started it operating.
“We probably have 45 minutes while the system vacuum pulls down. Let’s use this time to do a complete check of the system because we have nothing else to do,” said Bob.
They checked the outdoor fan motor and oiled it, cleaned the outdoor coil, changed the indoor filter, and oiled the indoor fan motor. Meanwhile they checked the indoor coil to make sure that it was not dirty, which it wasn’t. It was now time to charge the system and start it up.
They went to the customer and explained what all they had done after they had charged and started the system and checked it for the correct charge. The customer was impressed with their professionalism on the job and he ask Bob for advice for his system. “Most people who take good care of their system have an annual service contract that checks and cleans the coil if needed like we did, checks the motors, and operates the system to make sure that it is operating at full efficiency,” said Bob.
The customer agreed that he would be doing that with their company from now on.
As they were riding away from the job, Bob explained to Tim, that’s how you get new customers — by doing a good job showing them what you do and then signing them up for long-term business. They will probably be with the company now for years because we did the right thing with the system and provided them great service.
Publication date: 05/20/2017