HELP! When I push in the contact relay the unit w

[jonmiles]

Thanks for your help.

I replaced the fan motor and double checked all my wiring again. After not finding anything else wrong my A/C seems to be working again. The problem turned out to be the high pressure switch ( which was defective before all of this started and didn't kick the button out because it was broken) and not the defrost sensor. I didn't check the wiring schematic and assumed all the sensors were closed sensors and not open so that is where I made the mistake. Then the fan just happened to go bad during this. All seems to be working now.

Hope I didn't offend anybody asking Lazypup to read my post on another forum. I didn't realize his position here.

ttyl

[LazyPup]

Jonmiles..

I am very glad to hear that your system is once again up and running.

Now in regard to having asked me to read posts in another forum. While I do believe this to be the best forum on the net, it is by far not the only forum, nor is it the only one I participate in. If and when it requires reading posts in another forum to gain the necessary information to resolve your problems, you may rest assured i did read those posts and will continue to do so.

I also want to thank you for having emailed me an additional copy of your schematic. I have copied that photo into my graphics program and enlarged it for better viewing.

Although you stated that you have already changed out the fan motor, I am not totally convinced the motor was bad. To that end, I would like to offer you information to diagnose that motor and if it proves to be okay you could retain it as a spare.

The color code for that motor is:
Black-Run winding
Brown-Start winding
Orange-Common winding.

If you have an ohm meter you can electrically test that motor.

1. Measure the resistance from Start (Brown wire) to Run (Black wire) and note the reading.
2. Measure the resistance from Start (Brown wire) to Common (Orange wire.)
3. Measure the resistance from Run (Black wire) to Common (orange wire)

Now add the values for Start to common and run to common. They should equal the value for Start to Run. If so, the motor is electrically okay.

Now to mechanically test the motor:

MOTOR BEARING TEST- First try turning the motor output shaft by hand. If it turns smooth and freely the bearings should be okay. You may see a small raised tube cast into the end bell of the motor from the shaft bearing to the outer circumference of the motor housing. There should also be a small plastic cap on the end of that tube on the outer circumference. If so, your motor has felt pads to retain oil on the bearing journals. You can pry those caps out and squirt a few drops of oil into the tubes to oil the bearings. Squirt some oil in and let the motor set an hour or so, then try rotating the shaft again. If it turns free go on to the end play test below.

END PLAY TEST- hold the motor housing firmly and try pushing and pulling the shaft in and out of the motor. You may see a bit of play in the shaft, that is called End Play. If the end play is 1/8 of an inch or less the thrust washers should be okay.

If the motor passes the above tests it should be okay and you should keep it as a spare.

I want to thank you for having participated in our forum and although I dont mean to sound as if i am wishing problems upon you, I sincerly hope you will come back again.

[jonmiles]

Lazypup, thanks once again for all of your help.

The fan motor must have been the problem because the unit ran with the fan, which it wouldn't do once the fan went bad. The unit was cooling and everything was much quieter with the new fan motor and maybe the old contactor relay was not allowing the volts to reach the compressor motor to run smoother. All I know at this point is I have double checked all the sensors and relay to make sure they work properly and added new parts where others were bad or worn and the unit is running and cooling again. I may find another problem in the near future and if so I'll attemt to troubleshoot it. But for now it's working and the defrost sensor caused me the most trouble, because it wasn't bad to start with but was a open circuit.
The parts guy tested the motor for me and said it was bad. But the motor bearings was prob. what cause it. When you try to spin the blade by hand it stops as soon as you take your hand away. The new motor will spin 20 times when pushing that hard. This = bad or dry frozen bearings. My brother works for an elec. company that sells motors and he could have purchased a replacement for me. Ready for the price, $35.00. But the parts guy had helped me out a lot with finding the problem and testing my parts so I had no problem paying the 89.00 for the motor. The blade would have cost $18.00 from my brother ranther than $35.00 from the parts place but that was my way of saying thanks for all your help. Give him the biz...

I really wanted to learn as much as possible for future issues. So the fact that I spent more on shorted transformers etc. than I had to was not a deterent. With a little help from the internet and the parts guy I was able to fix the problem and still saved a little money.

I will check the motor again the way you explained just for more experience in this field and see what I come up with.

Also if the fan motor bearings were freezing up, that may explain why the lights would dim when the A/C started up. The fan motor was pulling so many amps to start which would have led to other problems with the compressor from low available amps, right ?

I put a super boost on the HERM because the parts guy said it would help during brown outs etc. so now I won't know if the fan motor caused the lights to dim or if the super boost stopped it because once again I did 2 things at the same time and like my HPC and DS, don't know which caused it. At this point, it works.

The temps just started cooling off here so we won't need the A/C except for afternoons but I'll test it out some more and let you know how things go.

Thanks again and maybe that schematic will help you help someone else.

ttyl

[LazyPup]

Sound to me like you did a very good job of trouble shooting and you now have the problem under control.

The Super Boost you mentioned is a selfcontained start capacitor and start relay. They are excellant on older motors as they provide a bit of boost energy to get the motor up and running. The super boost helps overcome intial start up resistance that often occurs with worn motor bearings. In fact, your schematic shows an optional field wiring disgram to install a start relay and capacitor, which in your case is accomplished by the self contained "superboost".

A side note here. In a previous post you stated that you had measured the voltage on the capacitor while the motor was running, and it measured over 300 volts.

Technically speaking, voltage is properly called Electromotive Force or EMF. When a motor is running, the action of the armature spinning inside the motor windings actually generates an oppossing voltage which is called Counter Electromotive Force or CEMF. Both the applied voltage and the counter voltage are present on the capacitor while the motor is running, which explains why motor capacitors have a maximum voltage rating that is nearly double the applied voltage. (appied voltage is 250 volts but the capacitors are rated 370v.)

[jonmiles]

The Fan terminal and the HERM terminal both read the same exact volts of around 390 when the unit was running. After the fan stopped working the HERM dropped to like 340 and the Fan was 88 with COM at 240. If the compressor was running and feeding back why did the HERM drop to 340 ? I expected the FAN to drop when not working but not that much, which is why I had the capacitor checked. I didn't take any readings since starting the unit back up last night because it was late and raining. Don't really like working around elec. with water running off the roof on my head. Even when the power is off, so I decided to wait till another day for more readings as to what is showing what.

ttyl

[LazyPup]

Due to the erratic nature of CEMF it is nearly impossible to test a capacitor by taking operational voltage tests.

There are specific capacitor testers on the market that can measure the actual microfarad rating of an unknown capacitor but they are rather expensive and seldom used.

You could also take an actual operational reading using an oscillocope, but scopes are very expensive and require considerable training to understand the sine wave display.

Although you do occassionally find a capacitor that breaks down under load, that is very rare. For the most part, if a capacitor will pass a simple static resistance test it can be assumed to be okay.

A word of caution before we begin testing capacitors. Capacitors can store a tremendious charge of energy for days after they are removed from a circuit. NEVER TOUCH THE TERMINALS ON A CAPACITOR UNLESS YOU HAVE DISCHARGED IT FIRST.

To discharge the capacitor, first turn the unit off and pull the service disconnect.

Test the voltage across the contactor to insure their is no supply voltage to the unit.

The technically precise method of discharging a capacitor is to connect a large value resistor across the terminals to bleed off the stored charge, but in the field we seldom have a suitable resistor so they are often discharged by touching the tip of a heavy screwdriver across the terminals. Make absolutely sure the screwdriver you are using has a good insulated handle.
It is also an old electricians trick to put one hand in your pocket while performing the test with the other hand. That may sound silly, but when you get a spark it is an instinct to grab at what your working on. Keeping the free hand in your pocket will retard the reactionary function and could prevent you from injury.

Once you are sure the capacitor has been discharged, remove the wires from the capacitor terminals.

Using an analog type (Needle indicating type, Not digital.) OHM Meter set on the highest resistance scale, touch one probe on each terminal of the capacitor. You should see a quick deflection of the needle upscale, then slowly fall back to zero. Reverse the probes on the terminals and you should see the same reaction again. If so, that is a good capacitor.

If the needle does not move, the capacitor is open. (Replace the capacitor)

If the needle moves to full scale and holds the capacitor is shorted. (Replace the capacitor.)

When the test is done, replace the wires and install the rubber grommet cap over the capacitor terminals.

When replacing a capacitor it is vitally important that it be secured in place. Some people make the mistake of just attaching the wires, replacing the grommet cap and laying the capaitor in the control section. If it should happen to move from vibration while the machine is running it could cause severe damage to the AC unit.

[jonmiles]

Example to think about:
That's what the guy told me where I bought the parts. When he used a digital meter he said if you set it on tone and get one beep it is good. If you get two beeps it is bad. If you don't get a beep it is bad. Problem is, if you don't make sure the terminals are very clean and switch the prob. back and forth you may not hear a beep. My meter did not beep but his expensive meter did. So it also depends on the meter you use. Could be the batteries ? I don't know for sure. His beeped and mine did not testing the same capacitor. I know the capacitor works because it's in my working unit now. hmmmmm

Thanks for the tip thought Lazypup

[LazyPup]

Most digital multimeters have a minor computer circuit that uses a sampling technique processed over a short period of time to obtain their readings. The end result is that they are capable of much more precise measurements than the common mechanical scale analog meter.

However, when servicing motor circuits in most cases you do not require a finite volatage measurement, but often require the quick response capability of the analog meter to check start voltage surge or drops or when performing a test on capacitors.

With that in mind, many of the test instruments used by electricians, HVAC techs, appliance techs and motor techs have both a digital display and and anolog display function.

Some have a digital bar graph on the bottom of the display while others have both an analog needle movement and a digital display.

In many cases the preferred instrument for testing motor circuits is a Snap On Ampmeter. Most snap on ampmeters also have voltagee and resistance measuring capabilities, which makes it a full service instrument for working motor circuits.

[jonmiles]

After allowing the A/C to run for a week now everything is still working fine again.

I wanted to say Thanks Again to Lazypup for all of your help with troubleshooting this problem. I couldn't have done it without people like yourself pointing the way.

Lots of luck with your next troubleshooting job.

Thank You

Jon

[LazyPup]

Jonmiles,,,,,
I wish to thank you for participating in our forum as well.

I think i can speak for all the tradesmen who participate in these forums when I say that you the homeowners and DIY'ers offer a lot to us as well.

In all service work proper diagnostics is critical. Any trained technician can tell you that working hands on, with all the proper diagnostic tools at hand will yeald a fair analasys of the problem, but analyzing problems sight unseen with little more than the written word, and bits a pieces of data collected by untrained amatuers will definitely sharpen our theory and diagnostic skills. In fact, I often print out the posts and use them as quiz material in our apprenticeship program. For that we thank you.

[HayZee518]

Digital meters are good but have their p[lace. Nothing will EVER replace a good 'ol Triplett analog v-o-m. I have one I've had for like 30 years ---