Ruud A/C Stopped Working - Need advice Please

[govtdog]

This thread concerns a 10 year old Ruud UAMB-060JAZ 5 ton A/C.

A few months ago, we noticed that during the day our A/C unit was not cooling very well. Found out that our indoor coil was freezing up and we needed to defrost before we could get cold air again but only for a short time. Paid to have a tech come out and he said our unit was almost 2 lbs low on freon(holds 6 lbs). He recharged the system and it has been working as new.

Yesterday, we returned home from a 3 day trip to find that our house was hot. We had left the thermostat at 78 degrees but saw the inside temperature was at 85 and the inside blower was blowing hot air. Went outside and saw/heard that the fan and compressor were not running.
Went back inside and turned A/C to off resulting in indoor blower to stop. Waited a bit and then turned the unit back on - same result no outside fan or compressor.

Took cover off outside unit and all appears normal with no bug infestation, or loose or broken wires. Checked and reset both the breaker and the high pressure reset button. Still nothing.
Manually pushed down on contacter and bam, the compressor and fan kicked on. Tried holding the contacter down for about 3 minutes while my son checked the outflow air and the hot air got slightly cooler but not cold.. so the system may be once again low of freon? During this 3 minute operation, the top of compressor got very hot as did the small copper tube running to the outside cooling radiator coil. The bigger copper tube running to the inside cooling coil never seemed to get very cold though it was much much cooler than the smaller tube. Is that normal or possibly another side of low freon?

Hoping the problem was the thermostat, I directly connected the AC control wires bypassing the thermostat. As before, inside blower comes on but not outside fan or compressor. So, according to what I have read online, my next step is to see if the contacter is getting the 25v signal to the contacter coil from my thermostat?

Here is where I need your help, please. I have a sperry SP-10a but my use of it so far was only to measure battery power, so not sure how to set it and ESPECIALLY how to measure the voltage at the input and output of the contacter?
For example, do I turn the inside thermostat to ON before I measure the voltage? Do I need to remove the incoming wire from the contacter to measure it or do I just put the pos probe on the incoming connection and the negative probe on the outgoing (opposite side of contacter)?

- Just found these instructions online... do they look right to you?
** on the thermostat. Leave the condenser's circuit breaker off.

Inspect the conatctor's bus bar. If the bus bar depresses, the contactor's coil works. If the bus bar remains in the open position, turn a multimeter to its VAC setting. Place a multimeter probe on each of the contactor coil's wire terminals. If the multimeter reads zero, troubleshoot the air-conditioning system's low-voltage circuit. If the multimeter reads 24 to 30 volts, turn off the thermostat and check the contactor's coil for continuity.

Remove the low-voltage wires from the contactor's relay coil wire terminals. Turn the multimeter to its resistance or continuity setting. Place a multimeter lead on each relay coil wire terminal. Check the multimeter's readout screen for continuity across the relay coil. If the multimeter reads zero, replace the contactor. If the multimeter reads continuity, reconnect the low-voltage wires to the contactor's relay coil wire terminals.*/*

Other thoughts include wondering if the unit got low on freon again(due to a leak somewhere) and it caused a failure or some sort of compressor protection to initiate which is still in effect? For example, I can see and push the high pressure reset button but have no idea where the low pressure reset might be?

As you can tell, I am a relative newbie but one who must learn since I am a currently unemployed broke newbie with 2 kids and no A/C in 95 degree Texas, so any and all help is very much appreciated.

Thank you very much for your help!

[govtdog]

-
Used Multimeter and checked voltages and resistance on/to/through the contactor and it checked out fine. How can that be when it refuses to close to start the fan and compressor? The bus bar moves smoothly up and down when gently pushed with a screwdriver.

When I manually push the bus bar down the fan and compressor starts and runs... does that mean my capacitors are OK?

What should I try next?

[Freon]

If you can manually move the contactor and both the fan and compressor start then your run capacitor appears to be good. However if it appears the fan may not be running as it has before then you may have a bad run capacitor or one that's slowly failing. They are inexpensive and easy to replace yourself.

Did the tech who added the 2 pounds of R-22 find and fix the leak? If not you may be shutting down on a low R-22 safety. But I'm not sure you have the safety on the unit. In either case you need to fix the leak so you know low refrigerant isn't causing this problem.

I would pull the disconnect to the condenser (no 220 volts) and then call for cooling. Then with the multimeter check the AC voltage where the 2 smaller control wires connect to the contactor's coil. You should read 24 volts, AC and the contactor should be closed. You will hear a hum from the coil. If you do not read 24 volts at the connection points then the control wire has a break. The copper conductor can break yet the insulation stays intact. Try running your fingers over the wire and you may feel it. Check the control wires from the condenser to where the disappear into the house.

Also check the control wires at the air handler.

[govtdog]

Thanks for the help Freon!

I do have 24v at the contactor but the bus doesn't close. No humming or noise whatsoever. No problem starting both external fan and compressor if I manually push the bus down(close it).
Also checked continuity of the contractor coil and it checked out ok.
Also checked primary voltage to the contractor at both input and output and it showed 240v.

Unless there is some sort of internal safety for low pressure which stops the contractor from closing, all I can think it might be is a bad contractor which cannot be detected by checking voltages and contractor coil resistance?

I only had $200 which I could spend on the A/C when the tech came and added freon. He looked for a leak but couldn't find one where he looked outside and at easily accessible tubing inside. He said if I have a leak it is probably in the inside cold coil(don't know the real name) which is located in the air handler/blower in our attic. Although the outside AC unit was replaced 10 years ago, the inside house parts may be original and if so are 18 years old. He said that to replace the inside cooling coil it would cost around $800... and that was money I don't have, so I was hoping the recharge would get us through this summer without needing to borrow money to fix the ac.

How much freon need to be in the system for him to come and look for a leak including in the cooling coil?

Is my next step replacing the contactor for under $50 or calling a tech to come and try and find the leak for a min of $80, not including more freon?

Thanks again for any help and advice you can offer!

[Freon]

In the electrical compartment of the condenser you should find a wiring schematic. Find the contactor in that circuit and trace back to the control wires coming from the house. That's the only way to know what type of safety switch may be in the contactor circuit. You may visibly see the indoor control wires (24 volts AC) connected directly to the contactor. If you find a safety in that circuit (usually in series) turn off power to the air handler and pull the condenser disconnect. Then use a wire to jumper that safety. Now turn on the power and call for cooling. If all works you know the contactor is ok. But turn off the power and remove the jumper until you know exactly the purpose of the safety. It should be noted in the schematic. If there is no safety and the control wores are a direct connect. remove the contactor and visually inspect it closely. The coil continuity with a meter voltage (1.5 volts DC) is very different then the control voltage and that may be why it's behaving weirdly. Wiggly connections... push things around. It could be a partial short deep in the coil.

One sign of low refrigerant is ice forming on the larger copper tubing at the evaporator coil. You may be low on refrigerant but not critically low. One way to notice a leak is look for an oil stain since oil circulates with the refrigerant. That's usually easier out at the condenser. Some techs have 'sniffers' that can smell the leak as the tech moves the nose about the coils, inside and out. If the leak is in an easy to access part of the system, it can be fixed. But it won't be inexpensive since removing and replacing the refrigerant is a tedious process. A new coil should be about $300 but the labor to remove/replace is what is going to double the cost.

First find out what safety switch, if any, may be in the contactor circuit. One problem at a time.

[govtdog]

Thanks again for the help, Freon!!!

Will check along the control wires back near the air handler to see if there is anything but the wires taped to the outside of the insulation around the freon pipe.

One other thing I discovered is that it seems as though my AC has NO apparent main power disconnects. The homes breaker box is located next to the outside AC units and I do not see any separate AC disconnect such as I have seen in pictures online. I also found out that turning off the two 30amp circuit breakers marked "AC" do not turn off the main power to the primary AC but instead to the smaller 3 ton AC unit which cools the upstairs. There are two 60amp breakers which are of course unlabeled... could they be for the primary 5 ton AC circuits?

No ice on the inside coil(evaporator coil?)but of course the units been off for a few days and it is HOT in the attic. Last time before the tech came and put 2lbs of freon in the unit, there was alot of ice on the coil... so much so, that my first clue was no house cooling and not even any air flowing into the house due to the coil being totally iced up.

Anyway, thanks again for the help and I'll report what I find sometime tomorrow.

[Freon]

You need to know for certain what circuit breaker is associated with the condenser you're working on. Try turning the 60 amp breaker to off and check the voltage CAREFULLY where the line wires (large wires from the house to the condenser) attach to the contactor. Or press the contactor closed briefly with an insulated nonconducting rod and see if the compressor starts.