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olgranddad 08-03-2008 02:23 PM

Lennox HS29-311-3P Air Conditioner Not Working
Hi All,

My air conditioner (Lennox HS29-311-3P)went out about a week ago and I finally have had time to look at it. This is the original A/C unit and the house was built in 1994. So it is about 14 years old. I don't know if it is worth trying to fix the current A/C unit or if I should buy a newer one to improve the SEER value.

I see the following:

I have 18.4 V and 19.7 V through the relays of the A/C unit. The 19.7V wires goes to a small cylinder. There is voltage there as I shocked myself. From the small cylinder the wires travel to a large black cylinder (condenser?). I can feel power on the fan and the "condenser" (This is my first time looking at an a/c unit. I believe the condenser is the big black cylinder inside the guard with the pipes hooked up to it. If it is called something else, please correct me). I measure 240V at the "condenser".

The fan does not turn and the "condenser" does not turn on.

I don't see any feedback from the "condenser" to the fan. Therefore, I believe that if the relays are pulled in, both should run. Both are not running.

What do I check from here?

Thank you to any who take an interest


8 Ball 08-03-2008 08:36 PM

First problem is only 19v. Should be 24v. Inspect the small wire that goes to the outdoor unit for any nicks or cuts. Is there a disconnect outdoors, and are there fuses in it? Dont understand about the small cylidrical part, larger one sounds like the compressor. Could be a capacitor.

What do you mean, when you say you can "feel" power? Have you checked your breakers? Do you mean you can hear/feel a vibration?

olgranddad 08-03-2008 09:49 PM

I'll inspect the wires closer tomorrow. Hower, the solenoid is being pulled in by the 19V. I do have 240V ac at the Condenser.

There is no outdoor disconnect. I have been shutting the main power off to the house. I have a circuit breaker panel, so there are no fuses to check.

According to the schematic I found, the small cylinder is the capacitor and the large cylinder is the condenser.

When I say I can feel power, I mean that I feel the electrical vibration at the fan and the condenser. I can also hear the hum of the ac voltage.

I am confident that I have power at the fan motor and the condenser, but neither do anything.

Thank You

8 Ball 08-04-2008 05:05 AM

Please bear with me here. If you have 24v, and 240v at the condensor, the only other thing that would prevent it from coming on would be one of the safeties trpped. Low pressure safeties reset themselves, on a Lennox the high pressure safety is a manual reset.

If I understand you correctly, the large black round thing with the pipes going to it is the compressor. The entire outdoor unit is the condensor.

Look at the piping inside the condensor, and look for a small round fixture attatched to the smaller pipes coming from the compressor. It should have a small red button in the center of it. Press the red button firmly. If the unit starts, turn the power back off and clean the condensor with a hose.
If you have had to add refrigerant to the unit in the past, you may need to again. If the charge is low enough, the low pressure safety will prevent the unit from coming on. Both of these safeties are normaly closed contacts, and can be tested with the ohm feature in your meter. If they both check out OK, you will probably need a new contactor, the large black piece with all the wires going to it.

Where are you located, the only other thing I can think of would be a fan cycle control, but we will get to that. Is this a heat pump, or just a standard split system AC unit?

You need a disconnect within 6ft of the unit.

Im gonna bet that poke from the capacitor smarted.

olgranddad 08-05-2008 07:32 PM

Sorry I couldn't respond yesterday. I had to watch the baby and couldn't get out on the a/c unit.

Ok...I am with you on the terms now.

I found the outside disconnect. It is within 6ft of the a/c unit as you stated. I opened it, found a nest of wasps, and two fuses. After killing the wasps, I checked the fuses. They are good.

I don't see where the low pressure safety limits are. I only see the relays for the fan and compressor. I assume this is what you are calling the contactor.

The wires going to the contactor are all fine. I don't see any bare wires except where the connect.

I looked at the piping of the condensor. There is a big pipe that comes from the house to the compressor and a little pipe that comes from the compressor and bends back and forth along the condensor.

I don't see a button to press anywhere. I would assume that it is right off the compressor. On the small pipe after all the bends going to the house there is a short 4 inch length of pipe that crosses the small pipe. Is this the low pressure switch? I don't see a button to press on this, but I don't know what it is. One end of the pipe seems open and the other end seems to be crimped.

Also, on the pipes between the house and the condensor, I see a knob on each that I can turn. However, I expect this to be some sort of valve to adjust flow to the compressor.

I have never had the a/c unit charged. I never knew I needed to be charged. I have owned the house since 2001, but it was built in 1994. With the shape I bought the house, I am sure it's never been recharged. Could it be that simple?

What is the difference between a heat pump and a standard a/c unit? I assume it's the standard split unit, but I'm not sure.

Thanks for the help

Yoyizit 08-05-2008 08:23 PM

I don't have a problem with 19v; these 24vac xformers have terrible regulation. Open circuit they may read 30vac.

8 Ball 08-06-2008 05:53 PM

I mean no disrespesct or offense, but it may be worthwhile to call a service company. What you have described indicates that you do not have any compressor safety devices, which is not uncommon. I cant help but think the contactor may be faulty.

Is there any way you could post a picture of the outdoor unit?

Wasps, whacked by the capacitor and a week without AC...thats gotta be tough.

olgranddad 08-09-2008 07:23 PM

6 Attachment(s)
Attached are pictures of the system. If you would like to see something else, let me know.

I'm not ready to call a pro yet, but I am getting there. I just want to make sure it's not something stupid. Like for example my sister and her furnace. The guy came in looked at it 2 minutes and changed the filter because it was clogged solid...$120.

8 Ball 08-10-2008 05:12 AM

Photo #1= capacitor(condensor fan)
#2= compressor
#3= piping at condensor coil
#4= contactor
#5= service/isolation valves

In photo #4 if you push the center of the contactor in with an insulated screwdriver, what happens? Look away when you push it in. There is a divider directly in the center, and spring loaded contacts on eighther side, the contacts are what you need to depress. Do you have 240v with one lead on the red wire, and one lead on the black wire off the top of the contactor?

In photo #5 you are showing the service valves, leave these alone. Make sure the caps are snug.

If you have never added refrigerant to it, perhaps you dont need to now. I dont see any pressure safety devices, not uncommon.

You have a "split system", not a heat pump. It needs to be cleaned. Could you move that wasps nest, kinda makes me nervous.

It looks like the compressor has been replaced at some point.

smitty8852 08-10-2008 12:55 PM

if the contactor is pulling in then and fan and compressor are humming u need a capacitor probly a 370 v 35+5 uf u can get that a a/c supplier alway make sure power is diconnected before doin anthing. capacitors hold a charge even with power off

smitty8852 08-10-2008 12:58 PM

one other thing always tap a outside disconnect with something and step away to check for wasp

olgranddad 08-11-2008 06:20 PM

"In photo #4 if you push the center of the contactor in with an insulated screwdriver, what happens?"

I went to Lowe's and looked for an "insulated screwdriver". I didn't see anything called that, but I assume that you mean a screwdriver with a rubber grip. That is what I picked up as I didn't have one. Please confirm that is what you mean before I press the contactor.

"if the contactor is pulling in then and fan and compressor are humming u need a capacitor probly a 370 v 35+5 uf "

Is there anything I can do to confirm that it is the capcitor? The contactor is definatley pulling in. I have 240V at the compressor.

"one other thing always tap a outside disconnect with something and step away to check for wasp"

That's a good common sense approach. Wish I thought of it *doh*

olgranddad 08-26-2008 08:49 PM

I just wanted to close the loop incase this thread might be of help to somebody else.

The weather cooled down and I forgot about my A/C. Then after 2 weeks it picked up again and I remembered my A/C still didn't work. I paid the price and sweated.

I looked for the capacitor on the web. It is not in production. I found the replacement cap. Most places wanted between $40 and $60 plus shipping. I wasn't going to spend $40+ unless I knew it was the problem. 3 kids, dog, wife, mortgage, will do that to you :)

After much searching I found a site called (I don't know if mentioning the site is breaking the rules. If it is, my apologies.)and picked it up for $15.50 shipping included.

Put the new cap on and the A/C was humming. Of couse the weather has cooled off again and I'm sleeping with the windows open anyway.

All of my thanks to those of you who helped me through this problem. So far this website is 2 for 2 on HVAC problems for me. You have saved me hundreds and maybe even over a thousand now by helping me DIY.:thumbsup:

InNeedOfHelp 06-23-2009 11:39 AM

Sorry to revive this thread from the dead, but I am experiencing a similar problem to the OP. What should happen when the contactor divider is pressed? My compressor starts up when it's pressed...does this indicate that my contactor is faulty? Can I just get a new one at a home improvement store, or is it a specialty item? Could it be that my thermostat isn't telling the condenser to start cooling? I'm sorry for not providing any specific details about my system (it's actually pretty similar to the OP), and if I've omitted any vital info., please let me know.

Thanks in advance for anyone who can help,

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