Ancient AC unit, compressor not shutting down.

[mrodgers]

Time for me to utilize some of the forum knowledge I hope. I have an ancient unit, no idea what it is. It looks a mess, it's all one unit, the air goes outside through the unit and back into a mobile home tied into the furnace duct. It runs completely separate from the furnace.

The problem, the unit does not shut off. The blower shuts down when the thermostat stops calling for air. But the compressor continues to run unless I throw the breaker.

This is what it looks like inside. Searching, I see a contactor as the typical problem and it's on modern machines and doesn't have all of this. I know enough to get me in trouble, LOL. I can dissipate the capacitor. I can pull wires off and remove components and replace them. It's not rocket science, I just don't know what the two components in the box are and which one might be the culprit. I am assuming a switch/relay is stuck, which is what searches told me, the switch in the contactor is stuck. I'm assuming the black piece on the left. And what would the other box be?

I'll have to wait until the heat has passed, especially if I just need to remove them both and take somewhere to match. I just don't know names of things in HVAC. It's all a complete clusterF of a system in a POS trailer that leaks like a sieve was suppose to be temporary. So, no, I'm not putting more money into a new system than I can sell this POS for when I'm ready to get out. I just want to toss a $20 component in instead of spending $270 on the diagnosis, $150 on the part, and $300 to have it installed.

I do have an old man out in the middle of nowhere who I can show the component to and he will get a ladder, go up on the top of a floor to ceiling shelf, go shoulder deep to the back of the shelf, and pull something out, "yup, got one right here" with no matter what f'ed up or how old the thing is you need to replace.

 

[jlv03]

Black "box" on the left with L1/T1 and L2/T2 on it is the contactor for the compressor. I suspect this is where your problem lies (compressor not turning off when cool cycle is complete). One quick thing to check, though is to remove the wire from the thermostat and see if that makes a difference. That would show if it is a thermostat or contactor problem.

The box in the middle is your 24VAC transformer. Rare for these to fail, but if it does fail you won't have any controls from your thermostat (fan or cool).

The cylinder in the bottom middle is the start/run capacitor for the compressor and outside unit fan. If those items start and run, it is probably still good.

Finally the little black box on the right is your blower motor relay. If the indoor blower turns off/on as expected, it is likely still functional.

I hope this helps.

 

[BillK]

It sounds to me like it almost has to be the contactor stuck closed. If the inside blower shuts off the thermostat is doing its job.

 

[micromind]

Another vote for the compressor contractor stuck closed (welded contacts).

Not common but it does happen occasionally, especially in older units.

 

[niget2002]

Black "box" on the left with L1/T1 and L2/T2 on it is the contactor for the compressor. I suspect this is where your problem lies (compressor not turning off when cool cycle is complete). One quick thing to check, though is to remove the wire from the thermostat and see if that makes a difference. That would show if it is a thermostat or contactor problem.

The box in the middle is your 24VAC transformer. Rare for these to fail, but if it does fail you won't have any controls from your thermostat (fan or cool).

The cylinder in the bottom middle is the start/run capacitor for the compressor and outside unit fan. If those items start and run, it is probably still good.

Finally the little black box on the right is your blower motor relay. If the indoor blower turns off/on as expected, it is likely still functional.

I hope this helps.

These are the troubleshooting steps I'd follow.

 

[firebirdparts]

Well, you're lucky, that's super easy diagnose and cheap to repair, and there's no reason that you'd buy the wrong part. That contractor is turned on by a 24v alternating current circuit of thermostat wire. Act accordingly.

 

[OccupantRJ]

That type unit is known as a package unit, and I vote that contactor is stuck. It normally will also simultaneously control the outdoor condenser fan, most likely mounted at the top of the unit. I keep a spare contactor, capacitors, control transformer, and indoor fan time delay relay in stock here. There is also a pair of jumper wires with alligator clips to use to bypass a thermostat or control wiring if needed to keep it running until a more opportune time to deal with it.

 

[The Cobbler]

The blower shuts down when the thermostat stops calling for air

I'm in the stuck contactor camp

 

[mrodgers]

Act accordingly.

Like you mean, test it for power by touching to my tongue like a 9-volt? Ha ha, sorry, I hang out at Free Parking a lot.

Black "box" on the left with L1/T1 and L2/T2 on it is the contactor for the compressor. I suspect this is where your problem lies (compressor not turning off when cool cycle is complete). One quick thing to check, though is to remove the wire from the thermostat and see if that makes a difference. That would show if it is a thermostat or contactor problem.

The box in the middle is your 24VAC transformer. Rare for these to fail, but if it does fail you won't have any controls from your thermostat (fan or cool).

The cylinder in the bottom middle is the start/run capacitor for the compressor and outside unit fan. If those items start and run, it is probably still good.

Finally the little black box on the right is your blower motor relay. If the indoor blower turns off/on as expected, it is likely still functional.

I hope this helps.

Excellent, thank you for the detailed post. Tis exactly what I was thinking. Now for it to get back to the 80's so I can turn it off and run to the store. Stores aren't open when I'm able to turn it off which is over night, LOL. This heap runs non-stop from sun up to sun down once summer really gets going. She's blowing ice cold out of the floor vents, but only holding now 77°. Gonna get warmer yet before the sun goes down.

 

[larry4406]

I also am in the stuck contactor mind set.

Look at the apparent heat damage...



OP - This is what I would do when time comes:

• Turn the stat off and blower off (main power still on), then there should not be a 24V power supply to the contactor. Then check for voltage across L2 and T2 - you will likely see 240V assuming this is a 240V unit (120V otherwise).
• Now kill the main breaker to the unit. Confirm you do not have 240V(or 120V if smaller unit) across L1-L2. Now check for continuity L1-T1 and L2-T2

The first check is intended to prove that the contactor is welded in the closed state even without a 24V applied voltage; this is why 240/120V would be present. The second check is the final coffin nail proving that there is continuity thru it without applied voltage.

 

[bonneyman]

Larry answered while I was typing. Looks discolored and burnt to me as well.

 

[fitter30]

Repair the wires that are burnt or over heated. Solid wires need to be wrapped around the screws.