Air Conditioner / Heat Pump Contactor Relay Q&A

Air conditioner & heat pump Contactor Relay FAQs
MultiAqua chilled water fan coil system installation

HVAC Contactor Relay Damage Diagnosis & Repair FAQs

Helpful diagnostics involving HVAC contact relays are at

CONTACTOR RELAY DIAGNOSIS & REPAIR

and at

COMPRESSOR START RELAY DOESN'T CLOSE

13 y.o. Rheem heat pump relay contacts keep burning or welding

I have a 5 ton Rheem heat pump/ac system that is 13 years old. About 9 months ago it started burning and welding the contacts on the in the condensing unit about every 3 to 4 months. The thermostat would turn off the air handler but the condensing unit would keep running and ice up the suction line back to the evaporator coil.

At this time the heat pump operation is fine. I'm sure there is an answer to this problem. Any help you can provide will certainly be appreciated.

Thanks for your time and advice. I have contacted three techs.and gotten the following answers: I don't know - - You may need to install a hot start device - - you may a have a fire ant problem. Rather than pay one of these techs to come out, I did the following to keep from buying contactors.

I installed a 3 phase 40 amp relay to split the compressor load current to make it thru the winter. It is working fine now.

I will soon remove this relay and inspect the contacts. I realize this is probably only a band-aid approach, however will try for a different tech later this year. Also, would like an explanation of how to check out the control board. Again thank you for your time and diagnosis. On 2019-01-04 by Daunne

Reply by (mod) - 13 y.o. Rheem heat pump contacts keep burning or welding

Daunne

Well my goodness!

Shown here: SUPCO A/C or heat pump temperature sensor used to detect freezing conditions or coil icing. Opens at 35 degF to permit the compressor motor to run at safe outdoor temperatures.

More on why an air conditioner's compressor / condenser unit might be burning up or welding contactor or relay component

I most-respect the tech who answered "I don't know" rather than making up an explanation or offering to just throw money at the unit.

What's disappointing is getting answers without the slightest effort at inspecting and troubleshooting the unit. NOBODY can give a completely-reliable answer to your AC unit welding contacts over the telephone.

What's wanted is an on-site inspection by an experienced HVACR technician.

Call an established service company,

ask to speak with the service manager, and politely explain that you've been getting lots of opinions and no help,

and that you would be grateful for and glad to pay for an inspection and diagnosis and repair by one of their senior, experienced technicians.

Fire Ants Causing Trouble in the A/C Compressor Unit?

Regarding the fire ant in the air conditioner problem, yes it's true that fire ants sometimes nest in outdoor compressor/condenser units AND it's possible that insects can invade and short circuit or damage electrical components.

Most likely, even a moderately-careful visual inspection will tell you - or your senior technician - whether or not there are ants or other invaders inside the compressor/condenser unit. Look for ants, an ant mound of debris, insect fragments.

If you find an ant invasion the unit can be cleaned - often simply by hosing it off, taking care not to soak electrical components.

If the ant invasion in your air conditioner unit is extensive or recurrent you'd get help from a pest control expert who will apply an appropriate pesticide around the unit and elsewhere if needed.

More details about fire ants and their control is in this

U.S. USDA IMPORTED FIRE ANT IDENTIFICATION & CONTROL MANUAL [PDF] retrieved 2019/01/06 original source: US Department of Agriculture, USDA, www.aphis.usda.gov/import_export/plants/manuals/domestic/downloads/fire_ant.pdf

The manual does not discuss invasion of air conditioners but does give help identifying and controlling imported fire ants.

Hard Start Motor causing Welded Relay Contacts?

About installing a "hot start" device, most likely referring to a hard-start capacitor, that's not an unreasonable guess but some additional explanation, in which I am GUESSING at what that service tech was thinking, would have been helpful to both of us.

I suspect she was thinking the following: if a compressor motor is faililng and having trouble starting, we can add a hard-start capacitor that gives it an extra high voltage kick to get the motor going.

A hard start motor can sometimes draw high current that in turn might burn a contactor or switch.

However if a compressor motor is failing, while adding a hard-start capacitor may keep it running for a time, we ought to realise that we may have to replace a failed compressor motor ($$$) soon.

Details are at

CAUSES of HARD STARTING ELECTRIC MOTORS inspectapedia.com/electric/Motor_Hard_Start_Causes.php

and at

CAPACITORS for HARD STARTING MOTORS inspectapedia.com/electric/Starting_Capacitors.php

Checking out the A/C Control Board

Start with a visual inspection for signs of overheating: burn marks, melting components

If you are qualified, trained, and can do so without getting shocked or killed, you would check the current draw of the unit when the A/C motor is trying to start up.

What causes an A/C relay contactor to refuse to switch "ON"?

What is the cause of relay contact switch not coming on. It is new part, Could it be low on refrigerant? - On 2020-09-08 by Nabi

Reply by (mod) - Check for a loose wire, bad control board, improper wiring

Difficult to answer because I'm not sure which relay is giving you trouble. It could be an improper wiring problem or a control board problem or even wrong relay.

Unless yours A/C system sports extra controsl not normally found on residential cooling units, low refrigerant won't prevent the system from running - at least not until the compressor is damaged.

Contractor relay engages but condenser fan motor does not turn

I myself have the same issue my contractor does engage but my new condenser fan motor does not turn on the contactor is pushed in but nothing - On 2020-09-29 by Michael moreno -

Reply by (mod) -

Still that could be badly-burned contactor points that just make no electrical contact.

A service tech will check for power at the control board.

See the diagnostics at AIR CONDITIONER WON'T START - home; be sure to review that article.

A/C or Heat Pump Won't Start, Contactor Relay FAQs

Air Conditioner or Heat Pump won't start: Contactors won't pull in when they should

New package system a/s 10 ton first stage of cooling works perfectly when both stages of cooling are called for contactors will noy pull completly in .Yes good ground,208 330 yes 24 volts at transformer Trane has no clue.

A/c contractors have no clue .

Installed new Honeywell thermostat inside packaged unit at factory wiri.

Yes I changed the transformer yes have changed both contactors.

Yet there is a matching unit next to this one both wired same other unit runs perfectly.

Im at a total loss 30yrs exper s.O.S. Mp#3 954 -803- 1646 - On 2012-07-26 by Anonymous

by Coastal HVAC: If a Contactor is Not Pulling-In when it Should, Measure the voltage at the contactor

Have you measured the voltage at the contactor?

(Not at the transformer) With the contactor not pulling all the way in, it sounds like you don't have 24 VAC at the contactor.

If this is the case,:

Check the connections between the transformer and contactor for a resistance joint.

Could be a wire-nut connection or the t-stat resistance (either via a relay or a collector feed). - by Coastal - HVAC Repair Company

Reply by (mod) - a bad connector or on occasion a partial short or leak in the low voltage wiring could drop the voltage at the contactor.

Coastal, thanks for that excellent suggestion made to Anon. It makes sense to me too that a bad connector or on occasion a partial short or leak in the low voltage wiring could drop the voltage at the contactor.

More diagnostics are

at COMPRESSOR START RELAY DOESN'T CLOSE

Daniel

Manually Pushing the Contactor Relay Indicates Pending Outdoor Compressor Failure?

I could manually push in the contactor relay to start the compressor and fan manually.

Last week, I woke up to the indoor temperature a few degrees high. Warm air was blowing in.

I went to my outside unit and the fan was not running.

I replaced the capacitor and it worked.

But the air conditioning couldn't keep up at night.

During the day when it was around 99 my home was nice around 76 but at night around 81.

Yesterday the compressor was not running. It was getting power.

Today, I put in a hard start kit and it worked. But about five hours later the compressor was not running, just the outdoor unit fan.

I pulled the power and when I powered up again, even the fan and compressor did not start.

Multimeter showed me around 25V on the two lines coming from indoors on two sides of my contactor (and 120 V on the other two connections).

One of the 25V lines connected to the two sensors on the refrigerant lines. But the contactor didn't engage.

I could manually push in the single button to start the compressor and fan manually.

What would cause three different issues within one week? I plan to replace the contactor tomorrow. Another night of muggy 90+. - On 2011-07-09 by Jeremy -

Condenser fan runs at half speed

Jeremy:

What does the contactor look like, and where is the push button you're referring to?

I'm wondering if my outside compressor/condenser unit has similar problem where the fan runs at half speed even when the indoor thermostat is switched OFF. - On 2011-07-09 by TN-Goose -

Reply by (mod) -

I agree that a bad contactor relay could also prevent a compressor from running, but I suspect that burning A/C controls, switches, contactors, or circuit breakers will often be traced to a compressor that is seizing and drawing high amps.

Condenser won't run unless I push the contactor

My outside unit will not come on in heat or ac I had the capacitor changed the defrost board changed I can push in the contacts and it comes on I have 24 ac to my tstat my fan in the attic comes on the heatstrips come on but no 24 volts to the contact to turn it on. My fuses are good the 3 amp fuse is good and I have 24 ac out of my transformer.

My wires are in good no breaks. I have a 3 year old goodman any answers deanclip@gmail.com.On 2018-11-14 by Dean

by (mod) - if jumping the thermostat connectors right at the control board doesn't turn on the A/C

Dean if jumping the thermostat connectors right at the control board doesn't turn on the A/C nor heat pump and when you know that there is power to the unit and it will start and run normally if you force the relay control switch closed, then I suspect

- a bad control board relay

- a bad control board

How do I install a MultiAqua chilled water fan coil system? Need piping diagram

I work overseas at one of our many U.S. Embassies. I have been tasked to install a

MultiAqua chilled water cassette 2- pipe fan coil unit and I can't seem to find a piping diagram for supply and return lines, with all the valves and controls in the proper sequence, anywhere. Not even the manufacturer could supply this info.

Can you please help? I want to make sure that this unit operates proficiently.

Thank you Desperate for info On 2019-01-21 by Thomas

by (mod) -

If the manufacturer doesn't have piping diagrams that you requested, I infer that it's because the specifics of how pipes are routed to and from the chiller depend on the physical properties of the installation site and perhaps have nothing to do with the operation of the unit itself, a long as the flow rates meet the design specifications.

I'd expect that the installation and operation manual for the unit would at least give the basic requirements for water flow rates or capacities.

Those two statements lead me to wonder if perhaps the root trouble here is just how you are phrasing your question or request. Perhaps if you go to the manufacturer with specific questions they can be of more help. After all they have a great interest in the successful installation of their product.

Do you have an IO manual for the equipment? If so I'd like to see a copy.

Reader follow-up:

Thank you for getting back with me. This is what I received from the manufacturer ( see attachment). I am a plumber by trade but I've never piped one in before and I'm the only one at the embassy capable of doing it.

I know it should have a bypass installed before the shut offs on both supply and return lines... but what comes after that?

I hope I made my question at least a little clearer. I know there are controls, strainer/drain port, filter, and I'm sure I'm missing something....and in what order do they go?
Thank you for your help

See MULTIAQUA A/C, Chillers, Fan Coil Units at

The company gave this advice:

It was a pleasure speaking with you. Attached is the IOM for the MHCFC4W for your review.

Unfortunately, we do not have or provide piping diagrams for this unit.

When installing control valves, I would suggest installing them in the supply line, so when the unit satisfies, water flow through the coil will be stopped.

Please ensure that the control valves are 24V, drive open/spring closed.