Air Conditioning - Help with Carrier 50YQ

Can anyone please provide a circuit/wiring diagram for Carrier heat pump model number 50YQ048310. The original diagram that was posted in the unit has disintegrated and Carrier has been unable to help me.

Can anyone offer any tips for diagnosing the following problem:

Heat pump cools well, with over 25 deg differential with outside temperature 100F. With thermostat set to a low temperature the unit will run for over 1.5 hours maintaining same differential between vent and return. Sometimes the unit does not cool when the thermostat demands it. The inside and outside fans are running so I'm assuming it may be a problem with the compressor start components. If the unit is turned off for 10 minutes it works ok next time.

I have maintained this unit for over 20 years. Work done has included changing the main contactor, replacing the outside blower motor, and a couple of R22 top offs. Recent work included bypassing the outside coil temperature sensor that was open circuit preventing the outside blower running. Also added R22 as pressures were low.

thanks for any help

Andy

Replace the compressor run capacitor. Step away from the sealed system.

Thanks for the reply. I asume then that it's normal to expect the compressor to start most of the time if only the run capacitor is good, is that right?

If so then I assume the problem could be the start capacitor or the start (potential?) relay. I'll see if I can find which tomorrow morning when it's cooler.

Wish I had the schematic!

thanks again

Andy

Just started "My free web page" from provider.

If you go here:

http://jarredsdad.embarqspace.com/#/welcome/4529420987

You should see a link to the right of the coffee cup that says 50yq-3w in Red. That's your diagram. You'll have to find your unit as this covers many.

If it doesn't work send me a PM with an email address.

This is the first time I tried this webspace stuff.

Hey, you fix my web "page", I'll fix your A/C.

I tried it and it worked.

Have to get all that other junk off of there. Some manuals are up to 10Mb, wonder if I have space.

Anyway your unit is on page 6 of the pdf.

Thanks a lot. I was able to download the document and find the data for my unit. Really appreciate you taking the time to post this.

Andy

Sorry Saturn for some reason I misread your reply and was thinking you said change the start capacitor. Can you, or someone else, give me a bit of education on how run and start capacitor failures affect the system.

I understand from looking at the schematic that both the run and start capacitors are in parallel during start and then the start relay opens the start capacitor and then the start capacitor is bled down by its resistor.

I asume then that either a bad start capacitor or a bad run capacitor could cause the compressor not to start but can it run if the run capacitor is bad.

I visually inspected the unit this morning and neither the start or run capacitors show any sign of leakage or distortion.
I tried testing the start capacitor for leakage but then realized the test was not valid unless I removed the resitor from the terminals.

Can someone tell me the Carrier part number for the start capacitor or can I just replace it with any capacitor with same capacitance and voltage rating as long as I add the resistor to the terminals. Same for the run capacitor, carrier part number or just go with same ratings?

thanks for the help!

Andy

The start cap basically gives the motor a kick in the butt to get it moving. Once up to speed the common winding will energize the potential relay and take the start cap out of the cicuit and leave the run cap in.

The run cap basically advances the electrical sine wave. This lets the motor run more efficient and cooler.

It could run in some cases with a bad run cap but wouldn't start with a bad start cap.

Never change the start cap without changing the relay also.

You don't have to use carrier parts. Same spec parts are available at the supply store.

Part Number P283-9915

DESCRIPTION RELAY-START
CONTACT RATING 50 AMP PICKUP VOLTS 195 -224 DROPOUT VOLTS 60 -123
MAX OPER VOLTS 420

Part Number P291-4054

DESCRIPTION CAPACITOR DUAL
MFD COMP 40 MFD FAN 5 MAX CAN HEIGHT (IN) 5.9

Carrier site had no specs for the start cap other than part number.

What is important for you are the specs for the start relay, get an exact or very close match.

Thanks for the info!

This morning I was on the roof and saw/heard the outside fan shutdown leaving the compressor running. I'm now suspecting that my problem may not be the compressor start components but that, when the outside fan shuts down, the compressor overheats and shuts down and will not start the next cycle until it cools off.

Next step I suppose is the find out why the outside fan motor is shutting off. I assume it's overheating. I replaced the motor about 6 years ago as the original one had severe bearing wear. I think I mentioned earlier that the start of all these problems was that the outside fan was not running and and I traced that to an open outside coil defrost stat. I bypassed it thinking it would not matter until the winter when the unit is in heat mode.

I know it's time to change this unit for a new more efficient one, but I need to keep it working a bit longer while I get quotes for replacing the system.

thanks again

Andy

Could very well be the cap for the fan.

I sat down by the pool with a beer yesterday evening and studied the schematic. Found out that the bypass I had done had the effect of allowing the unit to go into defrost mode when the defrost timer tripped even though the unit was in cooling mode. That of course shuts down the outside fan motor probably causing the compressor to overheat and shutdown. This morning I undid that error and completely isolated the outdoor fan from the defrost circuit. I'll monitor it for a day or two to see what problems are left. I know I'll have to restore the defrost circuit before winter but I may have a new unit installed by then.

The schematic made all the difference to understanding what's going on. Thanks again for posting it.

Andy

As Jay says "If you can do it we can help".

Just in case anyone is interested my A/C worked fine for the rest of the summer. The problem was caused by the external fan motor capacitor. It caused the fan motor to overheat and go into thermal shutdown. The compressor then overheated and shutdown. Just changing the external fan motor capacitor fixed it.

Thanks for the help.

Andy

Carrier heat pump model number 50YQ048310.

Well, as I reported earlier, the unit functioned perfectly in cooling mode thanks to the help provided here.

Now it's winter and I have a new problem. The outside coil was icing up badly on cold mornings even after I restored the wiring to enable the defrost circuit. There was a huge drop in vent temperature when the coil iced up and the icing did not clear unless I ran the heat pump in cooling mode.

I bypassed the defrost thermostat (DFT) and the unit now operates as expected - every 90 minutes of run time it goes into a 10 minute defrost cycle and the ice is cleared. With the defrost thermostat bypassed the unit will always run a 10 minute defrost cycle even if there is no icing so I need to replace the defrost thermostat which I assume is not closing when icing is present. ( I have avoided going up on a frost covered roof to measure the DFT with icing present )

Can someone please provide the part number of the DFT for this unit?

The DFT is attached to the lower line of the outside coil. Does the probe actually go into the refrigerant line and will changing it require recovery,evacuation, and recharge?

thanks for the help!

Andy