A/C compressor not working

DANIEL NISH

MEMBER
2015 HYUNDAI TUCSON
4 CYL
2WD
AUTOMATIC
146,000 MILES

Hello,

The A/C stopped working a while back. It would work for like the first 5 minutes then quit. After a while it quit working all together. We had the engine replaced not too long ago due to one of the connecting rods coming apart. We had asked the dealer if they could also find out the issue with the A/C since it wasn't working then. They said they would. When they called me to let me know it was ready, I asked them what was wrong with the A/C. They said they couldn't find anything wrong and only recommended replacing the discharge line as it had been seeping. Told them we would get around to it. Picked up the car, A/C was working fine for 2 weeks then it stopped again. We replaced the discharge line a had the system flushed. System was charged to 1.21lbs, still not working. We had already replaced the thermistor (evaporator temperature sensor) and high side pressure switch just because they were cheap. Still cannot figure out what is going on with it. Any suggestions?

7 Replies

KASEKENNY

MECHANIC
18,907 POSTS

If the system was charged then we can assume it is not low on freon but we still need to check pressures.

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

Does the compressor actually engage or does it come on and off quickly?

https://www.2carpros.com/articles/car-air-conditioner-not-working-or-is-weak

Let me know if you can get the pressures so that we can try and determine next steps. Below is a chart that shows possible issues based on the pressure. Thanks

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Tuesday, May 18th, 2021 AT 7:46 PM

DANIEL NISH

MEMBER
4 POSTS

Those are the pressures with the compressor off because it does not engage at all. We have a scanner thats bi-directional so when I try to command the compressor on through the scanner, it will not engage. I pulled the plug at the compressor and it has power. This would have been the second compressor to do this. The first original compressor would turn on for 5-10 minutes then shut down. Always on the first turn of the key after its been sitting.

When the old compressor was removed, it didn't show signs of coming apart or any internal damage. No dark traces or traces of metal. Albeit the second compressor was used, it did run for a bit then it did the exact same thing, run for 5-10 minutes then shut off.

When we had the engine replaced at the dealer, they said there didn't seem to be no issue. It ran fine for 2 weeks after the engine replacement then stopped again. It did lose.6lbs of Freon so we replaced the hose they recommended due to seeping. After that is when I couldn't figure out what is causing it to not engage. I thought maybe there was a code set and it wouldn't turn back in until it was cleared or whatever the dealer did but the scanner at work doesn't read an HVAC module.

I did notice there are 2 different dlc's on the vehicle. One in the usual spot below drivers knee bolster and one at the underhood fuse block. Don't know what the underhood one does.

Is there a way to manually bypass everything and engage the compressor? Like a jumper straight to the battery maybe?

Also, fuses and relay is okay. Any idea on what the electrical control valve does? Is it just a control to turn the compressor on and off according to pressure? Is there a way to test that?

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Tuesday, May 18th, 2021 AT 9:03 PM

KASEKENNY

MECHANIC
18,907 POSTS

Okay. That helps.

Just want to clarify one thing. When you checked for power was this when you were commanding the compressor on with the scan tool?

If you have power at the compressor then the compressor should be on.

When you are commanding the compressor on with the scan tool you are taking place of the engine control module so we can assume most of the relays are okay but we need to check them as well.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

The way this works is the power is feed to the top of the relay through the wire from the sensor 4 fuse and then the sensor 3 fuse. Then when the PCM wants the compressor on it grounds the relay on the AC relay control wire.

So we need to test this wire by putting your red meter lead on the battery positive and then the black lead on this terminal of the relay. Then turn the engine and AC on and if the meter reads 12 volts then the PCM is grounding the relay like it should. If not then the PCM is the issue.

Please let us know if you have questions on this. Thanks

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