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The AC failed suddenly out of the blue, took it to the shop. They replaced the compressor and stated there are no leaks (after testing with dye). However, the AC now takes, on a hot day, 15 minutes to start to make the interior of the car somewhat comfortable. I took it back twice. The first time they recharged and sent me home again. The second time they said that by process of elimination, it is clear that the condenser also needs replacing. (At first they said there is no test to see if the condenser needs replacing; when I probed further, they said they could check the pressure at the input side and the output side, but there's really no need, because there are only three potential problems with the AC, the compressor, the condenser, and leaks.)

The weather report says we're in for a cool, rainy week coming up. Should I wait until the following week to take it for the condenser replacement, so as to be able to judge fairly whether the condenser replacement truly results in properly working AC?

In case you want to know about the car: 2004 Corolla. AC worked fine up until that sudden failure.

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  • A fourth problem is the evaporator...
    – Solar Mike
    Jun 3, 2018 at 6:06
  • In the meanwhile, you can try a little something yourself. Replace the cabin filter and thoroughly wash the condenser if it's dirty. Try straightening any bent fin. Check for any dirt between the condenser and radiator and try to remove it. Replace any sealing material between the condenser and radiator (any high density foam material and high temp glue suffices).
    – Al_
    Jun 3, 2018 at 7:08
  • Do you know how it failed? Did it seize and contaminate the system (anything from the compressor to the dryer) with metal powder? In that case, parallel flow condensers must be replaced, since they can't be flushed. They also ought to have replaced the TXV and receiver dryer in that case. In the case it didn't contaminate the system, they could have put too much oil in your system and this is hampering cooling capacity by pooling inside the condenser. With TXV systems, the evaporator is rarely if ever affected by contamination, but a dirty cabin filter can seriously hamper the cooling capacity
    – Al_
    Jun 3, 2018 at 7:14
  • Related question: mechanics.stackexchange.com/q/55038/38092
    – aparente001
    Jun 11, 2018 at 15:01

2 Answers 2

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It could be the climate control unit that is not operating correctly. They often have servo controlled flaps that control the flow of air over the heater and evaporator to adjust the cabin air temperature.

First thing to check is that the compressor is running. You should be able to identify the AC compressor in the engine compartment. It will likely have a clutch on the front of it that engages when cooling is turned on. Watch the pulleys turning (keep fingers away), then get someone to turn the AC on full. You will likely hear a click as the clutch pulls in. The front of the compressor clutch will then start spinning. It should keep turning and should not keep turning on and off.

Then check the refrigerant pipes that pass through the firewall into the cabin. You should find that one gets very cold and may even start to frost up. If it is getting cold I would then start suspecting the climate control unit in the cabin.

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You can't just change a compressor and recharge. You need to at least change dryer and flush the system and in some cases you may need to change the expansion valve. See here for detailed information about compressor and replacement of it.

There are ways to check if parts of AC system is working properly. As you mentioned, this involves checking pressures and temperatures at high and low pressure sides. This may be too technical for your mechanic. When I got my AC repaired and it was making vibrations at very hot days, the just did vacuum/refill(recharge) again because they didn't know what was the problem since car computer didn't log any errors. facepalm :) See this: http://rechargeac.com/how-to/ac-system-pressure-chart

I think you should get your mechanics suggested repairs done right away and start testing. I am guessing they will give you more than 1 week warranty on work anyway, so why not get it done right away?

The problem I see here is that obviously they don't know the reason and they will keep changing parts until issue is resolved. So you shouldn't pay for the work unless the issue is resolved. The problem can be expansion valve, evaporator, incorrect refrigerant amount, condenser, clogged dryer or even a faulty compressor. I would definitely force them to check for pressures/temperatures or promise warranty on fix or free. Knowing what was originally wrong with your compressor may help.

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  • You're wrong about the flush. Flushing is only mandatory if a great deal of oil was lost or if the compressor spewed its bowels across the system. Flushing can be a very demanding job and it's avoided if possible, because 1)nearly anything except compressor has to be flushed 2)every flushable part (parallel flow condensers CANNOT be flushed for example) needs to be flushed one at a time and 3)the TXV/OT has to come off because the evaporator can't be flushed through a restriction (and not every car gives you the courtesy of letting you remove the TXV from the firewall and not from the dash).
    – Al_
    Jun 3, 2018 at 18:13
  • About the vibration, it can be normal. Any ac compressor pumps the refrigerant in pulses and that means vibrating lines. Higher ambient means higher discharge pressure and stronger vibration even if some compressors adjust their pumping capacity according to evaporator temperature/cooling demand. Some systems, especially bus or high end cars ones, often feature discharge mufflers to reduce vibration. One way of ruling out abnormal pressure is reinstating the specified charge.
    – Al_
    Jun 3, 2018 at 18:22
  • However, there are other conditions which can cause higher than normal discharge pressure, such as improper condenser airflow (for example, too many bent fins, too much dirt, hot engine bay air being pulled by the fan instead of ambient one). Failing all of this, it can either be a vehicle design (such as noise proofing) issue or a line vibration dampening one. Unfortunately, diagnosing AC systems can be a very hard task.
    – Al_
    Jun 3, 2018 at 18:23
  • Go to: hella.com/techworld/uk/Technical/Car-air-conditioning/… Check number 5, instructions. You should always flush the system. In either case, the will be metal particles in system even if there was adequate oil and compressor did not blow. Same as your engine oil, moving parts create tiny metal debris. If you check the hella pages, it says the that when a compressor fails, you should assume that there is contamination.
    – Evren Yurtesen
    Jun 3, 2018 at 19:56
  • It says that system contamination must be always assumed when there's a compressor defect, but a compressor defect can also be an open clutch coil and this can happen on a perfectly healthy compressor. The compressor is usually replaced when seized, but many shops seem to like solving problems such as open coils and defective control valves (or even simpler issues) with a compressor replacement. In TXV systems any dirt is caught by the condenser coils and receiver dryer (also unflushable parts-must be replaced) anyways, so, again, flush is done only when strictly needed.
    – Al_
    Jun 3, 2018 at 20:50

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