The A/C compressor went out on my '05 Sienna.

I replaced the compressor but not the receiver/dryer and expansion valve.

Now the A/C is sort of working right: It has separate front/back controls. If both front and back is on, it works fine. Blows nice and cold. However, if just front is on, it does not get cold and blows barely below cabin temp air.

My question is: Is this a situation where not fixing it could cause further issues, or is it fine to leave it like this and deal with the minor inconvenience of having to have both the front and back on?

  • What happens when just the back is on? Also when just the front is on and the air is not cold, how is the pressure coming out of the vents? Does it still blow as hard as it should, just not at the right temperature?
    – Jason C
    Commented Sep 21, 2016 at 15:48
  • 1
    Haven't tried it with just the back on. As for pressure, I do not notice any difference in how hard the air blows, only the temperature. I will specifically check both as soon as I can and edit that into the question
    – Kevin
    Commented Sep 21, 2016 at 16:04
  • "Doctor, it hurts when I do this! - Well, don't do it, then!". If the A/C doesn't work properly when only the front is on, not running it with only the front on won't cause any "issues", except the obvious one that you don't have any A/C. If you really want it to work with only the front on, then take it to somebody competent to fix it.
    – alephzero
    Commented Sep 21, 2016 at 21:46

3 Answers 3


My experience with AC is limited to what I have been studying both in book and video form. From everything I'm reading you really do need to replace the receiver drier when you replace the compressor. This is due to the excess moisture allowed into the system as it's open for the repair. Also, if the compressor was damaged causing the need to replace it, bits of the compressor may have collected in the receiver drier, and now will flow back to the compressor.

Was a vacuum pulled on the system before recharging it? If not, then excess moisture is still in the system and could be damaging the AC system components. Pulling a vacuum on the system boils off the moisture inside it without needing added heat. If this isn't done, there will be moisture left in the system, and that's bad for your AC.

  • Yes, he did pull a vacuum.
    – Kevin
    Commented Sep 21, 2016 at 15:40
  • That's good. So it's less likely to be causing damage from moisture, but I would be concerned about debris that might be in the system from he compressor failing. Much of which can collect in the receiver drier.
    – cdunn
    Commented Sep 21, 2016 at 15:44

Sounds like an electrical wiring sequence problem.

As such, being in a minor system like A/C, there's probably no damage being done to the system by having it wired as it is. The ideal, of course, would be to take out the systems and re-wire them as they should be wired. However, you're not risking blowing something up or anything by leaving it as it is.


Just take it to a professional shop. Aircon work is covered by a lot of legalities (such as never opening the system to the atmosphere) which most shadetree mechanics don't even know about.

You tried to get the work done on the cheap, and failed. You should get it fixed properly now. Ask for a detailed quote first, because we (and you) don't know the current state of the system in your car.

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