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We have a 2002 Honda Odyssey that has a really weak A/C.

  • The refrigerant is full
  • It gets a bit cooler when put into park
  • It gets a bit cooler when the rear fan is turned on

I'm guessing it could be something electrical, but it can't be a relay, as it gets a bit cool...

Any ideas?

  • By coolant, do you mean engine coolant, or refrigerant in the AC system? What do you mean by "completely full"? – mongo Jun 19 '17 at 23:50
  • Sorry, did mean refrigerant. Completely full meaning it won't take any more refrigerant from a recharge can. – QwertyChouskie Jun 20 '17 at 3:36
  • Did you measure the coolant pressure? If so, what was it? – GdD Jun 20 '17 at 7:07
  • In an A/C system there is such a thing as over full. An overfull system would cause cooling problems just like a low system. The only way to know that a system is full is to have it evacuated by a machine, then recharged to the correct amount. That amount should be on a sticker under the hood. Only after that can the discussion continue. – vini_i Jun 20 '17 at 19:33
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The refrigerant is not supposed to be made "completely full" rather a charge is measured by weight. Failing that, the other accepted method is to charge, and observe the behavior of the low side and high side of the refrigeration system. That requires two gauges to do properly.

The system relies on the fact that condensed, liquid refrigerant needs to "boil" in the evaporator in the car, to take heat from the air. If there is too much coolant in the system, it cannot "boil", and it cannot condense to a liquid.

I am not confident with the OP observations. Normally a system "completely full" would stall the compressor or the compressor would not start.

So here are some questions:

  • When running the AC is the compressor turning (and do you hear the clutch engaging so that the belt pulley turns the shaft of the compressor)?
  • How long does the compressor run? Continuously, or for short times like 5 seconds or so?
  • What is the ambient temperature, and what is the temperature of the air coming out of the vent in the vehicle?
  • Is the engine cooling fan running when the AC is turned on for the car, and does it stay running when the compressor turns on and off?

Unfortunately, a complete answer is not possible given your information, and it is necessary to get some questions answered first. Alternatively, a complete answer would be a book (grin).

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Turns out it had lots of water in the coolant lines, which was making the system barely work, despite being properly pressurized and the pump running.

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