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I recently purchased a used 2006 Honda Civic Si. The AC system is not working as the system does not blow cold air. The clutch on the compressor is not engaging, however the condenser fan is running fine and all the lights for the AC inside the car come on. I got a can of the recharge refrigerant but the guage indicated not to recharge as something else was wrong (needle in the red). I replaced the compressor relay but still no luck. What is the next step in checking what's wrong?

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First of all check if the compressor is still good. Engine off and keys in pocket, reach the compressor with your hands and rotate the clutch hub (the front part on the compressor's clutch assembly). Check for uniform resistance across one whole turn. If it seems to "catch" or can't rotate completely, compressor's bad.

If the compressor's good, locate the clutch coil terminals and check for resistance at them. Should read between 3 and 6 Ohms. If not, either the clutch coil is bad or the thermal switch on the compressor's body (check if it has one, basically something with one cable going to the clutch coil and the other to the terminal) is bad and became permanently open. Also, check for voltage on the compressor clutch power connector coming from the harness when engine is on and AC is on. If the clutch coil terminals shows proper resistance and there's no voltage at the connector, you have to look elsewhere than the compressor (refrigerant charge and leaks, pressure switches, wiring etc).

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  • Should I disconnect the belt before trying to rotate the clutch?
    – user40054
    Jul 17, 2018 at 19:45
  • If the compressor has a clutch there's no need to. The clutch hub (google images for "ac compressor clutch hub" to see what i mean) is always mated to the compressor's shaft whether the clutch coil is powered or not. If it's clutchless then yes, you have to rotate the pulley and the belt has to come off.
    – Al_
    Jul 17, 2018 at 21:02
  • Okay, I tried rotating the compressor clutch and it seemed pretty even in the little resistance it had.
    – user40054
    Jul 17, 2018 at 22:52
  • It should be pretty firm/ hard to turn. If it spins way easy then you may have a broken compressor shaft.
    – zipzit
    Jul 18, 2018 at 0:32
  • Resistance depends on ambient temperature (greater ambient means greater static refrigerant pressure). If it had some resistance and this resistance was even, then the compressor internals are good. What zipzit means happens when the clutch hub looks to be just freewheeling.
    – Al_
    Jul 18, 2018 at 8:53
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With your gauge indicating in the red, this would indicate a potentially serious problem with your A/C system. With this, I would strongly advise taking this to a certified Motor Vehicle Air Conditioning specialist for diagnosis as additional specialty tools will be required to determine issue accurately. This condition is likely beyond what a home mechanic can solve on their own without the appropriate equipment and knowledge.

The main issue here is you do not have a proper gauge manifold set to determine what the high side is indicating, and we do not have a "reliable" low side reading. Without a proper high and low side measurements anyone would be guessing at what the problem is.

This could be a problem with the Thermal Expansion Valve (TXV) being jammed, or the system was overcharged by someone at some point, likely the previous owner.

IMPORTANT: Willfully "venting" (discharging to the atmosphere) refrigerant is a violation of federal law in the United States and in many other countries. Recovering refrigerant must be done by licensed and certified personnel only.

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  • I'm in the US. Typically will AC specialists charge a base fee just to find the problem with the AC system? Also, would a blown fuse cause the gauge to show red?
    – user40054
    Jul 17, 2018 at 19:44
  • Also, if @AI_ is right and it's the compressor, couldn't I just change it myself after getting the refrigerant evacuated at a shop?
    – user40054
    Jul 17, 2018 at 19:47
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    @OP if the compressor seized the system needs to be flushed (the condenser and receiver dryer will need replacement too, and the TXV will have to be replaced if dirty) and a proper flush requires specialized and expensive equipment, better if you have everything done. If you have a faulty coil you can replace it with a scrap compressor/replace the coil on the still good compressor yourself, provided you have the refrigerant legally recovered by a specialist first (and in that case you better replace that receiver dryer too)
    – Al_
    Jul 17, 2018 at 22:06
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    Remove the old receiver dryer, drain any oil left inside into a graduated container, measure the oil quantity and write it down, then have the new receiver dryer fitted by who you task with vacuuming the system and charging the refrigerant and tell him/her to inject the oil quantity (which you wrote down), type and viscosity (read type and viscosity on the compressor's label) you drained from the receiver dryer back into the system along with the refrigerant, in addition to the oil quantity reclaimed during refrigerant evacuation. Again better if you have it done because oil can be hygroscopic
    – Al_
    Jul 17, 2018 at 22:09
  • The main thing to be aware of here is that even if it is your compressor, you will still need to recover the refrigerant to replace it. 2 things to be aware of it's possible maybe your low pressure switch has failed. But you can't confirm this without getting a proper high side measurement. Because it's also possible it's been overcharged and the high pressure cutoff is currently engaged. Some folks have a TXV fail, and then they overcharge using these DIY kits because a bad TXV can pull a vacuum on the low side making it look like its low on refrigerant. Without gauges, you're gambling.
    – Jeep Cherokee Rescue Society
    Jul 18, 2018 at 18:43

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