cornsnake19

So I've noticed that my 2000 Honda Civic EX has a weird ac problem. When starting the car up in neutral the ac blows cold air with no problem at all. But after starting out in first it'll warm up and it no longer blows cold air. As I shift through the gears I notice it only starts getting colder once I shift it into 3rd gear, where it stays the same temperature all the way up into 5th gear. The car is old, and I'm pretty sure the AC hasn't been serviced in a while, but could it be a compressor problem, a refrigerant problem, or just the fact that the AC hates low gears. Any help is appreciated because these Kansas summers can be brutal.

fragmare

When in 1st/2nd, do you hear the compressor clutch disengage while driving? If so, what are your RPMs when it disengages. Do you own or have access to a set of manifold gauges?

cornsnake19

No, I hear the compressor clutch going at all times, and there's no RPM increase or decrease. And I don't own a set of manifold gauges. I doubt it's also a charge in the coolant lines as well, as it of course blows cold air.

fragmare

If the compressor clutch is engaging and staying engaged when it's supposed to, that means the hi/low pressure cutoff and thermal protector cutoff are both functioning properly, at least. That doesn't rule out a slow leak reducing your high/low pressures just enough to notice in certain gears, but not enough to cause the compressor to "short-cycle"... in which case a set of manifold gauges and a dye charge would come in handy. Even if your A/C blows cold at idle, a set of manifold gauges can tell if you're pressures are a bit low, which would indicate a minor leak. If the A/C has never been serviced, there's probably no dye in the system. They typically use the clear/amber PAG at the factory, iirc. If that is the case, I'd chuck a 1/2 oz or so of green A/C dye in the system and run it for a few days, then look around for leaks (preferably with a black light). Aside from that, it's really hard to properly diagnose A/C issues without manifold gauges. It's basically a guessing game, at that point.

mk378

You need to check if the compressor is engaged when it is not cooling. That means pull over open the hood and look if the front plate is spinning. Two big reasons for intermittent cooling are the compressor clutch being too wide, so it doesn't always pull in, or the expansion valve is sticky. Seeing if the compressor is engaged or not is the first step in differentiating the problem.

Lack of refrigerant will not cause intermittent cooling. If it gets cold once, there is enough refrigerant. Also as the Civic has a TXV system it will not "short cycle" if it were undercharged.

If the compressor is engaged, feel the large line from the firewall to the compressor. It should be cold. Don't touch the smaller high side line it will be very hot.

fragmare

If he pulls over and and opens the hood, he'll no longer be in 1st/2nd gear, so i doubt he'll be able to "catch" it that way. He stated he hears the clutch engaged at all times. Clutch plate to pulley clearance could be out of spec, and is always worth checking with a set of feeler gauges. If anything is stuck open (expansion valve) or restricted (condenser) within the system, it's sure to have an effect on the operating pressures of the system. Speaking of the condenser, visually inspecting the condenser fins are not clogged up with dead bugs and road grime is always worth doing, as well... If it were me, and the clutch clearance and condenser fins checked out, I'd still try to get hold of some manifold gauges and check the pressures are within spec.