High 'Low-Side' Pressure

[Howie T]

Hi, newbie here looking for a bit of enlightenment. My son's 2013 Ford Fiesta's aircon isn't working so I thought it might just need a gas top-up. After doing a bit of on-line research I bought the STP EZChill aircon kit at a local car accessory shop. In accordance with the instructions I connected the gauge up to the Low Side charging port expecting to see a reading of zero or close to it, confirming that a re-gas was needed. Instead I was shocked to see a reading of about 100psi, at which point I was out of ideas other than a realisation that this is obviously a job for the pros.

That's now my next move but, in order to give me a bit more of an understanding of how this stuff works as well as an ability to develop a BS meter for use when talking to the people who will be doing the job, what's likely to have gone wrong with the system to cause such a danger-zone reading?

[Cusser]

Good that you did not "use a kit", some can damage a system permanently.

Ask your friends/look online for an independent ASE repair shop (ASE certified) that they like.

For you, start up the engine with AC off, and look at the AC compressor; you should see the outer pulley turning but the center section not turning. Now turn on the AC switch and blower, talke another look; this time the center of the AC compressor should also be turning.

Question: do you fell ALL your blower fan speeds out the vents? And strong air flow?

[Howie T]

Thanks for your helpful response Cusser. The car's back with my son at the moment so I don't have immediate access to it but I'll certainly try the AC off/on treatment and check the clutch/compressor action as you suggest. The fans respond well enough to the dashboard control (significant increase in fan noise with each increase) but not much air seems to be blowing through the vents, certainly not as much as I would expect.

[Howie T]

I replaced the filter about a month ago as part of the service routine. What might cause the pressure to be so high?

[Cusser]

The fans respond well enough to the dashboard control (significant increase in fan noise with each increase) but not much air seems to be blowing through the vents, certainly not as much as I would expect.

Well, with small air flow out the vents, either the air flow is being diverted to the windshield (like defroster path) or under the dash (heater path), or there's an obstruction in the air path like leaves, leaky evaporator causing gunk over its coils...

...or fan could be spinning at all speeds but the squirrel cage fan blade is loose on the blower motor shaft and not turning !!!

[Howie T]

Well, that's certainly given me one or two things to consider!

[Dougflas]

And being it is a Ford product, you could have a problem with a blend door.

[Howie T]

Just looked up 'blend door' and I do see what you mean; the lack of puff might well be down to a faulty actuator. However, even if that's the case would it also account for the dangerously high pressure in the system?

[JohnHere]

Did you check the low-side pressure with the AC compressor running or with it off? If off, a (static) pressure of around 100 PSI is fairly normal depending on temperature and whether the system is fully charged. Bear in mind that you can't gauge how much refrigerant is in a system by pressure alone.

[Howie T]

I checked it with everything switched off prior to my intention of checking again with the engine running and AC on. However, with a reading of 100psi I chickened out of going any further. The several Youtube videos I watched prior to giving it a go all showed either a nearly-zero or very low reading, both system on and system off, prior to connecting up the re-charge bottle and gradually building up the low-side pressure to the recommended readings. On the instructions included with the kit it does say that pressure readings in the red could indicate a mechanical malfunction and not to proceed.