Any dash A/C guru's here?..a few questions....

[Motor7]

I bought a HF set of manifold pressure gauges. Hooked them up and this is what I am getting with the engine @ 2000 rpm:

Low pressure at 10, high at 175...then they both drop for about a min or so to low-45 & high 125....then the compressor "clicks in" and it goes back to 10/175.
Temp reading at the vent on fan speed 3 and re-circulate is 51 degrees(temp outside today was 65F.)

This is my first attempt at testing/diagnosing a dash a/c....I'm thinking it needs Freon since it is short cycling. However, the yellow hose on my gauge set has no pricker for the can of R134A, so when I screwed the can on to the hose it could not pierce the metal seal. I reckon I am missing something eh?

[Motor7]

I just read more of the the reviews on the gauge set-

AC Gauges - Save on this AC Manifold Gauge Set

Apparently it does not come with a 134A can tap so I ordered one from Amazon for $6 shipped. I know this is a cheap gauge set.....but no can tap...really? ...argggghhhhh

[ga traveler]

When the compressor is off, there is enough pressure on the freon pressure switch to close the switch and turn on the compressor. As soon as the compressor cuts in the pressure drops on the low side and the switch cuts out. You need to add freon. DO NOT OVERFILL.

[Old Scout]

Lots of good info on the internet about recharging auto A/C units. Basic rule of thumb is about 20-25 degree dif between air from vent vs ambient air.... These are charts for all this but at 65 degrees ambient, low side should be in the 25-30 range and high side in the 150-175 range--estimate. Need to make sure both the evaporator and the condensor rads are clean and getting good airflow--bad air flow means bad diagnosis results. With the low side at 10 and the high side at 175--might be bad air flow or a partial freon block at the expansion valve or the filter/accumulator.

[kkeever]

When the compressor cycles off the two pressures should equalize. since it is not even close I would suggest the there is a blockage somewhere in the system. if there is, the refrigerant will need to be recovered and then a vacuum pump connected and a vacuum pulled down to a minimum of 500 microns and held for at least an hour, then recharge with the sticker plate amount of refrigerant.

[Motor7]

I appreciate all the info...and I have been watching "youtube's" about this and I agree...possible blockage. So what causes a blockage?

Also, since it is cycling pretty quickly, like ga traveler says...possible low freon. Since I don't know how much is in there I am concerned about overfilling, so it looks like I will either buy a vacuum or take it to my local mechanic and have him vacuum the system.

kkleever...500 microns? Hmmm, the biggest pump HF has is a 3CFM that pulls down to 22.5 microns for $150....don't wast my money?

[kkeever]

It would be less expensive if you found a reliable auto mechanic that is certified working on automotive AC systems. the vacuum pump does not measure microns and so you would need to purchase this also. Then you would also need to have a compound gauge set, then a reclaim machine, then a cylinder to hold the reclaimed refrigerant, then the knowledge and expertise for using them effectively.

The blockage is most likely water vapor that during operation freezes at the expansion device, thereby blocking it. upon shut down the vapor thaws and you start again.

A refrigerant leak is what probably what got this all started.

[Motor7]

kk, thanks and that makes a lot of sense. You are right about the leak & it looks like the shrader type valves on both the high & low side are both bubbling after I added in a can of freon. The added freon made no change in the erratic pressure, so I will take it into my mech asap.

[wa8yxm]

That low side pressure is way way way too low.

And it's called Coolant,, Freon (R-12) is not used any more.

[kkeever]

Freon is a trademark of DuPont and is used for all refrigerants not just R12. I his case probably R134a.

[dieselclacker]

Refrigerant in air conditioning, coolant in engine.

[Motor7]

Yep...dinosaur here...always gonna be FREON!

[DD788Snipe]

Don't worry too much about the high side pressure. Low side should be around 25lbs to 50lbs depending on ambient air temp. The hotter it is the higher the pressure. Also a good way to make sure the system is charged is to check the cooled air temp when adding coolant. Get a pocket thermometer and put it in the closest dash vent to the evaporator. Your output at the dash vent should be close to 40 degrees when fully charged. Charge with the setting on Max so as not to suck in hot engine compartment air. A laser thermometer will also work in a pinch. Take precautions. You are working with gases under pressure. Becareful not to over charge the system.

[kkeever]

R134a has a lower suction pressure than R22. Most marine ACs are water cooled and should never see 50PSI on the suction. and the high side is still an important piece of the puzzle when trying to troubleshoot a system that is not operating correctly.