AC Pressure question.

[elwesso]

Symptoms... AC starts out to be pretty cold then sorta fades off. Evap may be freezing..

Test procedure- Set AC at max cold, max fan, recirc, drivers window open, idled for 10+ mins at 1500 RPM (all specified by FSM)

After this time setting, pressures as read by my manifold gauge.

Low- usually around 30psi sometimes jumping up to like 33, no more than 35, then settles back to to 30 for a bit, then will jump.

High- pretty steady at about 175PSI

Outside temperature, roughly 75F with low humidity

FSM SPEC:L- 27.6-31.0H- 178-208.

Now at 175PSI im bordering on spec, and the low side is bordering on too high. Of course we are accustomed to that being a compressor related issue. However, with it being so close is it possible that there might be something else I could do to at least make the issue not so bad...

I just dont think its as cold as it should be.

Any comments appreciated. I will probably test this again as I think I may need a new seal for my gauge.

[Q451990]

Any chance you just need to add a little refrigerant?

Heath

[elwesso]

I would think though that would raise my pressures on both sides, yes?

[Q451990]

Possibly... not sure though.

What is the output temperature doing? You said it starts out cold, then tapers off. If you see it dropping to near freezing, and then warming up it's a sure sign the evaporator is freezing - which is also a classic "low refrigerant" warning sign. Typically when you see "smoke" coming from your vents on humid days (actually frozen water vapor) it's a sign of low refrigerant.

Heath

[elwesso]

I guess I can pick up a can of 134 and see what it does. Worst case I vent some into the atmosphere and call Al Gore!

[qship96]

I guess I can pick up a can of 134 and see what it does. Worst case I vent some into the atmosphere and call Al Gore!

why not get the system professionally evac/recharged for $100 so you know the freon level is perfect,and then if problem persists you have ruled out refrig. level completely?,and can begin looking elsewhere

[elwesso]

I had that done last summer and no change, why am not inclined it has to do with refrigerant level.

[qship96]

last summer was a year ago! if you are experiencing problems first place to check is proper refrig. level doing evac/recharge-maybe you have a slow leak? what are vent temps over time as it becomes less cool?

[elwesso]

i cant imagine that one year would do that much, plus its acting the same way it used to..

All I want to know is will low refrigerant cause low to be high and high to be low? I would think that both would be too low, but maybe as compressor discharge increases it will lower the low side more due to more "compressing" going on.

I dont see the need to do a full evac and recharge if I have gauges and I can see the pressures. I should be able to vent a little or add a little to tweak the pressure.

[qship96]

Look in the FSM,it has a diagnostic track to follow for every low/high pressure condition you could ever encounter! dont rule out improper charge,an o ring can spring a leak at any time-especially over the last year since you had the freon level EXACT from a proper evec/recharge

[Black stallion]

Then you lose out on all that experience you can only gain from doing it!

Wes, adding a bit of freon in small incriments will only affect your pressure in small amounts. Put a thermometer inside your middle vents as you add freon. This will let you know how the system is equalizing to the amount you add fairly quickly. Mine gets down to about 35- 4o deg on a 90+ day with 80% humidity.

If you notice the temperature/pressure fluctuate, then it could be the typical weak compressor scenario or I have had experience with a bad dryer coming apart and the "beads" traveled through the system and were trapped in the expansion valve. The freon would trickle through every so often and present the same symtoms as you described.

I would of course start with all the external components and if all else fails pull the exp. valve (call Al first). If its an older system that hasn't been opened for a while, it'll need a new dryer anyway.

[elwesso]

I did the test one other time (except the fan may have been on 2 fan blades instead of 4) and I got 175 / 18 @86F. Not sure that would have thrown my results off enough (the fan), but that sure does look like both sides are low. If anything, I would think that would have made the low pressure side higher. I think I may have a crushed seal in my gauge so I will check that.

I think im gonna add some refrig and see where we get.

[Black stallion]

True about the O-ring. Also it can hold under vacuum, but leak under pressure

[qship96]

[QUOTE=Black stallion]Then you lose out on all that experience you can only gain from doing it!

Wes, adding a bit of freon in small incriments will only affect your pressure in small amounts. Put a thermometer inside your middle vents as you add freon. This will let you know how the system is equalizing to the amount you add fairly quickly. Mine gets down to about 35- 4o deg on a 90+ day with 80% humidity.

35-40 degrees? with the fan on what speed? impossible with fan on high speed

[qsiguy]

In my experience the high pressure side goes up faster than the low side when adding freon. So if your high side is low but the low side is borderline ok, I'd add some. If the compressor is working properly the high side should climb faster. This has been the case on more than one vehicle I was servicing. My '94 Q and a '99 Ford Windstar, and a '98 Dodge P/U recently.

At 175 the high side is really low. Should be around 225-300 this time of year depending on the ambient temp. When I did mine ambient was over 100 and my high side was around 300 PSI.

[Jesda]

One year will make a difference if your AC is leaking. My old Q (now Evan's) would leak out about a can every winter. Same behavior.

[elwesso]

I think i may go to autozone and do this while in nashville, I didnt do it today so we'll see.

[elwesso]

In my experience the high pressure side goes up faster than the low side when adding freon. So if your high side is low but the low side is borderline ok, I'd add some. If the compressor is working properly the high side should climb faster. This has been the case on more than one vehicle I was servicing. My '94 Q and a '99 Ford Windstar, and a '98 Dodge P/U recently.

At 175 the high side is really low. Should be around 225-300 this time of year depending on the ambient temp. When I did mine ambient was over 100 and my high side was around 300 PSI.

What kind of speed would you add it. Would you just turn the valve on and let it creep up or would you open it in spurts?

[qsiguy]

When you first crack it open it spikes a little but it won't just rush in. Since you already have decent pressure I bet it would take at least 10-15 minutes to empty a full can. I use a manifold set, not the simple hose that connects to the can, so I can watch both sides at the same time.

Short answer, I just open it up and let it go. You can feel the can and tell how much is left in it. The part of the can that still has freon in it will be very cold. Don't turn the can upside down, you only want the freon gas, not liquid.

If you open it up in spurts I think it would be more difficult to get an accurate reading.

[elwesso]

Ok thanks. I will just let it do its thing and watch the pressures. I will also be charging with a manifold set. Would you say itd be safe for me to just wait until it gets to the correct high side pressure and then stop? Or woudl you stop shy of where you want it to be...?

[Jesda]

Dip the R134 can in a bowl of hot water for fast emptying.

[qsiguy]

I normally just watch the pressures and monitor the center vent temp. When it's plenty cold and pressure is about where you want it I stop. I've only overfilled once and that was when I replaced the compressor in my Q. I overfilled because the system wasn't up to operating temp while I was filling it. If the temp of the engine and the ambient temp isn't as hot as it'll be on a normal days drive I would stop earlier to make sure you don't do too much.

[Q451990]

Dip the R134 can in a bowl of hot water for fast emptying.

I do this too... makes a huge difference!

Heath

[Black stallion]

Right you are. Low speed. High is about 45 - 50

Also failed to mention my incriments were from a 30lb canister and not the small cans