I'm burning up! Need AC help!

[drdave]

OK. Near mint 90 had wonderful AC up till yesterday. It was retrofitted in 98 and about three weeks ago I had it vacuumed and re-charged.

Yesterday morning I noticed that the compressor didn't come on when I first started the car, and then short cycled as I drove. As hot as it is, it should be on all the time.

So I take it back to Goodyear and have them vacuum it again and re-charge it. With an outside temperature of 94, the engine hot and at idle the low-pressure side is between 50 and 55 psig and the high side between 350 and 400 psig. The high side seems way high to me, but I really don't know what it should be.

The best temperature at the point of my vents now is 60. It was between 46 and 50. My compressor still wants to cycle now, so I bypassed the switch, since adjusting it had little to no effect.

I'm in Texas and I'm dieing here. All of my AC plumbing seems to be getting pretty cold and sweating. I'm not sure where to look now. Please help.

 

[rangerj]

DrDave,
The high pressure side should be approximately 240 psi to 300 psi. You're running on the higher than normal, or expected, pressure range in the high pressure side of the system. 50 psi on the low pressure side is within the expected range.

Did you replace the filter/dryer when the system was converted to R-134a?

High discharge (high side) pressure, and normal suction (low side) pressure suggests the following be investigated;

Situation: normal suction side pressure, High discharge pressure, and Clutch cycle time = continuous run ie not cycling.
Possible causes:
1) engine overheating or operating at higher than normal temperatures,
2) refrigerant overcharge, air in refrigerant, humidity and ambient temperatures very high,
3) a blockage between the high and low side. Was the system flushed when it was converted?

When your system was recharged recently did the mechanic put a full charge for an R-12 system, that is 36 ounces of refrigerant, or the correct amount for a conversion, that is about 85% of 36 ounces (approximately 30 ounces)of R-134a)?

Was any oil added? If the system leaked down, it will have also leaked some oil. A recharge because of a leak should include an ounce or two of oil to replenish the oil lost! The oil in the system circulates with the refrigerant, so that if refrigerant leaks out, so does some oil! This is a judgement call on the part of the mechanic. To much oil is as bad as to little.

Discharge pressures (high side) are expected to be 175 psi to 300 psi in the ambient temperature range from 60 degrees F to 100 degrees F.

Vacuum pressures (low side) should range from 45 psi to 60 psi in the same temperature range per the Ford shop manual (as well as other sources).

Hope this helps,( Per SDPATT, who lives in your kind of climate, the pressures 50 psi, and 240 psi, work real well. He gets 37 degrees F out of his center vent, This is ideal.) rangerj

 

[jthomas68]

I`m going thru some a/c work right now.I also am getting too much pressure(was 500 psi,now down to a still to high of 350+)From what i`ve been discovering,there are only two reasons to have such high psi on that side.Either too much R143A(should be 2lbs 14oz),or a blockage.You may want to change out the oriface tube(there is a kit for $14),or,in my case,the condensor is plugged.With the pressure as high as you1ve stated,i wouldn`t run the a/c unless you want to run the risk of blowing out an o ring.

 

[drdave]

The system was converted by Midas in 1998, long before I got the car. The stated charge on the conversion sticker was 2.1lb of 134a and 8 oz. of oil. This combo seemed to work well, as I've been getting in the mid 40's out of my vents.

I noticed that I had a slow leak in my high pressure Schrader valve about three weeks ago, so I took the car to Goodyear. They simply vacuumed the system, replaced the Schrader and recharged the system. I think the mechanic only put in about 24oz of 134a, but the system worked acceptably well.

What ever happened did so suddenly. What's strange is that it caused my low-pressure switch to think there was too little pressure in the system. Even with the current charge I had to adjust the **** out of the low-pressure switch just to get it to stop short-cycling.

I may screw with it a little longer and then may give Scott a call to see if he'd be interested in lending a hand. I'm fortunate in that I live about 30 minutes from him.

 

[sdpatt]

David,

The cycling switch is in the system to prevent the compressor from being damaged from operating with too low a pressure. There is also a high pressure cut out that will disengage the compressor if the pressure is too high. Do not bypass the cycling switch or risk damaging the compressor. If something changed quickly, there may have been a line cut or deteriorate to release enough pressure to atmosphere to disable the system. Get it checked for leaks. The high pressure tap was probably just not tightened over the old R12 screw fitting and needed to be tightened. I responded to your personal email, but didn't have the info about the R134a upgrade.

 

[drdave]

Scott,

You're exactly right. The problem that sent me back to the shop was that they did not tighten the high-pressure tap appropriately onto the r12 screw fitting, allowing some r134a to leak out.

But they have recharged it and it is still only blowing out at 60 degrees at the center vent. Do you agree that 350 on the high side is dangerously high?

 

[sdpatt]

There is a high pressure relief valve on the compressor outlet that will vent excessive pressure before it gets dangerously high. Depending on the ambient air temperature and the temperature of the engine compartment, 350 psig may be closer to normal than you might think. If you measure the system pressure at idle in the morning with the engine still cool, the temperature will be much lower than in the afternoon withthe engine hot. from you email, it sounds like your cooling fan is not running. Most likely the motor's brushes are worn out, but you need to verify power to the fan. The motor is $68.87 from FordPartsOnline.com so you can shop around to try to better this price.

Scott

 

[shojuan]

Would anybody in the bay area be willing to lend me a set of guages and a vacuum pump? I did the conversion with the Interdynamics kit two years ago and it works, but not really well. I vacuumed it out with one of those lab style vacuums that attach to a garden hose, then I added the adjusted amount of R-134A. I was in a hurry because there was no R-12 left in the system and the dog needed to stay cool while driving through the central valley at 100+ temps en route to San Diego. Of course the CPS crapped out in the fast lane up the grapevine at 90 mph. Coasted to the right (miracle we didn't get hit), parked under a tree and waited half an hour before the car would start. It limped half a mile and died, waited another half hour, then it made it half a mile to a rest stop (luckily there was one there). We waited about three hours at that rest stop while our german shepherd dog barked and lunged at every dog there (he has hungry ) Then the SHO made it to San Diego and back a few days later. Still have the same CPS and water pump in there but not for long!

BTW Scott, I ordered wires and some sensors from FPN (the AWA is going to be going off any day now ) I just hope the knock sensor doesn't crap out on me after I'm done with the 60K because that is one sensor I did not get (FPN was out of stock and fear of the AWA held me back).

Rick