I set up the gauges with the engine off and the pressures were,

Low side 40 psi
High side 40 psi

I started the engine and the compressor was running. The doors open and the A/C on it's highest setting. The outside temp is 91 degrees and the engine had not been started today, or it was cold. The A/C was blowing ice cold air inside the cabin for five full minutes and did until the compressor clutch stopped turning.

After running five minutes with a slightly elevated RPMs, the pressures were

Low side about 85 psi
High side about 80 psi

After the five minutes the compresor cluth cut off due to the problem I'm trying to understand.

Any A/C experts care to clearify the readings and advise to this A/C novice?

 

the 40-40 means nothing the system is off so it equalizes.
i don't quite know how your suction side could be higher than the head pressure with the compressor running?
I would jump out the low pressure switch and feed it some refrigerant, them see if the compressor will keep running.

 

I'm going under the RR today to jump the low pressure switch.

I understand the 40 hi and 40 low does not ID a problem. The equal 40 pressure with the engine off ---- doesn't this indicate that the A/C system doesn't have a freon leak?

I'm trying to also ID what does work along with IDing what does not work. Any further suggestions? I'll keep researching and post my findings.

 

If the pressure is the same before startup, 40&40, and after running 5 minutes with the compresor running the pressure is 80&80, would that indicate a stuck open Expansion Valve?

Still just guessing at this point, but determined to see it thru.

 

I jumpered the low pressure switch just now but it made no difference. The compressor did not come on at startup this time like it did two days ago.
Does that mean the low pressure switch is good?
I did not connect the gauges this afternoon because it started raining right as I got started and all I have here is an open carport.

I did pull off the Trinary switch and reconnected it twice just to make sure the connections were good.
I could barely see the trinary switch wiring plug. Could a bad trinary switch cause the compressor to not engage or cutout. Two days ago the compressor came on as soon as the engine started, today it didn't come on at all, even after a restart.

There is not a plug-in wire at the compressor on this 1998 RR, just a red wire and a black wire going down into the clutch assembly.

Can I hotwire the compressor to test it's operation now or should I check something else first?

Thanks for any help I can get.

 

Today it's beautiful outside, about 77 degrees and sunny here in south Louisiana.

The RR had not been started in three days so I decided to connect the Manifold gauges to retest the A/C system pressure. Last time the compressor clutch refused to come on even after a 10 mile run.

Today, as I started the engine, the compressor clutch came to life. After a few minutes it cut off like it had been doing last week, but this time it came back on and ran for a couple of minutes and cut off again. But it came on again and all the while the A/C was working great inside.

I connected the gauges to check and the pressures were, low side 45, high side 180 at idle.
I ran and got my wife to raise the RPMs a little and the pressure rose on the high side to 200psi. The low side was about 50psi.
Everything was working perfectly, BUT WHY!

While the system was working I stuck a pin in the red wire going to the compressor so I could check the voltage and the readings was only 9.2 volts and the clutch was running.

Several years ago I was having trouble with the A/C in my suburban and that lasted a year or better. Finally the alternator stopped working on a day trip and I replaced it in Arkansas in the parking lot. Since that day until I sold the truck the A/C worked everytime.
I made a garage workshop friend from a friend that hat told me the compressor clutch will cut off if the voltage drops below 11 volts.

This is what's strange today about the RR's compressor power reading. Should it not be 12+ volts to the compressor? Is the clutch not running a low voltage issue?

I hope someone can help me understand the low voltage reading and why everything worked perfectly today and refuse to work last week. Sadly I didn't test the voltage in the past on the RR.

 

I forgot to say,

After everything started working I drove the RR to a small town called Church Point Louisiana, about 20 miles away and picked up a milkshake and onion rings at the Sonic there and the A/C worked the entire trip.

I'm going to let the engine cool down and this afternoon I'll do all the test again and post.

 

I made a second trip, about 15 miles and the A/C still performed great. I delivered two live traps to a friend.

When I got back in the RR the A/C had stopped again. It was working so good so far today, about 50 miles with excellent cold air. On the way home the book symbol was back too.

I connected the Gauges as soon as I got home while it was still running and the pressures were:

Low 118 psi
High 125 psi

Almost equal again. I'm still thinking Expansion Valve, but I would like a second opinion from another forum member, before I pull the freon and change the valve.

Anyone?