Finally changed everything out and got the car running (long story and another thread).

Got the charge going last nite with 2+ cans of r-134. High side at 200psi, running the engine at 2000rpm's, got vent temp of 50 degrees. Took a test drive, 20 minutes, ran fine, stayed cool.

This morning, no cooling and compressor isn't cycling, even on defrost.

Any suggestions?

Before filling with r-134 last week (stud broke on thermostat, stalling the process), vacuum was pulled for 3 hours, then another 30 minutes. It held over 29 for over 30 minutes after turning the pump off, so I feel as if the system is buttoned up. 1 can of r-134 went in last week, the rest last nite.

edit: I turned the screw on the low pressure switch 1/2 turn counterclockwise before charging.

 

Hook the gages back up and verify a static pressure (compressor not engaged) of at least 50 psi. That's the threshold that closes the contacts in the Low Pressure Switch. If it has that much, wriggle the connector and if it starts, the connection is intermittent or it wasn't snapped on securely. If it doesn't, jumper the harness with a paper clip. If still no joy - repost with Year and system - Electronic or Manual?

 

I'm at work, so no gauges, but I did try the paperclip on the low pressure switch and the compressor did not cycle.

Also, the low pressure switch is new.

 

I see it's an '85. If Manual air, the circuit is pretty simple. Power from the a/c fuse to the Dash, out to the low and high pressure switches and then onto the compressor with a splice to the ECM. Static pressure, fully charged, should have both switches closed so you can also check them with a meter. If the high pressure switch has opened, it may be bad, but I'd certainly slap some gages on it to be sure (it doesn't open to 400 psi). You can check voltages at the switches too - should have 12 volts.

If Electronic Air, it's bit more complicated. Dash Controls need a completed circuit to the High and Low Pressure Switches. Reference from the Dash is only 5 volts Needs another circuit completed to the ECM - B7 - again 5 volts. Dash then sends a 12 volt clutch signal on a third circuit to the Blower Module (Green Yellow Wire) which grounds the compressor (Green) at the Module. Compressor power is directly from the a/c fuse. Do check the fuse and the switches and that the Module has power (from a fusible link - Red - Battery - though if it didn't have this the blower wouldn't work). Jumpering Green at the Module to ground should engage the clutch and if all the voltages check out, Module is probably bad.

I wouldn't put anymore juice in it. 3 cans is too much and it may have had a tad too much with 2 cans. 50 at the vents isn't great. Is the orifice clean? I definitely get some gages and monkey with it once you get the compressor running again.

 

the orifice tube is new
gauges are at home, car is with me at work

 

Maybe I read this wrong - if the compressor is running and it's hot - check the temp door inside the Evaporator Case. Remove the Module or Resistor Pod and make sure it moves between 60 and 90 (Electronic Air) or Hot and Cold when you move the slider. Electronic controls the door with an electric motor - Manual with a cable.

 

The cable on the Manual selector on my '85 seized up and came off.
It was set on a warm setting.

You can see the door by removing the lower panel on the passenger side, and looking up into the cavity.

 

The compressor is not cycling on at all, even if the low pressure switch is jumpered with a paper clip.

It is a manual, not electronic, climate control.

Something is telling the compressor not to cycle.

 

Compressor shouldn't cycle - turn on and off - at 70 degrees or above if it's charged correctly. It should always be running with an idle pressure of about 28 psi. If you want to check the low pressure threshold, leave it on high and disconnect the blower motor. That should drop it enough to reach the cutoff pressure (22.5 psi is where you want it for R134) and get it to turn off. If it isn't coming on at all, use the info I gave you to troubleshoot the circuit.

 

Shouldn't the compressor cycle if I jumper the low pressure switch with the paper clip?

 

No - cycling refers to a turning off and on of the compressor. A high pressure liquid is metered into the evaporator through a restriction (orifice) changing it to a low pressure liquid. The warm air hits it and as it boils, it absorbs heat. You want that low pressure liquid to boil as close to freezing as possible which for R134 is right around 22.5 psi. If it's lower than that, you'll make ice. SO, the low pressure switch is installed in the compressor circuit to cut the power to the compressor clutch when the pressure is below the freezing threshold. Once the compressor stops, the pressure rises and when it reaches 50 psi on the low side, the low pressure switch contacts close and the compressor starts running again (and will continue to run until it drops below the threshold wherein the whole cycle is repeated). Since the temp of the air at the condensor determines the pressure of the liquid being pushed through that restriction, warmer condensor temps correlates to higher pressures; and on a 70 degree or better day, a fully charged system usually won't drop to the cutoff (freezing) threshold. Now if the compressor isn't engaging in the first place, you can jumper the harness contacts to see if the compressor comes on. That's a quick test verifying that the switch contacts are open and that there's juice flowing in the wires, but gages are a better way to tell what's going on and a fully charged system that's just sitting there should easily have enough pressure to close the switch contacts (ie, 50 psi or more) and the clutch should engage.

If you want to see if the threshold for cutting power to the compressor is right, pull the blower motor connector and the sudden lack of air across the Evaporator core should cause the pressure to drop low enough to reach the cutoff threshold. Note it in on your gage and if it's wrong, disconnect the low pressure switch and turn the adjustment screw counterclockwise to reduce it; clockwise to raise it. Plug it back in, crank it back up to max, pull the blow motor connector again and see if you've got it right. Keep repeating until you do. Otherwise, there are plenty of charts to show what the high and low side pressures should be for any given condensor temp or just post them here and we'll give you our best guess.

 

SunCr-that may be the MOST educational post on a/c I've read. That explains a lot that was lost on me. Thanks for the well written response!

As for an update-got home Monday, hooked up gauges, and no pressure! Had a flyer for my local Firestone dealer with an a/c check service for $24.95. They also do my alignments so I have a good relationship with these guys. Took it into them and they put in a lb of r-134 and some leak detection stuff. Got 50 degrees at the vent.

Tuesday, July 4th, I took the car for a 150 mile round trip. Outside temps of about 80. Got 50 at the vent when it was on max. Comfortable ride home.

Wednesday, July 5th, took car into work, got 56 at the vent on normal with outside temp of about 65. Ran it just to test it.

When I took it into Firestone, the caps on the low and high side adapters had oil inside them. I think one or both might have caused me a leak, since after those were removed, and with the freon added, I've had cool air. I think if this continues, I'm looking at just dialing the right amount of r-134 in there and I'll be in good shape.

 

SunCr, I was reading Scorp's post on his evaporator troubles and you mentioned something about window ribbon tape.

On mine, the outlet pipe from the evaporator has lost its foam insulation through the years, right there at the evaporator box. When the air is going, there is quite a breeze coming out of that spot. Would this tape work for this application? What are the ramifications of that insulation not being there?

 

Works for me - Window Ribbon Sealer - the last roll I bought I found at Pep Boys. I've used it around the Evaporator Housing (including the lines), underneath the windshield trim (it leaked after the windshield was replaced), and under trim around doors and windows in my house. You might want to wear gloves as it's pretty sticky - but it cleans up with denatured alcohol.

 

There was a leak at the connection on the line from the evaporator to the accumulator/dryer, right at the acc/dryer. Changed the o-ring, pulled vacuum, charged. Now blowing 50 at the center vent.