Hi all. You guys helped me with my 1988 E150 with a 5.0 single front AC back in March or April 2016. At that time i had replaced all the components with new Ford factory parts except the accumulator and evaporator which i think came from 4seasons. I used Ford Motorcraft YN9 mineral oil and 54 ounces of R12.

At the end of last year year the vent temps began to get a little colder then normal and i also began to notice water in the passenger floorboard. I have the carpet out and haven't replaced it yet! here is 3 or 4 months later and the compressor is short cycling this spring and no cooling. I was guessing that there must be a leak but when putting the gauges on the high hand low side, there doesn't appear to be any suction on the low side gauge. I had tried to add some freon but it would not take any. I jumperd out the pressure switch and it still would not take any refrigerant. While the switch er was jumpered out, the suction pressure slowly began climbing and was close to even with the high side.
I disconnected everything and then thought I should reconnect the gauges and take some readings.

With the pressure switch connected back as it should be so the compressor would short cycle,
The high side on the R12 scale during short cycle would go from 90-104. on the outer PSI scale it was 100-118
The suction side was around 38 on the R12 scale and 35 PSI on the outer black scale.

The outside temperatures today were around 70 to 72F

Thanks
Any and all help is highly valued!
Annaleigh

 

First, make sure your gauges are actually working correctly. Turn both valves on the manifold fully closed and then connect the couplers to the test ports.

With the system OFF and stabilized, both sides should read exactly the same pressure. If they don't there's something wrong with them. When the clutch engages, the low side should drop while the high side should rise.

Verify basic behavior first. The, diagnostics can proceed.

 

Thank's for the reply and advice.
i connected the gauges as per your advice and with an outside temperature of 67, the pressures were equal at 62 on the R12 scale or just under 61 on the outer black PSI scale on both the high and low side .

What scale do I need to be using when giving you pressure readings?
All of these readings will be using the r12 scale.

I started the engine (everything cold from sitting over night) and turned the AC on to max but low fan.
high side. compressor engaged at about 75 on the red R12 scale. The compressor would cut out at to about 86 on the r12 scale. The cycling was off for around 15 seconds and on for about 3.

The suction side would drop about 2 psi during each cycle bouncing between 43 and 44 psi. The drop started just about the time the compressor cut out and would raise back to 44 just before the compressor cut back in.


So after letting it sit and cycle like this and the engine began to warm up a little, the pressure began to change a little
High side went to 88 to 98 during cycling
low side went from 40 to 38. the drop on the low side was only after the 2 to 3 second cycle of the compressor engaged


50 or 10 minutes later with the engine even warmer the high side was reading 90 to 102 during cycle while the low side stayed around 40 to 38.

one thing I did do while the engine was just starting to warm up was to jumper out the clutch pressure switch. This time the suction pressure started doping and went to 0 on the outer PSI scale which i just noticed is -20 on the r12 scale.

Note. when first turning on the AC with the engine cool. the suction line at the accumulator started getting cool to the touch. that didn't last long though and then it started getting ambient temperature. When i used the jumper, the suction line again got a little cool fro a short time.

When i cut the engine off, it took some time but eventually the pressures equalized out around 90. of course everything was much warmer at that time.

Ok well help some of this is of use.. I have to go to the supply house and buy a set of hose end seals as I lost one from the yellow hose!

Again thank for your time an help.
Annaleigh

 

The one that says "PSI". It's independent of refrigerant type.

Compressor short-cycling is almost always caused by low refrigerant charge.

 

What would cause it not to suck in refrigerant? In the morning I was thinking to connect the gauges and jumper the clutch switch to try to reproduce the suction pressure i had this morning and then try to add some r12.

i will convert the numbers to PSI for you.

 

This morning with an ambient temp of 67F, both gauge equalized at 62 PSI with the engine off

Starting the engine and turning the ac on to max but low fan.
Cycle time was 3 seconds on and 15 seconds off.
High side pressures were 75 to 95 PSI
Low side pressures were 39 to just over 40 PSI

After engine warmed up a little.
Cycle time was 3 seconds on and 15 seconds off.
High side pressures were 80 to 90 PSI
Low side pressures were 38 to 40 PSI

A little while longer with engine up to temp
Cycle time was 3 seconds on and 15 seconds off.
High side pressures were 95 to 115 PSI
Low side pressures were 35 to 37 PSI

When I used a jumper at the clutch switch, the suction side pulled down to 0 PSI at which time I pulled the jumper.
The high side went up to 115 PSI while the suction was at 0 PSI


yesterday I had called a local radiator repair shop to see if they had a way to flush the condenser and evaporator if i found the compressor to be bad. The guy said to bring the van to them and they would check the pressures. They wanted to jump right into it and convert the system to R134a. Their plan was to dump the r12 and refill the system with R134a and a dye. I was to come back in a week or so and they would find the leak.
I ask about the mineral oil and he said it wouldn't be a problem at all.. That is now what I have ever heard. Everything I have read from reputable sites says to try to remove as much of the mineral oil has possible. That would include pulling and draining the compressor. perhaps filing the compressor with pag oil, turning it a few times and flushing it out again but using pag oil. The accumulator would be replaced as well as the orifice tube. The manifold hose that connects to the compressor has a suction line and liquid line built together but there is a muffler on the high pressure line. I have read that you should not flush a muffler. So that would leave the condenser ad the evaporator. The condenser is the old style round tube type so it could possibly could be flushed but i read that is is imperative that all the solvent is removed. That would leave the evaporator. I have read that a little mineral oil will not hurt and will settle on a lower place in the system but that far into it, it would be very dumb not to go a head and pull it out and flush it or replace it.

What are your thoughts... I would really like to just keep the R12 but seems that no one around here wants to pull it out and save it. One place said $100 a pound to put it back in!

 

Seems to me if changing all those parts just to accommodate the R134a is more work that simply finding a shop to re-charge your existing system with R-12.

From what I've read across the internet converting from R-12 to R-134a is usually unsatisfactory to the vehicle owner. Yeah finding R-12 is a hassle but seems worth a bit of effort to have A/C that works as designed.

I suspect your compressor has failed---hope not but good luck with this anyway Annaleigh!

 

I doubt there's anything wrong with the compressor. All signs suggest a low refrigerant charge.

 

Thanks for the replies folks!
So this morning while the temps were still below 70F I connected the gauges and installed a jumper in the clutch connector so that the compressor would run continuous.
The low side went down to -15 so I opened the low side valve to see if it would take some refrigerant. As soon as I cracked the valve the low side pressure started climbing back up towards 60 or 60 PSI so i closed the low side and let the pressure drop back down to 0 PSI. At that point I just barely opened the low side valve till it reached about 10 PSI and tweaked the valve so it stayed around 5 to 10 PSI. At one point I placed the R12 can on the radiator hose to get the can warmer. Eventually I was able to get about 10 ounces into the system.

At the very beginning I noticed the suction line was starting to sweat a little like it did the day before. I put a thermometer in the vent and had the fan on low. While trying to get the system to accept the refrigerant, i checked the vent temp and it was about 50F. Shortly after though with the engine and radiator heating up the condenser and other components, the suction line became warm and the vent temps went back to ambient temperature of around 70F

The compressor is noticeably louder then it was last year . With the extra refrigerant in the system the compressor is cycling even shorter, about one second

The high side pressures are 105 to 125 PSI
The low side is now bouncing 36 to 39 PSI
The readings were taken with the engine up to temp and the ambient air temp about 70F

To me is almost acts like a restriction because the suction side will go into a vacuum but if there was a restriction, the high side would be sky hi wouldn't it?

It had pressure in the system when I started this and it was short cycling. Seems like adding the better part of 10 ounces would have lengthened the cycle time.

What can happen when a clutch cycle switch goes bad? Can a short cycle pull the suction down that fast to where the cycle switch will cut it off but the gauges only register 2 to 3 PSI difference? BTW If I remember correctly, the cycle switch was set just a little lower then spec. I believe around 23PSI
Thanks
Annaleigh

 

so what should I do next?

To save using up the R12, can the r12 be removed and then vacuum the system, temporarily fill it with R134a and run just long enough to see if it will cool and check for leaks?