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HELP! Puzzled with complete new system!

vcp90 on Fri June 17, 2011 12:42 AM User is offline

Year: 1988
Make: ford
Model: ranger
Engine Size: 2.9
Refrigerant Type: r134a
Ambient Temp: 83
Pressure Low: 10-15
Pressure High: 250+
Country of Origin: United States

My 88 ranger had a/c at one time but the previous owner ripped everything out but evaporator.

I replaced every single component including:
Remanufactured Compressor (Fs-6 ready-aire)
all refrigerant lines
orifice tube
all new green orings lubed with blue nylog
new low pressure cut off switch

Okay, so heres what happened. as you just read i put in a complete new a/c system. the orifice tube i used was a variable orifice/smart VOV.

I vacuumed for 1 hour and verified it held 30 inches overnight. I added 8oz of Ester oil to the compressor and drier before buttoning it up.

when i went to charge it, i know the variable orifice can be a little screwy with charging by weight(still had r134 cylinder on scale anyway), and i heard its better to watch vent temps also whilst charging. i had a digital thermometer in there.

with vehicle at about 900rpm i started charging. when there was about 1lb 5 ounces or r134a (r-12 oem specs are 2lb 2oz) the vent temps werent getting any colder at about 43 degrees. at this point the low side was about 40 and high was like 230. as soon as i raised the rpm over 1000 the low side went way down and high went well over 250. when it hit about 280-300 something was causing the compressor to be hard to turn(almost seize up and the clutch would screetch like crazy). so i recovered some of it down to about 1lb or less and the low is at about 15 psi and high is 250-260. at this point at idle vent temps were 60, and at 2000rpm with fan on condenser they were 54.

i thought there was a problem with the variable orifice so i recovered everything and put in a new ford red fixed orifice. basically the same issue, maybe a hair better. i got about 1lb of refrigerant in and at 2000 rpm the high side is pushing 250 with the low at 10-15 (had to adjust screw in cut off switch to get it to run that low). this is where im at now.

i cant figure out what could be faulty. i know it should have at least the 1lb 5oz because the air is ice cold at that that charge but anything over idle and the high pressures climb all the way 300+ psi till the compressor starts to lock up. the only way to prevent the pressure on the high side from going through the roof is to only charge it about 15-16oz of r134a. and still the low is like 10-15 psi so that charge cant be right at all. what is going on here! is the remanufactured compressor bad?

any help is GREATLY appreciated.

mk378 on Fri June 17, 2011 7:26 AM User is offline

Compressor works great to make all that pressure. I don't see any mention of pulling a vaccuum before charging. That is essential as air in the lines does not condense, and builds excessive pressure.

Also make sure you're using the right kind of oil and the right amount. A compressor ordered for a 1988 may come filled with mineral oil under the assumption that you'd be using R-12.

Assuming you did evacuate first, the fan clutch is probably shot. Fan will still spin, but not as fast as it should. Put in a decent charge and road-test at 30 mph+ so you're getting air through the condenser without needing the fan. If you're building a new system and gong to run R-134a you should try to fit a parallel flow condenser instead of the stock type. The VOV never worked well just use a fixed one. An orifice that is smaller than stock can help keep pressures down. The compressor should cycle off when the low side goes below 20, check the cycling switch and electrical circuit.

Edited: Fri June 17, 2011 at 7:30 AM by mk378

vcp90 on Fri June 17, 2011 3:23 PM User is offline

I vacuumed for 1 hour. Let it sit overnight. Was still 30inches in the morning. I vacuumed it for an extra 15 minutes before i charged it
I put a shop fan over the condenser, and tried the garden hose. It didnt really change much at all. Maybe dropped 2 or 3 psi.

Im pretty sure it is paralell flow as there are no tubes on the sides. I thought there were two types: paralell and tube and fin?

I adjusted the screw on the switch so it would cycle at that low of a pressure

Could the cheap aftermarket condenser be the problem? A faulty internal restriction?


Edited: Fri June 17, 2011 at 3:25 PM by vcp90

mk378 on Fri June 17, 2011 3:53 PM User is offline

A tube and fin has lots of u-turn tubes at each end. There is one path through the pipe which goes across, turns around and comes back over and over again. A parallel flow typically has manifolds on the ends that look like vertical tubes with plugs in the top and bottom.

vcp90 on Fri June 17, 2011 5:04 PM User is offline

Ya it is definately a paralell flow. There are no tubes and at the four corners there are what look like little tiny freeze plugs.

I have a tube and fin on my other factory ac truck and that condenser design looks way more efficient. I might be wrong.

I ordered a used oem one off ebay. When that comes i will give it a try. All the oem ones are tube and fin.

Could it be that r134a is already less efficient than r12, and r134a has a higher head pressure to begin with so it needs a really really good condenser,and a parelell flow is less efficient than the stock tube and fin, plus the fact the cheap $40 brand new chinese condenser is probably clogged/internally restricted/piece of junk, be the problem here?

Thanks so much for all your help

Edited: Fri June 17, 2011 at 5:07 PM by vcp90

TRB on Sat June 18, 2011 5:09 PM User is offlineView users profile

Don't just bag on the china products. I've seen some crappy condensers from US suppliers in the past. Looks under charged from the get go. With the proper amount of refrigerant. I bet you see an elevated high side. Needs a true parallel flow multi veined condenser. Toss the VOV in the trash also.


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bromodragonfly on Sat June 18, 2011 8:13 PM User is offlineView users profile

Kind of a tough guess since your system doesn't have factory matched components. I think I would try a bigger orifice size before buying a new condenser. The fact that the system runs fine when you're idling tells me that the condenser must be cooling that gas into a liquid, and that orifice is working when the pressures are lower.

When you rev your RPMS up, both sides of the system should rise in pressure. But the opposite is happening on your low side. It sounds like you're having a back up of liquid in your condenser, at the orifice, and since it's not feeding enough liquid into the evaporator to keep up with the compressor, the low side is starving. That, or some kind of other restriction in the low side.

The horrible screaming/seizing with your compressor is probably the discharge gas pressing back against the discharge valve. It could be bypassing a check valve, if there is one, or it could be trying to push the scroll or rotor backwards. Plus, since the low side pressure is so low, the little vapor coming back to the compressor is probably highly superheated.

If you hook up your gauges and can get a strap-on thermistor to read temperatures, you could calculate your subcooling and superheat based off of the PT chart for R134A.... I usually find this is the best way to get a good idea of what is happening in each component of an AC system. Temp at condenser outlet, compared to saturation temp at high side pressure, will let you know how much subcooling your condenser is providing. If that drastically improves with a huge fan and running cold water (forced conditions that will not occur when you're driving), well, maybe the condenser is the weak link.

But since it has good normal operation at idle... I would try the bigger orifice for now

There is no knowledge that is not power

vcp90 on Mon June 20, 2011 11:42 PM User is offline

i will try the orifice swap. i ordered a blue ford one which is bigger than the red ford in there now. i also ordered a 1250 cfm condenser fan w/ relay and i will power the relay with the compressor clutch power so the fan is on whenever the compressor is on.

i also ordered a used oem condenser for backup if it comes down to a restriciton in the condenser.

i will check the inlet/outlet temp drops and calculate superheat tomarrow to try and figure out what the problem is while im waiting for those parts to come.

is there any chance at all it could be caused by a faulty compressor? maybe a faulty reed valve or something? i am not very familiar with the internals of the compressor. it is a ford fs-6. also is there any chance the reciever/drier could be faulty? it was brand new, had vacuum in it when i pulled the plugs out. and was in a sealed bag. it was installed last into the system and the system was vacuumed down to 30 inches within 5 minutes of taking it out the package.

thanks guys

basically, these are my options:

i will have the following to try: i have a used oem condenser on order, i have a used fs6 compressor, i have a 1400cfm electric condenser fan on order, a 10 pack of red orifice tubes (what im using now) and a 10 pack of blue on order.

order of trying stuff (continuing only if prior step didnt do anything) (feel free to give me an idea for a better approach)

1. put the new fan on the system as-is
2. evacuate, swap in a blue orifice tube, and charge
3. evacuate, swap in used oem condenser, and charge
4. evacuate, swap in used compressor, and charge
5. take off all the used parts, swap in the new parts since the new parts are now all known good parts, put the red orifice back in, and charge with 40oz of r12 as last resort.

i have 3 cans of r-12 i was planning on saving forever. two 14oz and one 12oz, which turns out to be 40oz, the exact factory r-12 refrigerant amount, but i wanted to save this and use it as a complete last resort.

Edited: Tue June 21, 2011 at 12:46 AM by vcp90

bromodragonfly on Tue June 21, 2011 7:00 PM User is offlineView users profile

Try that bigger orifice and let us know if it helps. Make sure it's pointed the right way.

If it doesn't, come back with pressure/temp readings and I'll look at the subcooling/superheat for you to try and figure out wtf is going on.

Take a high side pressure reading, and take the temperature at the compressor discharge line. Take the temperature at the inlet of the condenser, and the outlet.

Take a low side pressure reading, and take the temperature at the evaporator inlet, and outlet.

Take note of ambient temperatures at the time, as well as temp of air blowing out of your vents.

Temperature at inlet and outlet of receiver/drier should be the same. If the outlet (or the receiver itself) is significantly cooler, it indicates that the receiver/drier is acting as a restriction.

I don't have much experience with variable displacement compressors (if yours happens to be one), but usually a valve problem will result in lower discharge pressures and extremely high superheat directly after the compressor.

There is no knowledge that is not power

vcp90 on Wed June 22, 2011 10:31 PM User is offline

alright. today i replaced the red orifice with a blue one, and installed the 1400 cfm puller fan on the condenser. put in 18 ounces of fresh 134a the system is awesome now, but the low side pressure stills seems a little wierd?

here is what i got with system running at high idle for 10 minutes. (farenheight)

Ambient: 76 degrees
Vent: 41 degrees
High: 155 psi
Low: 14-17 ( i have a fluctuating idle: 300,000 mile engine)
Rpm: 1100-1200
Evap inlet tube temp: 38 degrees
Evap Outlet tube temp: 41 degrees
Cond inlet tube temp: 130 degrees
Cond outlet tube temp: 103 degrees

it seems the low is still low. if i bring the rpms up to 3000+ the low side stays the same and the high slowly climbs to about 200. if i unplug the fan the high side instantly goes way up.

ive had the blue orifice in there since yesterday, but the big fan came today. now, i know 76 is not very hot out, but it was 100 degrees ambient yesterday and i tried the same thing with a much smaller transmission cooler fan. even then after about 10 minutes the temps were 45-49, and the high side never went over 260 psi as long as the fan was on.

now today i actually drove it through town (was about 73 out) and the vent temps fluctuate from about 39-43 degrees. awesome!! its so cold it hurts!

im just still wondering why the low side is still so low? when it is on the evaporator outlet and the accumulator are ice cold and have condesate all over them, which eventually turns to frost. is that also bad? the pressures dont change when there is frost so i think its okay?

thanks guys

mk378 on Wed June 22, 2011 11:07 PM User is offline

Again, that low side is because you messed with the switch. It should be cycling off instead of letting the low side go below 20. Frost may eventually form on the fins of the evaporator, which will block the airflow and preclude cold air from getting to the vents. That's the point of the cycling switch, prevent over-cooling and ice-up.

You should get the engine fan working stronger. I don't see any mention of a new fan clutch. If the fan shrouds have been removed, replace them. A properly-working engine fan on a truck has a lot more power than electric fans ever will. I think you may still be undercharging because of the poor condenser performance.

Edited: Wed June 22, 2011 at 11:11 PM by mk378

bromodragonfly on Thu June 23, 2011 12:19 AM User is offlineView users profile

Yeah, dial that switch back up to around 28psi to maintain just above freezing in the evap.

Your condenser outlet temp for 155psi discharge is just at the saturation temp, not much subcooling. This could change once you bump your LP cutout to where it should be. You're running too low right now - the frost on your suction lines/accumulator is a sign that there is still liquid coming out of the evaporator and boiling off. Once you get the evap to a normal pressure, you may be looking at higher discharge pressures and temperatures, and you'll definitely want to take another reading at your condenser to see if it's still keeping up.

In a nominal system, the refrigerant leaving the evaporator should be 100% vapor and superheated by a couple degrees.

If you leave the pressure switch as is, you'll ice the evaporator up. And you could risk ruining your compressor with liquid slugging.

And MK is 100% right about airflow over your condenser. You'll definitely want to maximize the efficiency on that beast.

There is no knowledge that is not power

JJM on Thu June 23, 2011 9:58 PM User is offline

Just an FYI, according to Ford TSB 98-4-8, retrofit on your vehicle calls for a condenser, fan enhancements, and misc parts kit which includes, CPS, CPS adapter, RCS, RCS wiring harness assembly, RCS adapter, low side service port adapter, high side charge port adapter, PAG oil, and retrofit label.

If you're using the stock tube and fin R-12 condenser, you don't have enough condenser for R-134a, you need a parallel flow - as much as you can get in there. And don't be afraid of slightly higher discharge pressure on a retro - it's just an indication of not enough condenser. Never undercharge to get acceptable high side pressures, or you risk the possibility of starving the compressor of oil.

Over 300 PSI even on older R-12 systems is normal when the ambient gets way up there (100F and over), so don't fret on a R-134a retro.


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vcp90 on Wed June 29, 2011 7:53 PM User is offline

thanks for all the help guys. the system is perfect now. i added a couple more ounces and everything is right where it should be

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