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Help with this faulty compressor diagnostic?

nitz on Tue February 12, 2013 2:12 PM User is offline

Year: 1998
Make: Ford
Model: Mondeo
Engine Size: 2.0l
Refrigerant Type: R-134
Ambient Temp: 90ºF
Pressure Low: 40
Pressure High: 150
Country of Origin: Brazil

Hello, I need some help with my car, it's a 1998 MK-2 Mondeo with about 27.000 miles, it's has been mostly as a back-up car since 2005.

The A/C performs really poorly during hot weather, the compressor runs all the time except when it's turned off by the throttle sensor (about 80% I think).

Low side pressure was about 15 PSI and high side 150 PSI when I decided to refill it, only the low side pressure got higher to around 40 PSI while the high side persisted the same and didn't get any higher, the compressor still runs all the time and the air is not cold enough during hot days, the temperature coming from the blower is about 75ºF whilst at night or slightly cooler days it works surprisingly well.

I took the car to a local ford dealer and I was told the A/C compressor and accumulator/drier filter needs to be replaced but I'm not really buying their diagnostic since this car has been mine since new and it has a very low mileage.

Could this be the expansion valve? Should I vacuum the whole system and try to fill it again with the 740 grams recommended by the sticker under the hood?


mk378 on Tue February 12, 2013 2:34 PM User is offline

Charge by weight first is essential for a proper diagnosis. Post the compressor model number if you can find it. It may be a variable compressor. Those, by design, run all the time.

nitz on Wed February 13, 2013 4:42 PM User is offline

Ok, I did fill the 740 grams of R-134 as recommended by the manufacturer after removing all the previous refrigerant through a vacuum pump.

Still working exactly like before but the pressure readings are far different.

Ambient temperature about 90ºF

Car off: High 100 PSI, Low 100 PSI

Car idle: High 200 PSI, Low 60 PSI

@ 2.500 RPM: High 350 PSI, Low 55 PSI

The compressor is quite noisy while working, however all the pulleys are running all the time and I'm pretty sure the noise is coming from the compressor, so there must be some damaged clutch bearing or something, it still cools just fine when not directly under the sun or the outside temperature is below around 82ºF.

I can't get to the compressor right now since It's hard to reach but it's this one.

Edited: Wed February 13, 2013 at 4:45 PM by nitz

NickD on Thu February 14, 2013 6:37 AM User is offline

Noted a huge difference between Latin American vehicles and those sold in the USA, for one thing, most countries down there, least for us, have no EPA to deal with.

If you are using PAG, still have to flush out the system, drain and flush out the compressor, replace the receiver or accumulator, draw a deep vacuum and inject the correct amount of PAG. If someone just added a couple of ounces of PAG over the last 15 years, can have too much oil that could be causing your problems.

First step in AC repair is cleaning up the system, find condensers and radiators loaded with bugs, blower fan works more like a leaf chopper jamming up the evaporator core. Can't have air conditioning unless the air flow is good, also produces high pressures with poor cooling.

These are all basics, sure the same thing holds true in Brazil. Wife is from Venezuela, they have 365 days of summer down there. I can't believe the cost of parts down there, I thought they were bad here. Over a hundred bucks for a drive belt! Over a hundred bucks for a cheap made in China six piece combination wrench set!

nitz on Thu February 14, 2013 8:28 AM User is offline

Thanks for the advice,

This Mondeo was manufactured in Belgium and came over the seas in the 90s.

I will purchase a new accumulator from Amazon in the US(Mystique/Contour/Cougar) since the local Ford dealer sells it for over U$500. And someone has probably added extra oil from previous refrigerant recharges, I've no experience with automotive air conditioners but I don't really trust the local garages to do the job, plus they charge too much for the parts, labor not included.

Then I'll finally take a look at everything including the compressor itself.

Is there any way to know the right amount of PAG? The service manual doesn't mention anything at all.

Edited: Thu February 14, 2013 at 8:39 AM by nitz

NickD on Thu February 14, 2013 10:00 AM User is offline

They have what they call a cadivi or something like this, where Venezuelans are permitted to just buy a few US goods per year at the so-called fair exchange rate. We want to send a new baby stroller to my wife's son, shipping cost alone is 450 US, bucks. Wondering if your country is that way too.

nitz on Sun February 17, 2013 5:35 PM User is offline

Honestly I have no idea how to legally import stuff from the US without hassle and paying absurd taxes however my aunt is American, thus makes everything easier.

On a quick and small update, I will try to bypass the heater water because the air coming from the A/C blower without the compressor running is rather warm-hot, I'll see if it makes anything better, if positive I might add a manual valve to control the heater operation.

I couldn't really test it before since my A/C button was broken and I couldn't turn the A/C off and leave the fan on.

NickD on Sun February 17, 2013 11:01 PM User is offline

In the American cars, a blend door is used, heater core is always hot, and blocking it could burn a hole in the engine. Only way to get around that is to bypass the heater core.

All the air flows through the evaporator core then depending on the position of the temperature control lever some it all of it goes through the heater core, rest goes through an unrestricted vent. Some of these older Fords used a a kind of a slip clutch in the blend door cable, all you had to do was to swing that temperature control lever to the far right, then the far left to adjust it. Unless that slip clutch was worn, then it had to be replaced.

Have no idea what your car is using, but did want to caution you about blocking the coolant flow to that heater core, you may burn up your engine. Heater core manual valves are kind of history around here.

ice-n-tropics on Mon February 18, 2013 6:18 PM User is offline

Dealer has head squarely up his whats'it.
Your link to the Ford compressor page didn't work for me.
The comp pumping performance is OK w/ 350 psi discharge and as low as 15 psi suction.
The compressor rotor pulley bearing rarely goes out, but if it does, look for wobble because the new spec is 0.015" TIR max.
Comp is often noisy if charge amount is wrong or air is inside system. Suction pressures should be lower, therefore, look at expansion valve. Sensing bulb, if equipped could have poor contact w/ suction line tube.
Service could have introduced non-condensible air into the A/C.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

NickD on Tue February 19, 2013 10:17 AM User is offline

Stepgrandson needs a stroller, 150 bucks here for a real nice one, but 450 bucks for us to ship it down there. My own kids have some very expensive strollers, hardly used they are more than willing to donate, but then the shipping cost between here and Miami is also outrageous, cheaper for me to order a new one on line and have it dropped shipped to Miami with free shipping. A new one down there is over a thousand bucks, what's with these Latin American countries?

We are not without our problems here with all this recent crap imported from China, never was trained how to repair crap. Maybe this is my problem. Ball bearings in particular, really have to search hard for bearings made in Japan, Canada, or the USA.

Z2TT on Fri February 22, 2013 6:53 PM User is offline

The Low Pressure side seems way too high, only 5 PSI drop from Idle to 2500RPM.... Perhaps the TXV could be faulty.

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