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air conditioning diagnosis

10K views 51 replies 15 participants last post by  MRDANGERUS 
#1 ·
The a/c on my 1995 S4s is not cooling. That is the R134 system like a V8. We evacuated the charge and refilled with the proper amount of 1kg. With 1kg in the system we got normal high pressure but zero on the low pressure side. If we overfill the system we get a bit on the low side but not much and the compressor cycles rapidly, not surprising. There are no leaks, it holds vacuum just fine.

This sounds to me like a blockage. The service manual doesn't have much info. Is there an inline filter? Might a bad receiver/dryer cause this problem? I hate to look at the evaporator given its almost impossible to get at, and the normal failure mode for an evaporator is a leak, not a blockage. Is there an expansion orifice that is serviceable?

Any air conditioner experts here?
 
#33 ·
From Section PJ in the service notes:

International legislation banning the use of refrigerants containing ChloroFlouroCarbons (CFCs) resulted
in a change from refrigerant R-12 to R134a occurring in mid 1995 at the following change points:
S4 approx. S 2017
S4S approx. S 4002
USA S4S approx. S 3012
Sport 300 approx. S 8058
(Note that all V8 models use R134a)
 
#34 ·
Following up on my old thread. It worked for almost two years with a bit of extra R134 in the system, but the blockage has returned. No doubt I need to replace the orifice.

Question: How do you get to that bugger, it seems to be buried in the dash?
 
#36 ·
You don't have an orifice tube per se, it's an older type expansion valve. It's not easy to get to but is accessed in the passenger side footwell and is wrapped in black gooey insulation tape right at the evaporator. Remove the seat and assume the Lotus position. You'll have to unhook a couple of vent duct pipes IIRC. It's not a pleasant job to remove and replace the expansion valve but doable in an hour or two. Be sure to replace the insulation tape or you will have condensation dripping in the footwell later.

That being said, as exigegus said, did you try adding refrigerant?
 
#37 ·
Jim, thank you for the heads up on the location. Yes its an expansion valve, I used the wrong word. If you read earlier in this thread this problem has been going on for quite a while. Its gotten worse now, to the point where we have lots of pressure in the high pressure side, but none in the low pressure side. It works occasionally but not for long. Definitely a blockage somewhere.
 
#38 ·
If the system runs OK at first but the high side pressures climb and the low side pressures drop that is often because there is moisture in the system and it freezes up in the TXV eventually blocking it entirely. The cure is to remove the refrigerant and evacuate the system. Evacuating the system means using a vacuum pump to pull the air out and then boil out any moisture. In a system that has moisture (or has been open to the atmosphere for a while), good practice is to replace the dryer before evacuating and refilling. Any good A/C shop should be capable of fixing this. You should not need to replace the TXV but it can't hurt to remove it and clean it up.
David Teitelbaum
 
#40 ·
I would guess it doesn't matter, although I'm admittedly not 100% familiar with the Stevens model HVAC system. In general the purpose of the copper tube is to regulate the flow of refrigerant through the evaporator. You don't want the temp of the evaporator to drop below 32 degrees F or condensation will begin to freeze on the matrix eventually blocking all the airflow. As the temp of the evaporator approaches freezing it tells the expansion valve to slow the flow of refrigerant so the temp won't drop to freezing. As long as you can get the bulk of the copper tube, especially that coil on the end, in the proper place - directly behind the evaporator (downstream of the airflow), it should work fine.
 
#42 ·
Not knowing the specs of the original and your cross/over it is impossible to say if it will work. It may work but just not give you the most performance since it may not work at the same specs. Many places will give you something that fits but the pressures and temps the valve will open and close at are not the same. The coiled small copper pipe with the bulb at the end has to be attached to the outlet (suction) line to measure what is called "Superheat" and basically prevents the evap coil from freezing. After attaching the bulb it should be covered with insulation to prevent the ambient air from getting to it. Test for leaks before covering it up.
David Teitelbaum
 
#44 ·
What was your source for the proper two-tube thermal expansion valve?

If there is an updated cross-ref number, let us know. :UK:



At least, a properly working S4s A/C system will not create Freezing Knee Syndrome, as the earlier vent configuration does! :clap:
Our '88 is ready for the Lotus Owners Gathering in Cleveland in two weeks...my right knee shivers properly after only a few minutes of A/C! :D
 
#46 ·
What was your source for the proper two-tube thermal expansion valve?

If there is an updated cross-ref number, let us know. :UK:
Four Seasons / Everco part number 38604
I bought it on Amazon for $18.64

I'm not expert on these things but I've been told if you replace it with a single tube valve it will work but that could contribute to the freezing over problem that some have reported. I drove the car this last weekend, it was 90F and humid. Plenty of cold air out of the system.
 
#47 ·
A/C COMPONENTS

I am working on getting my air conditioning in order for the trip to LOG38 in a few weeks. I looked at the air dryer and expansion valve and low pressure switch to replace as part of the service. SJS has the parts in UK and after getting a price from them i looked at Advance Auto and Napa and the prices looking at a few different sizes are over a hundred dollars less on the dryer alone. Anybody have a recommendation for G-Car. I was not planning on replacing the compressor at this point.
 
#49 ·
What David said. Replacing the dryer is standard if the system has been opened or the system has leaked and has been empty for a while otherwise it can be reused. The others are on a as needed basis. If you have a leak ask your AC shop to put in a dye that will allow you to spot the leaks. There's no magic to the driers. Take your old one to a good AC shop and they should be able to match it.
 
#50 · (Edited)
I saw Don's post #46, in which he shared the CORRECT TXV part number for S4s system running R134a.
Very valuable intel, Don.
Thank you!

Auto part Font Fashion accessory Gas Household hardware

Above, 4-Seasons part 38604.

Now, I have to find out what PO had installed on my car.

Note that PN# 38637 has a reservoir at the end of the probe line, which may make this valve more responsive due to a higher thermal mass.
Auto part Nickel Engineering Cylinder Household hardware



Question to All:
Does anyone know a correct TXV number for the 1988 X180 Stevens car with R12 in the veins?
I'm wondering if the same part can be used?

Thank you
John
Esprit S4s #158 of 158
 

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#52 · (Edited)
I found a section PJ for 89-95 4 cylinder car R134a systems, which says:
If a new compressor is to be fitted and there is no evidence of oil lose
-drain the oil from the old compressor and measure its volume
-drain the oil from the new compressor and discard
-refill the new (now empty) compressor with the amount of NEW oil equal to that drained from the old compressor, plus an additional 30cc. 4.cyl cars require PAG 46 oil.
After a major failure/leak involving a total loss of fluid+compressor replacement, add an additional 80cc of oil to the 175cc(?) supplied in the new compressor.
Never re-use the old oil.
Note: quantities are different for V8 and/or pre-89 4 cyl. cars
Consult your Service Notes specific for your model year.

Note: A transducer on the drier senses the pressure of the refrigerant and should allow the system to operate only within a pressure range:
2 to 27psi Max, for R12
2 to 32psi Max, for R134a

Also, the ignition coils with the base must be removed before attempting to disconnect the large elbows at the compressor. You'll need 27mm and 22mm line wrench.
Bolts holding the compressor to the intermediate bracket are M10 with 17mm heads; nylock nuts measure the same. On re-assembly replace nuts with 15mm hex parts for ease of access/assembly.

Stay cool!
 
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