This is mostly in response to several posts where the person posting is apparently unsure of what components are on which (high/low pressure) side of the system. A/C does differ between RWD models, so it is important to relay the CORRECT information about which side of a particular system the components are on. These are basic reviews. If someone doesn't give a definitive amount of information, however, another person will read the advice wrong and end up getting something backwards, or reading high pressure on the low pressure side and overcharging (and exploding) a system. And possibly getting hurt in the process.

For these reasons, it is HIGHLY recommended that anyone who is unsure of what kind of system they are working on, stops and either figures out what it is, or abandons the job until they can figure it out. Also it would probably be good for people who are confused about these differences, to STOP giving advice before someone destroys their A/C or gets injured.

This is a review of systems on the 240, 1983-1990, and the 940, 1991-. The information applies to other models as noted. Models of the 240 BEFORE 1986 ARE NOT COVERED, although some information does apply. The 940 information applies to certain models as noted in the section labeled "940".

Models are listed by VEHICLE MODEL because most of the confusion I have seen, is primarily caused by people applying 240 A/C information to 940 A/C systems. Included at the end of the review is a breakdown by model.

Information on model years is stipulated when known to be true; otherwise model information is suggested as being "possibly earlier" or "possibly all models" because of the inability to verify this information at the time of writing. Model years are included where known.

The purpose of this review is not to include every screw, pipe, and switch in the A/C system, but is merely to educate about the fundamentals of two different kinds of A/C system found in RWD Volvo models from the mid-1980s to 1998. Minor details are not the purpose of this review. Component functions are not included; this review assumes functional knowledge of major A/C components.

Corrections that fall within the scope of this review are invited.


240 Models

Please consult above years reviewed. This DOES NOT cover the 1991-1993 240DL/GL/SE/Classic. Those are 900-type systems; see 900 description for information.

The 240 has a Thermal Expansion Valve system. Refrigerant travels in the following order:

1. Compressor begins cycle at high pressure side outlet
2. Condenser
3. Receiver-dryer
4. Expansion Valve

*** transition from high to low side via expansion valve ***

5. Evaporator cools cabin, picks up heat
6. Refrigerant gas returns to compressor via suction inlet to begin cycle again

The TXV system has the receiver-dryer (small can) on the HIGH SIDE of the system, BEFORE the expansion from liquid to gas at the expansion valve.


940 Models

This system also applies to 700 series cars and 960 models. It also applies to *ALL* 240 models from 1991-1993. The mechanics of the system are the same between climate controlled and non-climate controlled systems; electronics vary and are beyond the information covered in this review.

The 900 system is a clutch cycling orifice tube system, abbreviated CCOT.

The CCOT system cycles refrigerant through the following components:

1. Compressor begins high pressure cycle at compressor outlet.
2. Condenser
3. Fixed orifice tube (locations vary slightly, ALL are high side fixtures)

*** Transition from high pressure to low pressure side via Fixed Orifice Tube ***

4. Evaporator (downstream of F.O.T.)
5. Accumulator-dryer. NOTICE this is on the LOW SIDE
6. Refrigerant returns to compressor via suction side.


The CCOT system has the accumulator-dryer (large silver can at the firewall) on the LOW PRESSURE SIDE. It is suitable to charge into the accumulator, as is plainly evidenced by the presence of a charge valve attached to the same low side pipe adjacent to the accumulator.

Again, it is STRONGLY recommended that anyone who is unsure about the components of an A/C system, avoid work until a time at which they have become sure about it. Damage to the system, and injury can result.

Use of this information is the responsibility of the reader. No liability is assumed on the part of the writer; no warranty is offered for any information contained in this review. Verify all information before attempting any air conditioning repair or maintenance.

As a review, here is a breakdown by model:


CCOT systems (GM-type)

240 1991-1993 ONLY
740 1988- (unable to verify, should be all 740 models)
760 1988- (unable to verify, should be all 760 models)
940 all
960 all
S90 all
V90 all


TXV systems

240 1983-1990 (beginning year unknown)

--
Chris Herbst, near Chicago.

Chris, great AC info.

I would like to send you a web address about an automotive subject I read a few years ago - would like to know your opinion. I read it and copied it years ago and have been using a particular engine product (my choice based on this study).

Would you email me and send me your email address or someones email address you can access, if you want to keep your address private.

diyer

Chris,

Good work here, probably worth noting that 940's and some 740's do not have a high side port to check pressures.

Typically in stock form, all the R12 systems have high side ports, and most (possibly all) the R134a systems do not have a high side port to check pressures. Of course, when converted for one reason or another, often the compressors are changed for 134 compressors (no pressure ports).
--
Chris Herbst, near Chicago.

Bought car in March--127,000--many signs of neglect. A/C evacuated, charged, leak -tested (sniffer) on 6/24. Been fine since (42F lowest at road speed, digital reading at center vent). 8" puddle under condenser this AM.
Relevent work history:

> In May, I replaced small hard line out of condenser "manifold" (?) block. PO had tried to fix w/compression union. No joint leaks when charged 6/24.

> A/C servicing details: 1.96# R134A, 1.5 oz. PAG. "System pressures high." (Ambient about 80F, don't remember what actual pressures he said). Cold air & no sign of leak since serviced 6/24. Till now.

> I replaced radiator yesterday, road tested & ran A/C. No coolant leaks nor (obvious) A/C leaks till this AM

> Flushed leak area w/brake cleaner and ran A/C. Leak appears to be from just above Manifold Block with 3 sensors.

> Line I installed attaches at end of MB. No thread or fitting leaks at this point.

My guess is that with "high" system pressures, 10 years, and now 128,600 miles, it's time had come. I was careful to counter-hold the MB with crescent when I put the small line on. And don't believe I got near the leak spot when putting radiator in yesterday.

Service guy (local, rural, good rep) said high pressure might be due to "clogs" in system. What would be safe pressures at 80F? Any other thoughts?

--
Bruce Young, 940-NA, many 240s (one V8), '73 142, '71 144 (ex circle track car in CT), '67 144 (new), used 122 from '63 to '67

At 80 degrees it should be around 230 high side. Rough figure. The low side will vary with cabin conditions, but when very cold, should run down to the low 20s.
--
Chris Herbst, near Chicago.

Very nice Chris. This one definately belongs in the FAQ's.
--
-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel

Thanks so much!

One important (but for some people unnecessary) point to add is that we do not charge from the port at the receiver-dryer on pre '91 240 models... since as Chris said it is high side. I guess this can be used to monitor high side pressure.

This is an easy mistake for someone who is not sure about the TXV type system... since the suction port is hidden at the back of the compressor.

That's all for my unexperienced opinion (but successfully repaired/retrofitted/recharged TXV system). BTW following my last post, it cycles fine now. I guess being in the garage and not having insulated the expansion valve area i nthe cabin never allowed it to disengage the compressor clutch. I actually really like the user's ability to control the cycling and hence temperature with this system!

Thanks to Chris and to this brickboard in general for al lthe help and advice.

Greg
Montreal - Ottawa
Canada
greg_mustang@hotmail.com

That is very true -- the TXV systems should never be charged by the valve on the receiver-dryer, which would be a mess.

Hopefully this information will help some people out, since A/C work is not that hard once some things are defined.
--
Chris Herbst, near Chicago.