When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
.
2. Not all expansion valves are the same. Your picture tells us you have a Behr packaged item made by Egelhof- was that offered as a confirmed 928 spec part or is it something that fits but not necessarily the 100% correct item? We have had recent examples where expansion valves were supposedly for the 928 but under performed and then the same system worked well when a part supplied by one of our recognised parts gurus was installed.
.
+1 to what fred said. I struggled to get my AC to work properly and the missing link was the proper expansion valve. installing an incorrectly calibrated valve from a known supplier would not allow dash temps to get below 50' during the best conditions. installing a made in France, Egelhof made all the difference: my AC is ice cold under ALL circumstances
AC expansion, the old (original) valve had a plastic cap on one end with some insulating material
It was a 'protective' cap. The insulation was 'packing'. Sometimes, when the TEV leaks at that end you will find residual refrigerant oil under the cap. Both, are not needed.
I repeat, the cap holds insulation to minimize undesired thermal influence. Any one who understands how a TXV and A/C in general operates can appreciate this. The T in TXV stand for thermal, hence it adjusts based on temperature.
The caps with fiberglass insulation or some other form of insulation are often found in vehicle where the TXV is in a warm place.
I usually see them when the TXV is in the engine compartment. Most manufactures have moved these block style TXV's into the passenger compartment and obviated the need for insulation.
In the A/C service industry the TXV valve can be tested by spraying the "Sensing disc" with a can-of-air upside down to freeze it and then observe the metering oraface. As it warms up, movement can be observed.
Here is how Toyota does it on cars where the TXV is in a warm/hot place.
I repeat, the cap holds insulation to minimize undesired thermal influence
You may have a point there on the early 928 as my 78 had the cap with 'insulation'. However, when I converted it to R134a with a new valve I did not put back on the cap and the system blew ice at 95F without any problems. As well, so did my 1984 928 and my 1989 928, but I don't recall any caps of the 89.
I sense what the 'cap' was for insulation in the particular design having maybe a hose next to it that was giving off heat (can't tell ya cause I sold it years ago), but you can see below in the pic where that might be helpful. Otherwise, most TEV's do not require insulation .
I repeat, the cap holds insulation to minimize undesired thermal influence. Any one who understands how a TXV and A/C in general operates can appreciate this. The T in TXV stand for thermal, hence it adjusts based on temperature.
The caps with fiberglass insulation or some other form of insulation are often found in vehicle where the TXV is in a warm place.
I usually see them when the TXV is in the engine compartment. Most manufactures have moved these block style TXV's into the passenger compartment and obviated the need for insulation.
In the A/C service industry the TXV valve can be tested by spraying the "Sensing disc" with a can-of-air upside down to freeze it and then observe the metering oraface. As it warms up, movement can be observed.
Here is how Toyota does it on cars where the TXV is in a warm/hot place.
I have no problem with you having a different opinion about how something works but when you make a statement to the effect of "how anyone who knows how these things works can appreciate this" I offer some "tongue in cheek" insights that might just change the way you view this matter.
1. The "T' in TXV stands for thermostatic [not thermal]- I suspect you well understand this but others may not. The TXV thus targets a specific temperature that it tries to maintain. A better description of its functionality would be "a self regulating temperature control valve". The TXV the 928 deploys has a sensor bulb in the gas outlet port that as I understand is referenced to the outboard side of the diaphragm via the capillary tube. The closed circuit contains R134 and the system is calibrated to flash off the liquid and generate more pressure in the circuit thus changing the force balance across the diaphragm. Thus excessive temperature change could adversely impact operation and that part is quite correct- the key part here is "excessive" and what is understood by that. As best I can understand the only difference between a TXV designed for R12 and R134 is the type of refrigerant used in that sub system.
2. The TXV is designed specifically to keep a fixed amount of superheat in the refrigerant. No idea if you know what superheat is and why it is important but it acts as a safety feature to prevent liquid forming whilst passing through the hose to the compressor and thus stuffing up the compressor. with hydraulic lock.
3. This is a 928 forum and obviously one presumes you understand that. Doubtless the case you mentioned in a Toyota may well have relevance to the model it was fitted but on a 928 it is totally irrelevant. If a TXV is fitted directly in the engine bay then it may well make sense to insulate the diaphragm assembly. However in the case of the 928 the TXV is fitted behind the firewall. Amongst other things the blower and the fresh air intake are situated there. If you understand the cars aerodynamics you would know there is a high pressure front formed at the based of the windshield and the firewall has a rubber seal on its top edge to prevent heat from the engine bay getting into that chamber. In short the air in that area is going to be at ambient temperature or very close to it- presumably not at all like the case you mentioned.
4. Not particularly relevant but perhaps falsely associated as a reason for need of insulation - the TXV test you mentioned is standard fair but it is not carried out using a can of air - it is a can of something that in years gone by would likely have been R12 [when used as a propellant]. The can is inverted so that it directly sprays liquid onto the metal surface where it flash vaporises at quite a low temp and thus gives the opportunity to see the needle moving. So yes ambient temps can influence performance but not in this particular case where air temps are going to be in relatively narrow band- the designers would know this and take it into consideration.
Not specifically relevant but it pisses me somewhat that the environmentalists got R12 banned when most of the fugitive emissions came from bloody hairsprays and the like - not car a/cs- kind of ironic that our local Gov banned R12 some years ago and enforce it yet you chaps whose EPA came up with such can still get it in the States- urrgh!
5. Oraface [horror face] might well describe your NSA secretary [Bolton] but for completeness we are talking about a metering "orifice" and a variable one at that.
If the expansion valve needed insulation it would be provided in the box and mentioned in the WSM. There is nothing in the box and nothing in the WSM about it either.
Fred's description is closer to my understanding of the TXV functions. The end of the cap tube in the valve body is closer to the vapor flow from the evaporator, so less sensitive to exterior temperature.
FWIW, these valves are so cheap that it's hardly worth "testing" them unless you are trying to confirm that a malfunctioning TXV was causing the symptoms you are trying to eliminate. Once you have one out you are going to replace it anyway.
My somewhat unmolested 1986 has the cap. No shock its for thermal management since it's close to that pipe. There's a lot of minutiae not covered in the PET or service manual.
My somewhat unmolested 1986 has the cap. No shock its for thermal management since it's close to that pipe. There's a lot of minutiae not covered in the PET or service manual.
The notion that the a/c system and the heater system need to run at the same time sounds somewhat strange to me.
I would hope the temperature control system would shut off the a/c before it introduces heat but I dare say stranger things have happened.
08-06-2019, 06:26 PM
