j.kenzie@sbcglobal.net

It's missing. It is a flimsy black plastic sheet which goes forward about 10" from the base of windshield end of your engine compartment to the ridge behind your air intake. It seems to me if your recirc flap is working, then you won't be drawing air from this area anyway. The part can be ordered, seems like $80?

j.kenzie@sbcglobal.net

Hi Rich,
I look at these problems as follows:
Your HVAC system has two parts. Refrigeration/heating system, and control/distribution system.
You may have problems in either or both parts. Does your evaporator or nearby pipes get cold? does your condenser get hot? Can you get someone to put a set of gauges on your car. It may just need a good evacuation and proper recharge with leak check.
In the control part of the system, a bad heater valve, even a new one can be bad, is a common failure point. You could put a padded clamp on your heater hose to rule this out. If you have a bad temp sensor loop, the A/C may only work in lowest temp setting. I had this happen.
The more you narrow this down the closer you'll get.
Good luck,

RichS 1986928

I have the plastic piece, just removed for the picture.

Yes, the pipes going into the car are cold.

Heater valve is brand new and I watched it close.

I think this hissing must be from the evaporator or close to it.. behind the dash in a nicely
impossible place to get to.

i guess I'll need to have it checked for leaks.

j.kenzie@sbcglobal.net

If the heater valve is really closed, and the recirc flap is really closed, and the evaporator is really cold, you should have cold air coming out somewhere. You could have a partially blocked expansion valve that decreases your cooling capacity and leaks down audibly on shutdown. Some R134 conversions don't address changing the expansion valve or the receiver/dryer. I don't know, obviously, but could be a clue. A/C gauges should tell you if this applies.

RichS 1986928

I guess I'll have to go somewhere that A/C gauges. I already dropped $300 on the first trip
to an AC shop.. That was recommened... Great cold air, that drained out on the driveway
as soon as I got home from a leaky compressor. That is why I want to know as much as
possible before I take it to a shop. That was the worst $300 I ever spent.

It would not surprise me if the R134A "conversion" that was done consisted of draining the system
and filling it with R134A and nothing more. I replaced the dryer.. where is the expansion valve
and how do i check to see if it's right for 134A?

thanks

j.kenzie@sbcglobal.net

You can just see it to the right of the orange wire in your underhood picture. You can buy new since if defective indicated by overpressures or other conditions I don't think they are repairable. $300 for evac/recharge seems excessive, you may need another shop. There are numerous articles on a/c here on rennlist.

RichS 1986928

Yeah, I'll have to see if anyone in the Denver area can recommend a good shop.

anybody happen to be reading this post that can?

dr bob

Rich--

The expansion valve doesn't know when the compressor turns on or off. It only responds to changes in pressure, and adjusts to keep the suction pressure correct for the temperature it measures in the return line. So when you have the system pressurized (compressor running for a bit) it starts to work, and continues to work until all the pressure from the high side bleeds into the low side and finally the two sides of the system are at equal pressures.

The expansion valve will hiss some when it's working. It's normal, as it has liquid coming in one side, and the liquid boils as it absorbs the heat in the evaporator. The liquid expands and cools the evaporator, which is gathering heat from the air passing across its surface. That boiling action can be a little noisy, but isn't something you'd normally notice with the fans running. In the meanwhile, the gas returning from the evaporator is warmed some by the heat from the evaporator, but will still be a lot cooler than ambient if you are feeling for cold in the lines.

ew928

Can't remember what this doohickey is called nor if it had been checked. (Freeze switch?)
I do remember I had a bad one and had to swap new one in and adjust the screw till I got about 35 deg at the center vent.

RichS 1986928

OK, just heard from the shop, their 'sniffer' found a leak at the low pressure switch.

Is this the switch they are talking about? Does this swtich need to be special for a 134A conversion?

And how hard is this switch to change myself? Or should this be done
by someone with AC equipment. They quoted me $207 for parts and labor
to finish the job.

BTW, this is just a standard ASC mom&dad shop, nothing fancy

w3lfd

Low pressure switch typically is the switch at the receiver / dryer located near the front passenger side (ahead of the radiator etc.). At least, that is where it is on my 1982. Definitely not 41.

Number 27 on pgs 435/436 of this file: https://techinfo.porsche.com/techinf...86_KATALOG.pdf Illustration 813-25

RichS 1986928

Thanks,

Another question: Is it possible for this switch to actually leak or is it much more
likely that all I need is the Oring?

Is this pressure switch different for R134A vs. R12?

w3lfd

I doubt that there is a difference in the switch based on refrigerant type. Also, probably leaking due to a poor sealing than anything else.

dr bob

On the S4, the switch is the lower of the two devices on that little tubing manifold. Since you have done the R-134a conversion, you'll want to convert to the later GTS switch that combines both under- and over-pressure protection. The switch screws on over a schraeder style valve in the port, so you can change the switch without sacrificing your refrigerant charge. This is easily in the realm of DIY. The switch has an o-ring seal where it joins the port. The original o-ring should have been upgraded when the conversion wwas done, since the original o-rings don't seem to get along well with the synthetic lubes used with R-134a. Maybe it was missed.

Switch is a common part, although you might want to get just the right one from one of our dedicated suppliers. A phone call or visit to Jim at 928 Int'l is my favorite way to get parts for my toy.

WallyP

A couple of comments:

The hissing, as Dr bob says, is probably the normal operation of the expansion valve. Some are noiser than others, but a hiss is not too unusual. Your description is spot on for the valve hiss.

With the A/C operating, feel the return line - if it is cold all of the way to the compressor, the refrigeration system is probably working fine.

A shop's freon sniffer can find a one-ounce per year leak - may not be worth fixing, especially on the R-134a system. (Not politically correct...)

If the refrigeration system is working, the next check is the temp control flap. Look on the driver's side of the HVAC box and find the black servo box. With the system running, slowly move the temp lever from full cold to full hot and back while watching the top of the servo. You should be able to see the temp control servo move up and down. If nothing moves, you now know where to start looking.

The seal in the engine compartment is the rubber seal lying on top of your engine in your photo. If it is not in place, very hot air from the engine compartment flows directly into the HVAC air inlet.

If you will send me an regular email with a request (techAT928gt.com - change AT to @) I will send you a paper describing the HVAC system.