AC high pressure side practically zero

[Flat Six]

Originally Posted by lsf911

When I turn the AC on the high side drops while the low side remains constant.

If gauges connected properly this is impossible unless compressor is running backwards and is now a vacuum pump rather than a compression pump. [Also might be possible w/faulty pressure cut-out switch, I suppose.] Please re-consider the advice rick-I, wwest, and T77911S have offered you.

It's quite possible that the PO screwed up the r134a 'conversion' by mounting the r134a high-side adapter on the compressor low-side Schraeder valve and vice-versa. You might be hooking up the AC manifold/gauges to the 'proper' connectors but the adapters themselves may be installed bass-ackwards.

Please post a couple of pictures of your manifold gauge connected to your adapters/fittings; that will help immensely. Some other advice here will apply at some later point, but all is useless unless and until you get basic and reliable pressure readings first.

HTH

[lsf911]

Scott, Yes that's the highest reading on the high side. I did see the needle move one bar using the high side gauge but it makes sense it wasn't accurate at that low pressure.

Unfortunately I have used the compressor to pump in some air during the hot months. I hope I didn't damage that as well. I will not use it again until I charge the system as well as use dye to figure out what happened to the refrigerant.

Thanks for the response.

[lsf911]

Flat Six,

I hooked the gauges up again and took some pictures. Reading a bit lower but same basic idea.

System Off:



System On:



HookUp:




Pic of Car (just because that is what everyone does)

[GH85Carrera]

It looks like a big H on the compressor with the blue line on it. That is not the way it should be.

[lsf911]

Big H? The low side connector is definitely smaller than the high side.

Not sure what you mean?

[lsf911]

Oh I see it! You mean on the compressor housing, the "H" next to the low side connection. I will go look at that now.

[GH85Carrera]

I suspect that H stands for High.

I suspect the previous owner hooked up the ports backwards. The other members more familiar with that compressor can confirm that. I foresee a refrigerant recovery, port swap and vacuum & recharge in your future.

[bazar01]

It looks like the R134A conversion fittings were switched.

The blue upper fitting goes to the decklid condenser coil which makes me believe that could be the compressor discharge line.

The red lower fitting came from someplace and the tubing looks a little bigger which makes me believe it is the low side suction line to the compressor.

Something is not right.

[lsf911]

No, the "H" is not for High Side. The connection on the housing of the compressor for the high side is larger than the low side.

The low side connection goes directly to the rear condenser. The high side goes forward into engine compartment.

I am thinking it is hooked up correctly and back to the empty system with a leak.

[lsf911]

Okay, does anyone have some pictures of a properly configured Sanden R134a compressor?

[bazar01]

Originally Posted by lsf911

No, the "H" is not for High Side. The connection on the housing of the compressor for the high side is larger than the low side.

The low side connection goes directly to the rear condenser. The high side goes forward into engine compartment.

I am thinking it is hooked up correctly and back to the empty system with a leak.

The high side which uses a smaller refrigerant tubing should go straight to the rear condenser where superheated refrigerant gas is condensed into liquid.
While the low side with a bigger refrigerant tubing should come from the front evaporator where cool refrigerant vapor is sucked from.

[Flat Six]

Originally Posted by bazar01

The high side which uses a smaller refrigerant tubing should go straight to the rear condenser where superheated refrigerant gas is condensed into liquid.
While the low side with a bigger refrigerant tubing should come from the front evaporator where cool refrigerant vapor is sucked from.

Exactly. As suspected, looks switched. BTW, I wouldn't do any more work until you replace all hoses that don't have proper fittings -- hose clamps are okay for low-pressure water cooling but not on an AC system. At best you're inviting leaks. At worst, well . . . you'll quickly see what 235+ psi on the high side will do. PO's 'conversion' looks pretty butchered to me; I'd do an end-to-end inspection.

Thanks for the extra picture; nice car.

[wwest]

That "blue" capped line that goes to the rear lid condensor is the HIGH side!

My '92 LS400 uses hose clamps, OEM, and has had no problem.

[Flat Six]

Originally Posted by wwest

My '92 LS400 uses hose clamps, OEM, and has had no problem.

Not gonna second guess ToyotaMoCo for its OEM design, but if the OP's ports aren't designed that way (sufficient wall thickness to deal w/additional clamping pressure + retention flare so clamped section won't slide off) IMHO it'd be somewhere between silly and stupid to move forward with those clamped hoses. Given what we already see about the [ahem] 'care' that PO used for this 'conversion' I'd be especially suspicious about the rest of the system. Opinions differ, YMMV, etc.

[T77911S]

Originally Posted by Flat Six

Exactly. As suspected, looks switched. BTW, I wouldn't do any more work until you replace all hoses that don't have proper fittings -- hose clamps are okay for low-pressure water cooling but not on an AC system. At best you're inviting leaks. At worst, well . . . you'll quickly see what 235+ psi on the high side will do. PO's 'conversion' looks pretty butchered to me; I'd do an end-to-end inspection.

Thanks for the extra picture; nice car.

not a good clamp. go to an AC shop. they can make a crimped hose. i made some for my 280z when i worked at an auto electric shop. the 911 AC can see higher pressures than normal, upwards 300, maybe more.

[kuehl]

Your low and high side R134a 90 degree hose fittings are swapped: reversed:
A High side (RED colored cap) 90 degree , smaller diameter hose, larger diameter R134a service port, should be on the upper port of the compressor marked with the "H" (for high) on the mounting ear adjacent to it; this would be the hose between the compressor outlet port (H) and the deck lid condenser inlet.
B) Low side (Blue colored cap) 90 degree , larger diameter hose, smaller diameter R134a service port, should be on the lower port of the compressor marked with the "L" (for low on the mounting ear adjacent to it; this would be the hose between the evaporator outlet (in front trunk's smuggler's box) and the compressor inlet.

"The other day I purchased an AC manifold gauge set. Today I hooked it up for pressure readings. With the car running at about 1800 rpm's and the AC setting on high I get 35lbs on the low side and just about zero on the high side. The high side pressure does go up to about 10 lbs when I shut the system off."
So if you swapped the service hose connections at the service gauge, so that the blue hose was connected to the red gauge and the red hose connected to the blue gauge what you would be reading would actually be... high side 35 and low side 10. Which typically means you are very low on refrigerant. Since you do not have a low-high pressure switch this means you compressor will turn and pump but you don't have enough refrigerant in the system to carry enough oil to keep the compressor lubricated when its running.... so DO NOT run the compressor any longer. Disconnect the wire plug running to the compressor.

1) Have what ever refrigerant is in the system removed.
2) Inspect the receiver drier; If its a factory Behr system the drier is usually located in the the LH front fender on the wall on the back side of the tire. If another brand system such as a VPC it would be in the RH front fender. You should have a new new drier, if no get a new drier.
3) It looks like you are using the original hoses. If they are not barrier hoses you will be recharging this system often; how often depending upon how often you use it, the system pressures and outside temps, and condition of the hoses.
If you plan on keeping this car get a complete set of barrier hoses. As a minimum if you want to 'play' with what you have, at least take of the hose assembly between the compressor outlet and the deck lid condenser and have a 90 degree fitting with the Red R134a service port crimped to your hose with a ferrule. On the larger diameter hose connecting to the 90 degree fitting with the Blue low side service port you could use a hose clamp but a crimped fitting is preferred.
If any of your hose connections use o-rings replace them (looks like your compressor is flare fitting based on the shape of the nuts).
4) You don't have a low-high pressure switch to help protect the system, you should get one.
5) Since the R134a conversion that was previously done was questionable, you got to wonder if they put in the correct type of refrigerant oil and how much.
If you want to do the job 'right and once' you might as well remove the compressor, dump out what ever oil is in it, liquid flush the front and rear condenser, remove the evaporator, take off the TEV and liquid flush the evaporator.
6)... if you really want to know what road you should go down the read
The Mr. Ice Project
as primer to understand the basics. And there are plenty of good threads here on upgrades and DIY through out Pelican.

PM if you need more help.

Griff

[GH85Carrera]

There is your answer, from a real expert.

AC work is pretty easy, one you KNOW the basics. Read the Mr. Ice project link above. And read the various threads on the board. That is a LOT of reading and research. If you like to learn you will learn a lot. I enjoyed my education with AC systems.

[wwest]

One more point. If you install the "binary" pressure switch as Kuehl recommends it will both:

1.) Protect the compressor from eventual failure due to lack of sufficient refrigerant in the system.

2.) Prevent the compressor from from over-pressurizing the system when the evaporator load is such that it cannot reach the thermostatic setpoint. That might very well also reduce the refrigerant leakage rate to something more common, equal, to the use of these same hoses industry wide.

[lsf911]

Thanks a lot guys. Very helpful stuff.

Griff, thanks for the offer. I may be in touch when I dig into the AC system.