AC high pressure side practically zero
 

I apologize if this had been covered in previous threads but I couldn't find anything describing my AC problem.

I have an 83 SC that has an R134a conversion kit that was installed by a PO. I have owned the car for about a year and since my ownership the AC has not worked. It blows hot air, temperature depends on outside air temp. It is definitely not blowing cold air.

The compressor appears to work, I can see the clutch engage and disengage depending on settings. All AC equipment appears (by visual inspection) to be in order. At least all the components are mounted in the car and blowers all work.

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.

To me it sounds like a clogged system, but where do I start? Any suggestions on where to start looking (i.e., Expansion valve, Evaporator, etc)?

Thanks for your help!

I imagine that your low pressure problem is caused by little to no refrigerant in the system . . .

Your system is mt. When you shut the car down both hi and low side equalize if you don't know what you are doing have it charged at a shop and have them check for a leak Freon does not just go away
Should you attempt safety glasses are a must
Ernie 81 sc

Ronnie, its the high side that has a bad reading. I think 35 lbs on the low side isn't too bad.

emac, if there was a leak, wouldn't all the refrigerant leak out in a years time? There wouldn't be 35 lbs on the low side.

I hate to throw thousands away on an AC repair when I can do most of it myself at a much less expense. I just don't want to start replacing everything. I am sure these readings must point to something in the system. A starting point.

Why would the pressure read almost zero on the high side and at the bottom of the good range on the low side?

Are you sure the gauge was seated all the way and the adapter was screwed all the way on?

There is no pressure cutout on my 88

Yes, it was seated all the down and screwed down to open the valve. I did get a low reading until I turned on the AC. At that point it went to zero.

Do you have the two readings reversed? Like the high side reads 35 and the low side 0?

That's a good thought, but no.

I have a Harbor Freight AC manifold gauge set with red and blue lines. Also with the R134a conversion kit I can't hook them up wrong.

The readings are weird, I will try again.

lsf911
You stated that you had the car for a year and the A/C never worked, so you don't really know how long the system has been low on Freon. I have seen a system that had a rock pierce the condenser and needless to say the freon lasted seconds, on the other hand a very slow leak could in fact take a year. As I stated in my post once the system is off both sides balance out so if you are getting around 10 lbs on the high side I would guess you have about 15 on the low. They sell dye that could be introduced into the system and this would be a starting point for finding the leak. As you stated everything appears to be normal. The bottom line is with the readings you have you will not cool, I stand by a nearly M/T system

Thanks Ernie. That does make sense to me. I will try the dye.

You will put the dye into the suction side (low) side.
Im sure you will find the issue.

Assuming you are not turning the thermostat down when the compressor cycles off it does that normally only when the evaporator has been chilled in accordance with the setting.

~70 PSI for both high and low is the approximate norm with the system off and having time to equalize. 35 PSI is the approximate norm for the low side with the compressor functioning or having just cycled off.

I would mistrust the guages.

PO installed a pressure switch?

Low charge and the compressor functioning, pumping the low side should ALWAYS be lower than the high side....wrong color caps on the fittings....it happens.

you still have schreader valves?

i have had the part in the hose that pushes the valve down go bad. i bought a bag of rubber seals and the center part at the parts store.

if not, you have the hoses connected wrong. i cant think of any way you could have 35psi on the low side and 0psi on the hi side. unless something in the compressor could do it, but then i still have my doubts.

does the compressor have the service valves that you can close the ports?

Do a search on Jim Simms and AC. Do you have a 134a receiver/drier? The adsorbent on a R12 isn't compatable and will foul and block the system, same with the oil in the system and the expansion valve. I'm no expert but you can't just change the refrigerant. BTW, I'm no expert, my weak A/C temps tell me that.

Sense you have gages. You aught to drain the refrigerant in it and refill with the correct amount of refrigerant or somewhere close and start from there. Then you might have good a idea of what is working correctly and what is not. Is the compressor clutch cycling allot or is it running all of the time.

AC system check is a series of process checks.
Pull a vacuum on the system and you will find out if it will or will not achieve vacuum watching your gauge manifold while the pump is running. If vacuum is not achieved, you have a big leak.
If vacuum is achieved. shut off the gauges and turn off the vacuum pump and watch for a few hours for any pressure increase. Loss of vacuum and pressure increase is indicative of a leakage.
If still inconclusive, pressurize system with nitrogen to 150 psi and watch for loss of pressure over a few hours.
If it checks out leak tight, then you can start checking compressor operation by putting a refrigerant charge and watching low and high side pressures. If high side pressure is still zero or low, compressor discharge valve is suspect. Replace compressor.
Once compressor is replaced, you may find your AC is working but may also find it does not have enough cooling capacity and the frustration sets in and you start thinking about upgrades.

Step one is to look at the pressure in the system.

If you get an impossible reading it is time to evaluate.

Okay, thanks to all who responded.

I performed the pressure readings again. I think the high side gauge is not functioning properly out of the box.

I used the low side gauge and took measurements on both low and high with the results being 35 lbs on each side with the system off. When I turn the AC on the high side drops while the low side remains constant.

To answer a couple of questions from replies, I did use the thermostat to cycle the compressor on and off. It's cold here now (well not today) so the garage has been around 50 degrees. When I turned the thermostat from low to high the compressor kicks on and off.

I do not know if the PO replaced the receiver/dryer to an R134a. The only thing I know for sure that he replaced is the compressor and fittings for R134a.

I am thinking what Ernie said is true. Low refrigerant with a leak somewhere...possible other things too.

35lbs is your highest reading on the "high side" then it drops from there when you turn the compressor on? I'm asking because that would be so low that it would likely not register on a high side gauge.

I would also add that if your high side pressure is 35lbs max then you need to stop using the compressor until you can get a proper charge run in.

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

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.

Flat Six,

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

System Off:

http://forums.pelicanparts.com/uploa...1352747807.jpg

System On:

http://forums.pelicanparts.com/uploa...1352748232.jpg

HookUp:

http://forums.pelicanparts.com/uploa...1352747922.jpg
http://forums.pelicanparts.com/uploa...1352747982.jpg

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

http://forums.pelicanparts.com/uploa...1352748070.jpg

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

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

Not sure what you mean?

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.

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.

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.

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.

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

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.

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.

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.

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.

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

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.

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.

Thanks a lot guys. Very helpful stuff.

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