A/C pressures in a 94 Lexus ES300

[82DMC12]

Hi Group,

I have had A/C trouble on a 1994 Lexus ES300 for a couple of years now. I recently bought an A/C manifold gauge set so I could try fixing it, if I can. It uses R134a.

I see the static pressure with the car shut off is 66 PSI on the low side and 81 PSI on the high side. This gauge set has three bands on the outside of the dial that that show different scales for different refrigerants. The main gauge, on the low side, says 66 PSI, then the needle is also pointing to "+20" on the outer R134a scale. Does that mean the pressure is actually 86 PSI? The high side points to 81 PSI "+24".

When I turn the car on, and turn the A/C to max cool, the compressor turns on but never shuts off. The needles on gauge do not change either. They are still in the same spot as the static position.

What does this indicate? The factory specs show Low side at 22-36PSI, while the high side should be 198-227 PSI.

Is my system under-charged? Over-charged (I did add a lot of freon last year when it stopped working but I didn't have guages then. I used those cans with the dials on the them and filled until the can said it was "OK")? The troubleshooting tree in my factory book says a high low presure and a low high pressure means the compressor is defective. Anyone out there agree with that?

Thanks for the help -

Andy

 

[Quest]

OK, w/o going further into confusion. Just based on your description of symptoms (compressor turns on but never shuts off or even cycles) On the flip side: if your compressor cycles too frequently than expected, that's an indication of too low of refrigerant charge.

Knowing that R134a system is very "finicky" to deal with and would require very precise amount of oil, refrigerant, etc. you shall STOP right now and go find a reputable A/C shop to service your system for you.

Like I said in the past postings: R134a is not meant for weekend DIYers as far as refrigerant recharging's concerned.

 

[Chris142]

If the readings don't change or change very little when the compressor is on either the compressor has no compression or the expansion valve is stuck.

 

[82DMC12]

Hi Chris,

I replaced the expansion valve already, probably two years ago. I heard they were one of the few problematic parts of these cars. I had the system then recharged by a shop who put the system under vaccum for over an hour, and they said it was tight as a drum, so I am pretty sure it was installed properly.

I understand what Quest is saying, but I just want to get a handle on what the problem is before I go in to the shop again. These guys charge about $120 just to touch the A/C. If I can do my own diagnostics and pin point the trouble, it will be a lot easier on the wallet. I can put the compressor in myself, too, if I need one.

Andy

 

[Quest]

Chris is right about the fact that if the expansion valve is stuck, you may get static readings on both sides regardless of whether your compressor is running or not.

since you've only posted static readings on both the low side and the high side (e.g. low is @66psi?) once you fire up your car and let the compressor kicks in, it may drop as much as 10psi and then cycles between the 2 readings you have on the low side if everything is normal.

Yes, I know A/C service is expensive but there is no way a weekend DIYer can do a proper R134a servicing w/o the proper knowhow, tools, measurements, deep vacuum pump, all sorts of freon leak detection tester, etc. And also another sad fact is that not all PAG oils for R134a are fully compatible to each other (e.g. my Honda calls for Sanken SP-10 that is slightly different to the other synthetic refrigerant oils I normally stock up with (Daikin type or other domestic branded PAG oil) and some vehicle systems are very sensitive to mixing "foreign" oil types.

Also: if your expansion valve is stuck (not likely but possible still), there's still absolutely nothing you can do about it other than to send your vehicle in to an A/C shop, break open the system, drain the oil (evacuate the refrigerant)...before they can get to your expansion valve. And then again: they will have to add back the proper amount of oil based on your vehicle specifications (no guessing game here--has to be precise), deep vacuum your system, add the precise amount of refrigerant, leak test your entire system, etc. before you can drive your vehicle home.

Gone where the days where R12 were readily avail off the shelf of Kmarts and a universal system that is highly tolerable to small DIYer mishaps during weekend refrigerant recharge and so on.

There's only that much you can do RE: servicing on modern R134a systems.

Good luck to you.

Q.

 

[mechtech2]

The high and low side should be the same, in the static rest condition. This may take a while to achieve, if the system was recently used, however.
Your compressor is puked, or the restrictor/orfice is plugged, or both.
The marking on the gauge set are for pressures of different refrigerants at different temps. Home R22 systems, for example, can run at almost twice the pressure of a car's AC.