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Anyone Know About Car A/c Systems?


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Concerning a 1995 Toyota Paseo 2D Coupe

I tried to charge the damn A/C...I must be stupid because I followed the instructions exactly, and it does not seem to be working. Here is what I have done, and what happened.

I was told by the instructions to start the car and run the A/C at full throttle, and be sure the compressor clutch is engaged. I did this and confirmed the clutch was engaged by noticing the drop in RPM and increase in load on the engine. Next I was supposed to connect the pressure guage to the low pressure side of the A/C system and check the pressure. The pressure was between 18-23 PSI. Which was low as I suspected. The instructions stated that with an ambient air temperature of 95 degrees the low side pressure should be between 45-50 psi.

So I started to charge the system as the instructions stated. I connected a r-134a canister the other end of the guage and used the valve to crack open the can and begin delivering refridgerant to the low side. I could hear gas moving out of the can into the low side, and could feel the can getting cool. So I am sure the gas was leaving the can and entering the Low side.

This is when things went bad....while I was in the process of recharging the compressor clutch disengaged as sometimes happens when the A/C does not need to run all the time. When this happened the low side pressure suddenly increased to 100+ psi. I knew this was very wrong so I panicked and thought the damn low side would explode. What happened next was even stranger. The compressor clutch re-engaged and then the pressure suddenly dropped back down to a safe level around 20 psi. So I continued adding gas. I added a full can and a half and could not notice any difference in pressure while the conmpressor clutch is engaged...this does not seem right.

Finally I have been told the low side pressure should stay pretty much the same regardless if the clutch is engaged or not. What I am hoping is that someone here can tell me if my A/C system is screwed or if I am not recharging correctly, or if it might be my guage is screwed up. Thanks for any help.

Other info:

I know for sure it uses r134a...there was a little sticker right next to the low and high pressure ports saying so. I am about 99% sure the can was screwed on tight enough...I was actually a little worried I screwed it on too tight. I was not aware of the window on some cars to "see" the fluid...I will try that tonight. What really concerned me was the low side pressure sky-rocketing when the clutch dis-engaged...I hope I did not just totally ruin the A/C system....Since my car is a 95 and we expect to sell it this winter, I do not want to take it in and pay 100 bucks just to find out it will cost even more to fix.

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I know I can take it to a shop and get it looked at, I am trying to avoid the cost associated with that, and fix it myself...I am thinking the compressor could be bad, which might explain high pressure gas in the low pressure side when the clutch disengages. If I had a leak all the gas would leak out, and there could never be over pressure building. The other possibilty I thought of was maybe there is a blockage in the high pressure side of the system forcing high pressure gas into the low side when the compressor cluctch disengages. Am I missing something?

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does it work now? If so then no problems. The pressures will equalize when the comprossor is'nt on so don't worry about that.

the deal is that you've got a slow leak and that should be found before you recharge it. And to recharge it properly it needs to be vacuumed to about -30 inches, held for a bit to make sure no leaks, then refilled to the proper amount.

it's nice to have the guages, but the rest of the propper tools is what you need to do the job right.

The whole job should cost less than 100$. good luck

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Thanks for the good information...I will take it to a friends house who is a bit better of a machanic than I....I think I know everything that needs to be done now.

I think there may be a slow leak. I was hoping I could just make the thing limp through september, without have to pay the big money to fix it good.

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OK....I did some more troubleshooting... here is what I did tonight and what I experienced.

I started the car and turned the A/C on full with recirculate. I place a digital thermometer in one of the vents. I opened the hood and attached the pressure guage to the low side fitting. And to my surprise the pressure guage showed approx. 33 psi. This is with an ambient air temperature of around 75 degrees. According to the manual I should have between 35-40 psi with that ambient temp. I located the site glass on the high side line just in front the A/C radiator fins. The liquid looked clear and I could see no bubbles. So everything is looking pretty good, and I go back to the driver's seat and begin watching the vent temperature drop to about 64 degrees. At this point the vent temp would go no lower, so I began raising the RPM's to typical highway speeds. This is where things got weird.

After revving the engined to about 2000 rpms for about 2 minutes, I notice the vent temp is rising instead of dropping. At this point I check the pressure guage on the low side and discover the pressure has dropped from 33 psi before to well under 15 psi. I looked at the site glass and the liquid was still clear, but you could tell the liquid was only filling halfway up the high side line.

I performed this procedure twice, and got exactly the same results. The good news is that this time the compressor clutch stayed engaged the entire time the A/C was on. This may have something to do with the fact that the ambient air temp was much lower this time.

I also checked the low side pressure when the A/C was not on, and determined it to be approx 130 psi.

I verified the A/C radiator fins were clean. They were not spotless mind you, but they were fairly clean and straight. I also could not see any bent or dinged lines.

Any more ideas, anyone? I think it is time to succumb to the repair shop....in the middle of August, the shops around me are charging out the @ss. :(

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I think she's still low on refrigerant. could also be a restriction on the low side or a faulty metering device. My bet is still low.

Needed more info, what were your high side readings(engaged and disengaged and idle/2krpm)? kudos to you for actually putting in the effort. I'm ripping through my 1300 plus text book trying to help.

Good luck.

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