Air Conditoning problem
05-21-2017, 11:08 AM
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Air Conditoning problem
Hello, I have a 1990 1 Ton 2wd truck with the 3ZVE V-6. My AC compressor will only cycle on for 7 seconds a minute. Inside temp will not got below 65F with OAT mid 70's. I evacuated and charged the system per specs. When I jumped the compressor clutch to "on" my dash vents go to 48F in less than 4 minutes. I have been reading the forum and have removed my glovebox. I am going to check the Thermister first (using the online mantenance manual), the pressure switch second and if they are ok I guess it would have to be the AC Amplilfier? I see the RPM adjustment knob on the amplifier but at this time I will not move it. Has anyone had experience with this model? What would be the most likely part to fail? Are the parts still available? I could not find them on Rockauto. Thank you for the help!
Last edited by Eddy748; 05-21-2017 at 02:10 PM.
05-21-2017, 12:15 PM
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Update: I tested the thermister (wiring harness). My reading was 1.375 on the 2K ohm setting. The specs called for 1500 ohms at 77F and I had 1375 ohms at 85F. (correct?) So with the chart numbers falling with an increase in OAT I would think this was ok. ?
Next I jumped the clutch to run the compressor and checked the pressure switch. I had continuity on the contacts while the AC was running cold for the whole time I checked. (2 min). I did not hook the pressure guages back up but last night I had 40 psi low and 180 high with the compressor running.
I am not sure what could be wrong at this point unless there is a problem with the AC Amplifier. ? Any help would be greatly appreciated. Thank you
I tested the AC Amplifier per toyota service manual. The first check of continuity on the list #7 to #8 I had 2.43 ohms but the chart called for continuity.
The second check was #8 to ground. I had .157 ohms. The chart called for continunity. All other checks were to specs except for the last on the list for resistance between #2 and #5 with thermostat on minimum cool. The chart said 3 kohms. I had .000 ohms. ??
Next I jumped the clutch to run the compressor and checked the pressure switch. I had continuity on the contacts while the AC was running cold for the whole time I checked. (2 min). I did not hook the pressure guages back up but last night I had 40 psi low and 180 high with the compressor running.
I am not sure what could be wrong at this point unless there is a problem with the AC Amplifier. ? Any help would be greatly appreciated. Thank you
I tested the AC Amplifier per toyota service manual. The first check of continuity on the list #7 to #8 I had 2.43 ohms but the chart called for continuity.
The second check was #8 to ground. I had .157 ohms. The chart called for continunity. All other checks were to specs except for the last on the list for resistance between #2 and #5 with thermostat on minimum cool. The chart said 3 kohms. I had .000 ohms. ??
Last edited by Eddy748; 05-21-2017 at 03:43 PM.
05-21-2017, 12:45 PM
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Humm. I am still an A/C novice myself.
What refrigerant are you using? R12? R134A?
Most people recommend charging R134A to about 80% capacity of the R12 specification.
There was a Technical Service Bulletin Toyota put out in 1998 for R12 to R134A conversions showing how much oil and how much refrigerant should be in the system when converting.
Unfortunately the link I have for the page no longer works.
You may already know this though.
Are the condenser and evaporator clean?
Does the cab get colder if you drive around?
Also, Scope103 has a good thread on A/C:
It is good to read if you haven't already: https://www.yotatech.com/forums/f116...-r134a-284801/
What refrigerant are you using? R12? R134A?
Most people recommend charging R134A to about 80% capacity of the R12 specification.
There was a Technical Service Bulletin Toyota put out in 1998 for R12 to R134A conversions showing how much oil and how much refrigerant should be in the system when converting.
Unfortunately the link I have for the page no longer works.
You may already know this though.
Are the condenser and evaporator clean?
Does the cab get colder if you drive around?
Also, Scope103 has a good thread on A/C:
It is good to read if you haven't already: https://www.yotatech.com/forums/f116...-r134a-284801/
Last edited by old87yota; 05-21-2017 at 12:49 PM. Reason: Added Scope's thread link
05-21-2017, 01:16 PM
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Thanks Old87, It is a converted system. It had 134A and I evacuated and recharged with 134A and added ester oil that was in the system to the new drier. I was as 24oz with the reduced amount from R12. It is cooling to 48F if the compressor stays on (jumped), but the issue is the compressor cuts out in only 7 seconds and will not turn back on for 50 seconds. And again cuts out in 7.
05-21-2017, 03:09 PM
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... I tested the AC Amplifier per toyota service manual. The first check of continuity on the list #7 to #8 I had 2.43 ohms but the chart called for continuity.
The second check was #8 to ground. I had .157 ohms. The chart called for continunity. All other checks were to specs except for the last on the list for resistance between #2 and #5 with thermostat on minimum cool. The chart said 3 kohms. I had .000 ohms. ??
The second check was #8 to ground. I had .157 ohms. The chart called for continunity. All other checks were to specs except for the last on the list for resistance between #2 and #5 with thermostat on minimum cool. The chart said 3 kohms. I had .000 ohms. ??
The only thing that I can think of that would produce "on for 7 seconds, off for 50 seconds" is a signal from the pressure switch. But you have already checked that with the compressor clutch forced to close (and the compressor to compress).
05-21-2017, 03:43 PM
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After much toil I turned the AC Amplifier clockwise a 1/4 turn and my compressor kicked on and cooled the vents to 48F. But at least it is fixed. Thank you for the assistance. Yes scope103 I did the checks on the harness side. (may have been misleading) Thanks again.
05-21-2017, 05:29 PM
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I'm "pretty" sure that adjustment on the top of the A/C amplifier represents an idle speed below which the compressor disengages. Alas, I can't find any reference to that in the manual. Also, that would be inconsistent with the AC idle-up VSV. I wish I could contribute more.
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05-21-2017, 05:56 PM
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I have never really understood that knob. I was always under the impression that it had something to do with how much the idle up valve increased RPM or controlled the point at which it opened and closed. It obviously does something. I have personally never fooled with mine. I don't currently use my AC due to a small leak or two but will be fixing it at some point in the future.
