Air Conditioning Coil Resistance

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The Professor
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My tercel:: 1987 Tercel SR5 4WD wagon
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Air Conditioning Coil Resistance

Post by The Professor »

Background: A/C does nothing when you hit the switch, nothing from the clutch. Following the troubleshooting tree in the FSM, I checked the fuse and it is fine. Next up is the clutch coil resistance...

The FSM says that you should see about 3.7 ohms at 68*F. It was about 60*F in my garage when I took the reading and got about 3.2/3.1 ohms. Is this too low? Where the heck would I start looking for a replacement coil?
1975 Subaru SuperStar wagon
1984 Subaru Turbo-Traction wagon & hardtop
1987 Subaru RX 3-door
1987 Subaru RX Type-RA 3-door
1987 Toyota Tercel SR5 wagon
1999 Subaru Forester S
2002 Subaru WRX sedan
2019 Subaru Outback 2.5i Limited
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rer233
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Re: Air Conditioning Coil Resistance

Post by rer233 »

Do you have 12 volts at the coil with engine running and A/C on?
if it aint there, there's a good chance it won't break!
83 SR5 Silver/Blue (Snowmobile/work beater)-totaled but drivable
85 SR5 Blue
88 SR5 White (the 'good' one)-not anymore-totaled
87 fwd silver wagon a/t
87 4wd dx Cream (a/t- not anymore- now m/t)
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Petros
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Re: Air Conditioning Coil Resistance

Post by Petros »

your coil is fine. I had this problem once, had the A/C serviced and it worked fine, several weeks later when I tried it again I got nothing, clutch would not engage. I jumped the clutch w/ 12v to test it and it worked fine, traced the circuit back to a relay on the unit under the glove box. all of the refrigerant leaked out and no pressure was in the system, the relay prevents you from running the system when it is empty.

So your system may be out of refrigerant, if so, that means there is likely a leak that needs to get fixed.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
The Professor
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My tercel:: 1987 Tercel SR5 4WD wagon
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Re: Air Conditioning Coil Resistance

Post by The Professor »

Is there a typical failure point in the A/C system? A soft or hard line that normally fails? My Tercel has lived a pretty gentle life with parts seeming to just have worn out, not having failed due to damage or misuse.
1975 Subaru SuperStar wagon
1984 Subaru Turbo-Traction wagon & hardtop
1987 Subaru RX 3-door
1987 Subaru RX Type-RA 3-door
1987 Toyota Tercel SR5 wagon
1999 Subaru Forester S
2002 Subaru WRX sedan
2019 Subaru Outback 2.5i Limited
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splatterdog
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Re: Air Conditioning Coil Resistance

Post by splatterdog »

If checking for power/ground at the clutch, jumper in a headlight bulb for a "load testing" test light. It only takes one strand of wire to satisfy a regular test light or meter.

There should be a low pressure switch that controls the relay Petros mentioned. It can be jumpered for a quick test, but do not jump it for more than it takes to see the clutch engage. No refrigerant=no oil flow..

Some cars also have a high pressure cut out switch, also for system protection.

Got a/c gauges?

The only thing typical with 30 year old cars is that it could be anything or everything!
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Petros
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Re: Air Conditioning Coil Resistance

Post by Petros »

seals dry up and leak, which is usually what goes first and most common. but as splaterdog points out, on a system this old it can be anything that could fail. I am told by our local a/c shop that the systems in toyotas are reliable and very durable. so take your chances.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
The Professor
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My tercel:: 1987 Tercel SR5 4WD wagon
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Re: Air Conditioning Coil Resistance

Post by The Professor »

Got the dash apart last night and the A/C switch and thermistor both ohm out no problems, but I didn't do the ice water test on the thermistor because I couldn't figure out how to remove it. Next up is the A/C amplifier...
1975 Subaru SuperStar wagon
1984 Subaru Turbo-Traction wagon & hardtop
1987 Subaru RX 3-door
1987 Subaru RX Type-RA 3-door
1987 Toyota Tercel SR5 wagon
1999 Subaru Forester S
2002 Subaru WRX sedan
2019 Subaru Outback 2.5i Limited
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rer233
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Re: Air Conditioning Coil Resistance

Post by rer233 »

Are you sure the system is fully charged?
if it aint there, there's a good chance it won't break!
83 SR5 Silver/Blue (Snowmobile/work beater)-totaled but drivable
85 SR5 Blue
88 SR5 White (the 'good' one)-not anymore-totaled
87 fwd silver wagon a/t
87 4wd dx Cream (a/t- not anymore- now m/t)
The Professor
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Posts: 650
Joined: Wed May 12, 2010 6:38 pm
My tercel:: 1987 Tercel SR5 4WD wagon
Location: Western Washington
Contact:

Re: Air Conditioning Coil Resistance

Post by The Professor »

rer233 wrote: Fri Oct 20, 2017 9:18 am Are you sure the system is fully charged?
No I'm not, but I'd rather run through the A/C troubleshooting tree in order before I take the car to a shop with gauges. Could be as simple as a failed pressure switch. If the first branch of the TS tree comes up without a solution, the next step is to check system pressure with gauges, if I remember correctly. This also gives me an opportunity to troubleshoot the failed radio, failed HVAC illumination, etc.
1975 Subaru SuperStar wagon
1984 Subaru Turbo-Traction wagon & hardtop
1987 Subaru RX 3-door
1987 Subaru RX Type-RA 3-door
1987 Toyota Tercel SR5 wagon
1999 Subaru Forester S
2002 Subaru WRX sedan
2019 Subaru Outback 2.5i Limited
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splatterdog
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Re: Air Conditioning Coil Resistance

Post by splatterdog »

The low pressure switch usually goes open circuit when below pressure limit.
TracDoc
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My tercel:: 1985 Deluxe

Re: Air Conditioning Coil Resistance

Post by TracDoc »

I had the same problem on my 85. The problem was a broken wire that connects to the distributor igniter. The wire on my 85 is blue. The wire supplies power to the A/C amplifier. The amplifier supplies power to the A/C clutch. Look in the back of the service manual at the wiring diagrams and you should be able to see the color and location of the wire. Before I located the break, I connected a hot jumper wire to the wiring harness connector where the blue wire is connected. Doing this activated the clutch, so, I knew I had found the problem. If you use the jumper wire, be sure to put a fuse in the line (10 amp for the 85).
The Professor
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My tercel:: 1987 Tercel SR5 4WD wagon
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Re: Air Conditioning Coil Resistance

Post by The Professor »

TracDoc, Thanks for the advice! I'll give that a try!
1975 Subaru SuperStar wagon
1984 Subaru Turbo-Traction wagon & hardtop
1987 Subaru RX 3-door
1987 Subaru RX Type-RA 3-door
1987 Toyota Tercel SR5 wagon
1999 Subaru Forester S
2002 Subaru WRX sedan
2019 Subaru Outback 2.5i Limited
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