AC doesn't work while stopped

Tiny
JOSHSCIVIC
  • MEMBER
  • 1999 HONDA CIVIC
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 150,236 MILES
The AC on my 1999 Honda Civic 1.6 SOHC was not working well. I recharged the system it mostly works. It doesn't work well when I am at idle at a stop light or parked. I have the impression that the engine compartment needs to be cool enough for the AC to work properly. I thought the radiator fan wasn't coming on frequently enough so I ran a temporary toggle switch to keep the radiator fan on and it allows the AC to keep blowing cold air while stopped. However, in trouble shooting the radiator fan, I believe it is working correctly. I used a IR thermometer to check the temperature of the thermostat housing and the radiator fan kicks on when it reads 193 degrees (book says it should come on at 196). It only stays on for a minute but as soon as it goes off, the thermostat housing temperature is 180 degrees. Seems ok to me. I put a gauge set on and here is what I found:
Engine off- Low side spikes high and High side reads 100
Engine cold with AC off- Low side spikes high and High side reads 100 (no change from engine being off)
Turn AC on before engine gets up to temperature and the guages read 20 on the Low side and 140 on the high side
Once the engine gets up to temperature the Low side reads about 50 and the High side stays at 140.
As soon as I shut off the AC, the Low side goes up to 60 and slowly but steadily rises and the High side drops to 100 but eventually comes back to 140.
The book I have says that normal operating pressures are Low Side 23-36 and High side 240 to 300.
I have to admit that I'm a bit confused by the book I have as there may be more than one cause to my problem ranging from a "slightly low charge" to an Expansion Valve problem. Per the book, with a high reading on the Low Side and a low reading on the High Side, I should have a "noisy compressor" but the compressor is working fine. Any insight? PS- I haven't dug into the evaporator area but I don't see any leaks (I used a dye when I recharged last month). I have considered an after market fan control switch which will turn on the radiator fan whenever the AC is turned on but I'm not sure what the consequences are of running the coolant to cold. (If that is even a concern). I hope I have given enough information for you to help.
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Friday, August 12th, 2011 AT 1:52 AM

11 Replies

Tiny
JOSHSCIVIC
  • MEMBER
Also, yes- the condenser fan comes on when the AC is turned on- replaced that motor a couple of weeks ago.
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Friday, August 12th, 2011 AT 2:08 AM
Tiny
JOSHSCIVIC
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Thinking of more information (sorry)- when I changed out the condenser fan motor a couple of weeks ago I cleaned the fins with a brush, AC coil cleaner, water and compressed air.
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Friday, August 12th, 2011 AT 2:12 AM
Tiny
KHLOW2008
  • EXPERT
The readings indicates that freon level is possibly low with a low side reading of 20 and 140.

A 50/140 reading indicates the compressor is weak with low freon level.

Yours is an automatic transmission therefor both cooling fans should come on when A/C is turned on. If any is not working, you need to check the relays.
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Friday, August 12th, 2011 AT 1:04 PM
Tiny
JOSHSCIVIC
  • MEMBER
Thankyou. I put some dye in last month and I think I found a leak coming off the compressor by the rotor or pressure plate. The dye was red and I think I see a streak on the splash guard- red dye on black plastic is not easy to see so I'm going to get some UV dye and see if I can confirm. However, I still have the fan problem. All the relays work as they should. I'm thinking I have a problem with the ECM. What do you think?
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Tuesday, August 16th, 2011 AT 11:05 PM
Tiny
KHLOW2008
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Nope, should bot be the ECM.

Have you tested the fan motors?
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Tuesday, August 16th, 2011 AT 11:25 PM
Tiny
JOSHSCIVIC
  • MEMBER
Yes. Both fan motors work- Condenser works when AC comes on and radiator fan comes on when the circut is closed on the ECT. (Both work with a hot jump too) I also jumped the power circuits in the relay slot and the radiator fan came on. When I jumped the power circuit on the condenser fan, I just heard a click coming from somewhere around the compressor. Not sure if the other electronics, such as AC clutch relay have anything to do with it but when I put the condenser fan relay back in and turned on the AC, the fan came on as expected. Just can't get them to come on at the same time (when turning on AC) unless the coolant temp gets high enough to trigger the radiator fan.
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Wednesday, August 17th, 2011 AT 2:08 AM
Tiny
KHLOW2008
  • EXPERT
Here are the schematic for the cooling fan system. From the first two diagram, seems the fans works individually and the radiator cooling fan does not work with the A/C compressor.

However the A/C system indicates the PCM is responsible for the radiator cooling fan to come on when the A/C is turned on. Seems the PCM ground circuit for the radiator fan relay is not worling correctly.

Try using a test lamp to ground the A20 terminal of the PCNM to see if the radiator fan comes on with the ECT switch disconnected.
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Wednesday, August 17th, 2011 AT 1:05 PM
Tiny
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  • MEMBER
Alright, pulled the ECT, pulled connector A and grounded the port for A20 on the wiring harness/connector. The radiator fan came on! I checked for a ground on the PCM/ECM A20 terminal and got nothing. I ran a jumper from PCM terminal A20 to the port on the connector and got nothing. I'm not sure how the PCM/ECM is grounded. I connected a temporary ground to the slot where the bolt holds the unit to the car and reconnected Connector A and got nothing. My assumption is that no ground is being sent to terminal A20 on the PCM.
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Saturday, August 20th, 2011 AT 4:28 PM
Tiny
KHLOW2008
  • EXPERT
The PCM grounds the circuit when signals from the AC is recieved. This circuit is not working and the likely cause is the PCM itself.

Guess you would have to try substituting the PCM.
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Sunday, August 21st, 2011 AT 5:02 AM
Tiny
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  • MEMBER
I thought the conversation was going there. Thanks for your help.
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Wednesday, August 24th, 2011 AT 1:49 AM
Tiny
KHLOW2008
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Was problem resolved?
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Sunday, October 21st, 2012 AT 5:01 AM

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