I have a 1995 Volvo 850T wagon with A/C issues. This car has ECC. I know that the evaporator leaks slowly, but will hold enough r134a through the summer.

The symptom: The A/C clutch turns off, which then causes the car to blow hot air. This usually happens after the A/C has been on a while (10+ minutes), and the external temperature reading (on the dash display) exceeds 95 degrees. THe A/C will then turn back on in a few minutes. Then turn off again and get hot, etc.

Also, this is definitely linked to external temperature. When the external temp is below 90 degrees, the A/C works beautifully.

What I have checked:
1) Checked refrigerant level. Currenty reads just over 30 psi when the compressor runs (holds steady, fully charged a month ago)
2) Jumpered Pressure switch to verify it was not that. Pressure switch is operational.
3) Compressor runs with pressure switch connector jumpered. Checked voltage to clutch @ compressor. Voltage stops, then clutch stops. Something is telling the A/C to stop voltage to the clutch. Compressor is noisy.
4) No trouble lights blinking, no blinking recirc light, no blinking AC light on ECC unit.
5) Pulled codes. No codes. Unfortunately my code reader will not read A/C info.
6) When the A/C compressor cycles, it cycles on for about 10 minutes, then off, for more than 5 minuites, then on again for 10 minutes. When running on the highway, the A/C never shuts off.

What should I check next?

 

Are you 100% sure you loose power at the compressor?
Did you bypass the sensor in the compressor already?

 

There looks to be one wire coming from the wiring harness to a connector, to what looks like a resistor block to the Clutch. Checking the voltage at the point where the wire connects from the harness to the wire on the compressor indicates that voltage drops from 12 to 0 when the compressor shuts off.

 

Maybe the switch is already bypassed. There should be a sensor on the back of the compressor by the lines.

Could either be a bad High pressure switch,Low pressure switch, or a bad cooling fan.

 

What I thought was the wire leading from the harness was the wire leading from the sensor in the back of the compressor to the clutch. Re-checked the wire from the harness, and reads 12 volts before the sensor in the back of the compresssor, 0 volts @ the connection to the clutch wire. So, it looks like I am ordering a new compressor, and will also order a new receiver/dryer (accumulator) as well. Thanks for the detail on where the sensor is located.

A related question: How does the ECC unit know to adjust the air flow? Does it have cabin sensors, etc.? I used to own a Saab with a similar system, and it had a cabin sensor, dash sensor, blower motor sensor, external temp sensor, and one other I cannot remember. The cabin air sensor would get gummed up with dust and need an occasional cleaning. Is the Volvo similar?

 

Did you try bypassing the switch it can be done then the compressor might work.

Yes there is a cabin temp sensor it is located by the drivers side grab handle in the roof.

 

what would be the negative impact of bypassing the switch on the compressor? Bypassing that switch would be a whole lot less expensive than replacing the compressor.

 

None really except maybe wearing it out a little sooner.

But I have seen cars have the switch bypassed for years with no problems.

 

Have a 2007 S40 2.4i
Thought I needed to recharge my ac as it blew warm to cool air. Hooked up recharge container and system was good.
Was going to change the cabin air filter anyway. The amount of crap that came out was stunning.
Changed filter and the ac about blew my face off. It blew twice as hard and was cold.
All the debris caught in the filter prevented the air from moving thru.
Three pics below.

Debris from cabin filter

Filter tore as pulled out but you can see how, clogged it was.

Leaves, pine needles and who knows what else's that was trapped by cabin air filter.