So I may have made some bad assumptions. There is a relay for the ac compressor under the hood in my '98 V70. It has a hot line in (term 3) and two terminals (numbers 1 and 2) between a coil that read 13+V. The relay suggest that when I turn the AC on at the climate control on the dash - that either the number 1 or 2 terminal would ground out creating a voltage drop through the coil which would induce a magnetic field capable of "closing" a switch which connects terminal 3 to terminal 5. Terminal 5 goes to the compressor.

My thought was that my climate control was bad - since I did not get a voltage drop when I activated the AC on button. THIS IS WHERE I THINK I MADE A BAD ASSUMPTION. I decided to bypass this stuff (since the climate control units are very expensive) so I put a switch in that would connect Terminal 3 to Terminal 5 - thus powering up the compressor.

As a side - I first thought that my coolant was low - when I took it in the shop said I had plenty of charge and that the problem was somewhere else.

Well once I added the switch I had a nice cold AC for a week. But today my wife thought the car was overheating (the AC bypass switch was on) when a bunch of white "smoke" started pouring out from under the hood. Since I've determined that the car did not overheat I think that I activated some high pressure release valve and dumped some of the coolant.

So - question is - is the AC relay that I bypassed controlled by several systems? Meaning does the AC on button on the climate control talk to a pressure (high or low) sensor - or any other sensors prior to activating the AC relay? If so, then my climate control could be good - and the problem could be with a sensor, or with the charge still?

Also, does anyone know if I caused any permanent damage by bypassing the ac relay? I'm stumped and concerned that my actions may have caused me much bigger problems. Any help or insight or suggestions are welcomed.

Hey, just wondering here, you checked the climate control OBD?

prolly won't give you much, but maybe you'll get lucky...

http://farm5.static.flickr.com/4093/4796907493_5787e9edae_b.jpg

I wouldn't mess with the AC relay, except to replace it if needed. It is possible that the pressostat has failed, easy to check or replace. Same with the clutch gap at the compressor.

When I over charged my system, the mechanical release valve blew with a big bang and I would up with a lot of PAG oil under the engine. I had charged the system at 65F and it blew out at over 85F. R134a tends to expand a lot with heat :) The AC continued to work after the blowout.

It is possible that the AC switch on the climate control needs to be cleaned up. This is possible after you take the unit out and remove the face. Just do not hurry the project.

So, check the pressostat switch on the low pressure line. Check the clutch gap, it should not exceed .040 inch.

Klaus
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Why are Volvos so endearing? Its just a car.

Is the pressostat switch also known as the "low Pressure" switch? The low pressure switch on the line near the firewall on the passenger side seems to be working right. Meaning it's a closed circuit now.

There is another switch near the low pressure valve (near passenger side headlight). This switch has a 5volt power in and two lines out. I think that one line goes to the fan and the other goes to the compressor. The fan is switching on so I think that this one is functioning too.

I don't think that it is a gap issue - as when I bypass all of the sensors and provide voltage from the battery directly to the compressor everything works.

Do you know if there is a way to bench test the climate control unit (these seem to be pretty pricey)?

Also, do you know if there is any other switch or sensor between the climate control unit and the relay. I am positive that whatever "unit/control/sensor/etc" that provides a ground for the low side relay coil to "close" the switch to the compressor is not doing its job. I thought that this would be the climate control unit, but I can't find continuity between either of the low side relay terminals and ANY of the terminals that plug into the back of the climate control unit.

If you unplug the pressostat switch and jump the 2 leads, with the engine running, the clutch should activate.

The clutch needs 13V to engage. If you give it 14V directly from the battery, it will also engage and allow for a larger clutch gap.

There is an inline thermostat on the wires going to the compressor, which cut power when too hot. Because of the 'white smoke', check those wires running around the bottom of the compressor.

If you have access to a pick&pull, get a pressostat and a relay. Same items in the 850s. An 850 ECC unit will not work in your car.

Klaus
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Why are Volvos so endearing? Its just a car.

when I bypassed the relay I didnot jump to the battery, I used jumped terminal 3 to 5 at te relay. This is a 13.06V supply. I took off the connector at the pressostat and shorted the two terminals and still no compressor. Is there another sensor that has to give the ok. I also took to my local volvo dismantlers (very reliable and knowledgable) they let me put in another working climate control but no luck. There is also a switch (or maybe sensor) right next to the window washhing fill tube, this is hooked up to both the fan and the ac system (has a three prong connector and is bolted to the ac line with a 14mm threaded fitting) they suggested this may have failed so they changed it out with a working one but again no compressor.

any othe ideas. Could it be the OBD?

I lifted the following from the 850 manual, most of it still applies to 1998. The 850 AC relay was only 4 pin. The relay does talk to the ECU and the ECC.

Your testing another ECC and high pressure switch unit was good, too bad you couldn't find a relay. The 'white' smoke still bothers me, that usually indicates a burning wire. Did you check the wires that run around the bottom of the compressor? I hope you didn't fry the internals of the clutch while bypassing the relay.

Klaus

The Electronic Climate Control (ECC) module (A/C-heater
control panel) contains a function selector dial, driver’s and
passenger’s temperature dials, a REC (recirculated air) switch, A/C
OFF switch, and a fan speed (blower motor) control lever. See Fig. 1.
The heater (blower motor) fan is controlled by ECC output (power)
stage. Air conditioning system will only operate above 32F. Blower switch must not be in zero position to allow compressor to engage.

Other system components include an A/C relay, A/C compressor,
low-pressure switch (pressostat), A/C safety and high-pressure switch,
engine coolant temperature sensor, outside temperature sensor,
interior temperature sensors, and duct temperature sensors.
In addition, driver’s and passenger’s temperature control
damper motors, recirculation damper motor, floor/defroster damper
motor, ventilation damper motor, and diagnostic connectors (units)
complete system.

A/C relay. Compressor operation requires that the A/C relay be
activated by both Electronic Climate Control (ECC) module and Engine
Control Module (ECM). The ECM turns A/C compressor off when engine is
at full acceleration, at high engine temperature, and for 5-10 seconds
after starting engine.

The ECC control module normally supplies voltage to A/C
relay, except when heater (blower motor) fan is off and vehicle speed
is less than 20 MPH, when heater fan is off and recirculation is on,
or momentarily when under full acceleration.

If A/C is switched off using the AC OFF switch, ECC control
module will cut supply voltage to relay, turning off compressor.
However, this does not apply when air distribution control is in
defrost setting, since A/C is always on in this case.

The A/C compressor is connected in series with the lowpressure
switch, high-pressure switch, and safety switch. The highpressure
and safety switch cut power to the A/C compressor if pressure
in the A/C high-pressure circuit becomes excessive, supplying a signal
to ECM to start cooling fan.

The low-pressure switch (pressostat) turns A/C compressor on
and off to maintain pressure within limits.
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Why are Volvos so endearing? Its just a car.

There is a switch on the line right after the fill port on the low side, if that switch doesn't tell the ac to turn on, it won't. Check there for voltage when you switch it on. Good luck.


You don't hear the clutch click, right? Sometimes the clutch gap is too high and the clutch won't engage the compressor.

I did a bit more probing and found that the number 1 and 2 terminals at the relay DO NOT have continuity with any of the leads out of the climate control. This must mean that the climate control first "talks" to some other sensor/switch prior to sending the relay signal.

I will look at the low side switch you refer to. The only way that I get the AC to go on is to "jump" the relay. When I jumped the relay the AC did come on. Not anymore though - since the high pressure release was activated.

The a/c compressor is switched on by the relay via a signal from both the climate control unit and the ECU. If you jumper the relay and the compressor will not come on, it could be the windings in the clutch magnet have burned out...hence the white smoke. I don't know off hand what the resistance of the clutch coil should be but probably next to nothing. Check with an ohm meter. good luck