Hello. I have a 1998 Volvo S70 sedan (stick shift) and the air conditioning is blowing out warm air. It used to get very cold. Do I need to replace my air compressor valve and dryer? Or what?

I would look at all the fuse .You only need one thats got a fine airline crack .And all eath points in the engine bay .

Are you getting coolant flow through the heater core? These cars have common problems with heater cores but they are easy to replace. IPD has a Video on U-Tube with step by step instructions. Also if you are in very cold weather have you checked your anti-freeze? I saw a Toyota last year freeze completely because of no anti-freeze. It took days to thaw out the heater core and they were lucky that the ice did not blow it apart. It took me hours of starting it and running up to a low temp and shutting it down to get it drivable.

before I do a job like this i always buy a haynes repair manual for my year and car. take the time to read up on this and then well knowledged i go for it.
Good luck and thanks for your question and I hope my suggestions help. Don't forget to rate me.
burdfrenzy
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STARTER & ALTERNATOR REPLACEMENT PROCEDURES FOR 1998 Volvo S70 AUTOMOBILES
Includes starter and alternator replacement procedures for domestic and imported 1998 Volvo S70 cars and light trucks from 1990+.

Alternator, Replace -> With Air Conditioning -> Without Air Conditioning
Vehicle: 1998 Volvo S70 2.3 L5 GAS

With Air Conditioning

• Disconnect battery ground cable at battery.
• Detach pipe from control module box.
• Remove auxiliaries belt.
• Remove power steering pump and place it on top of engine.
• Remove upper bolt.
• Remove bolts common to alternator and compressor; lower bolts on alternator and upper bolts on compressor.
• Raise and support vehicle.
• Loosen lower bolts for compressor (so that there is some clearance).
• Remove air baffle.
• Lower vehicle.
• Disconnect warning lamp positive lead and connector from alternator.
• Pull alternator upwards/away.
• Remove alternator from vehicle.
• Reverse proc...

Hello sounds like the thermostat is stuck open. This device opens and shuts depending on the temperature of the engine. When the engine gets to a certain temperature it will open allowing hot water to circulate to the heater matrix which warms up the car interior. As yours is possibly stuck open the cold water is just being circulated, hence blowing cool air. You should notice the temperature gauge stays very low unless you are stuck in traffic where it will rise. This is a cheap fix so no need to worry.

You have air in the cooling system.

Please see my tip at http://www.fixya.com/cars/r6235876-no_heat_fan_blowing_cold_air . These are generic instructions. If you get stuck or need specific instructions for your car, please get back to me with model, year and engine info.

Go to the dealer and get the code. To reset the radio. You have to leave it for like 12 hours with the ignition on. At the dealer we used to hook the car to a charger and leave it with the ignition on over night.

Sounds like the AC system is overcharged. You will have to go somewhere and have the system evacuated and recharged to get the right level.

Your Heater Core is Bad= Coolant on Pass Floor
If A/C Does NOT blow Cold anymore the Evaperator Core is Leaking
First time I have seen them BOTH go Bad in 30 rs of Bein A Mech/Tech

I AM AN ASE CERTIFIED VOLVO----MASTER TECH AND YOUR PROBLEM W`HICH IS COMMON ON ALL 850,S ANDS70,S THE PROBLEM IS PROBALLY AT LEAST 70% DUE TO AN AIR-FLOW RISTRICTION TO THE CONDENSOR FIRST IS SYSTEM AT FULL CHARGE LOW SIDE 25-33 PSI AND YOU AND I REPEAT ONLY CHARGE SYSTEM ON THE LOW SIDE THERE IS NO AND I REPEAT NO HIGH PRESSURE CONNECTOR AND WHAT I WOULD DO IS RUN AGOOD THICK WIRE FROM A/C COMPRESSOR AND A 30 AMP FUSE FROM A CIRCUIT LIKE THE HEATED SEATS FROM INSIDE THE CAR WITH A TOGGLE SWITCH AND A THERMOMETER IN CENTER AIR DUCT AND MANUALLY SHUT THE SYSTEM DOWN IF IT FALLS BELOW 40 DEGREES AND WATCH THE THERMOMETER EVERY 7 MINUTES AND THE MAIN PROBLEM IS THE ENGINE FAN CIRCUIT I HAVE DONE DOZENS OF THESE AND THE PROCEDURE IS WHAT I WROTE

Hello Joan,
The climate controls on your Volvo are all electronic at the control end, but likely have little vacuum motors to control the opening and closing of heater valves and air directional flaps in the innards of the dashboard. With the "mature" nature of your vehicle, it is sometimes a cracked vacuum hose or that the rubber end is getting a little hard and now leaking at the nipple where it is plugging into the vacuum valve. IF this is the issue, you MAY be able to here a hissing noise immediately after turning off the engine. Crawl down and get your head (ears) right under the dash. There may be a cardboard/plastic cover plate on the underside of the dash that you have to remove to get access.
But from the symptoms that you describe in your post, "Temperature dial has lost it's clicks"... I SUSPECT that the contacts on the control module may be totally worn out for both the direction of flow and the temperature control. Modules are available on eBay/Amazon (usually used) and it should be quite straight forward on how to remove / replace. The link below provides both links to purchase the control and also some YouTubes on how to replace it.
Hey... do you have a Pick-n-Pull or similar self-serve auto-wrecker near by? Often you can see what vehicles they have on their lot. It appears that s70 v70 and c 70 Volvos from 1998-2000 all have the same control unit. I've also included the part number in one of the photos... do a search for that and you may find more hits.

I hope this helps you Joan!
1998 Volvo S70 2 0 Google Search