AC not blowing cold unless moving
Thread Starter
Heel & Toe
Joined: May 2017
Posts: 19
Likes: 1
From: Minnesota
AC not blowing cold unless moving
The problem started the other day. It is not blowing nearly as cold as it was. I tried to refill the refrigerant but the guage read the pressure in the red, so I tried to relieve pressure but it wouldn’t budge. The compressor seems to be working fine. I noticed the fans weren’t coming on with the AC, but they were still coming on at operating temps. Please help
Tech Contributor
Joined: Oct 1999
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From: Charlotte, NC (formerly Endicott, NY)
If the fans are not on when the vehicle is idling with a low coolant temp (below 200) and a low oil temp (below 200) with the AC turned on it is possible the AC request signal isn't getting through to the PCM. The PCM sends the signals to the fan relay circuit telling it whether it should be on, low speed or high speed. The AC controller in the dash sends grounds the AC request signal that is one of the inputs to the PCM. If that ground isn't being applied then you would have the problem you are describing. However, refrigerant levels can alter what is happening since too much pressure can turn the AC compressor off.
I would say check the fan relays first but C5s are old cars and the wiring can get screwed up due to damage caused by POs and connections will tend to deteriorate with age due to dirt and corrosion so unlike a new car relays aren't necessarily the top concern on a list.
Bill
I would say check the fan relays first but C5s are old cars and the wiring can get screwed up due to damage caused by POs and connections will tend to deteriorate with age due to dirt and corrosion so unlike a new car relays aren't necessarily the top concern on a list.
Bill
Last edited by Bill Dearborn; Jul 5, 2018 at 09:47 PM.
Tech Contributor
Joined: Oct 1999
Posts: 41,036
Likes: 9,798
From: Charlotte, NC (formerly Endicott, NY)
Bill
Thread Starter
Heel & Toe
Joined: May 2017
Posts: 19
Likes: 1
From: Minnesota
That was my first thought as well. Poor cooling at low speeds and better at high speeds is a sure indicator of low refrigerant level. However, based on the actions he described he may have overfilled the system and he says the fans don't come on as soon as the AC is selected. I assume he knows whether the fans are coming on or not. If the fans don't come on until the car gets up to operating temp instead of as soon as the AC is turned on that is an indication there is an issue with the signal going from the HVAC controller to the PCM. The PCM has control of the fan relays and if it doesn't know the AC is turned on it won't turn on the fans. It shouldn't make a difference whether the system is over or under charged as far as fan operation. Lack of fan operation at low speed low operating temps would also fit his scenario. If the fans are operating the way they do for engine cooling due to not knowing the AC is turned on his AC cooling could vary up and down while driving at slow speeds.
Bill
Bill
