A/C worked fine all summer, heater pilot light lit yesterday, now a/c blows hot air?

We're renting a house, moved here in Feb, used the heat till around April. Then switched to a/c when it started getting hot outside. Heat a/c worked fine all summer. Husband replaced the thermostat at the end of June because the arm/lever thingy you use to adjust the temperature was broken off before we moved in. So we've used the a/c all summer, no problems at all. Over the weekend it got cool, so I turned the heat on Saturday morning and after 2 hours of blowing cool air I realized the pilot light on the furnace needed to be lit. So when the handyman who has been painting the outside of the house for a couple of weeks came I asked him if he could light it. He said he'll call the landlord (his boss) to do it. It gets lit, heater works fine. Later yesterday afternoon it got hot outside so I turned on the a/c only to find that it blows warm/hot air, even all the way down to 45 degree. We've tried this 3 or 4 times since yest. afternoon and it still blows warm air. What is wrong?

A/C worked fine all summer, heater pilot light lit yesterday, now a/c blows hot air?
it's likely the A - Frame is a block of Ice. Called the landlord and have them call the HVAC person.
Reply:Just open your windows. I havent' used AC since July and it's been pretty cool in the house
Reply:check and see if both the ac and heat are on at the same time .i suspect the connections to the thermostat are wrong .if it is a 4 wire system .then red is your 24 volts .green is your fan .white is your heat and yellow is your ac [.if there is a r-c and a r-h lug on the thermostat .jump white to r-h and jump yellow to r-c .but only if you still have a problem after you install the 4 wires ]
Reply:if you look at thermostats at the store you will see that there are three and four wire types. If you saved the old one check it out and maybe take it to the store and ask what the replacement is. If you have the correct one, you may have wired it wrong. Easy to do. Terminals should have a color code or check the installation instructions. If yiou tossed them go back to the store and look at the ones in the package.
Reply:check the wires on the thermostat they could be touching in the wall or the thermostat is wired wrong and you did not know it because of the pilot lite was out